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Metals in Distilling

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  • Harry
    As promised, the first draft of the metals paper. It is incomplete, and remains a work in progress , subject to alteration without notice. However there
    Message 1 of 5 , May 27, 2006
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      As promised, the first draft of the metals paper.  It is incomplete, and remains a 'work in progress', subject to alteration without notice.  However there should be enough info in it to give some food for thought, which is what the 'spirit' of this group is about (hopefully).It is a long dissertation, so feel free to read, save or discard as you see fit.Slainte! regards Harry

       

      Chapter 03 - Metals

       

      From time to time, the subject comes up of `what metals can or can't be used in distilling equipment'.  A very simple and safe rule of thumb is this: for contact with alcohol or its feedstock, never use any metal that is not used in commercial distilleries for that stage of processing.  While this may be the easiest approach, it tells you very little about why this or that metal is acceptable or not.  Any distiller worth his salt should know exactly why a particular material or procedure is employed.  Therefore a more complete analysis is in order.

       

      As a starting point, let's take a look at the metals in commercial distilling plants.  Black iron, cast iron, galvanized iron, steel, stainless steel, copper, chromium, aluminium, lead, zinc, nickel, brass, various alloys, and several other metals in smaller proportions are all found somewhere in a distillery.  That does not mean they should all be used in the distillation process.  On the contrary, most of the aforementioned metals are found in the construction of buildings, peripheral and non-critical machinery.  For the distilling process proper, where alcohol and vapours are being manipulated, there are only four acceptable metals to use, namely silver, copper, treated brass, and stainless steel.  The reasons why will become clear as you read further.

       

      Beverage alcohol and the feedstock it is derived from are classed as foods meant for human consumption.  Grains, fruits, sugars, ethanol liquid and vapours, and yeasts; all are categorized as foodstuffs.  There are very strict rules and regulations governing what materials are allowed to come in contact with foods during processing, storage and packaging.  These regulations have been formulated after many years of rigorous testing of materials and their influence on the foods in question and/or the affects they have on human metabolism.  Many countries adopt the policies of International monitoring bodies such as the World Health Organization (WHO).  This body has published information and recommendations for the materials likely to come into contact with foods.

       

      Like many substances in common usage, the pH of foodstuffs plays an important role in determining which metals are suitable for food contact.  Whether a food is acidic, such as tomatoes and soft fruits, or neutral or (less common) basic, has a marked influence on the types of metals and other materials such as plastics that can be allowed for processing and storage.  The temperature of the foodstuff also plays a part in determining suitability or otherwise as many foods when hot have accelerated reactions in contact with metals.  It should be noted here that commercial processing and domestic or household usage of materials for food contact are two separate situations.  In a commercial distillery, everything is subject to regulations regarding suitability, safety, and consumer protection and well-being.  There are no such safeguards for household usage, save for commonsense and `current practice' methodology.  However, as I intimated earlier, a hobby distiller should at least try to follow the practices of commercial processing.  Therein lies safety and relative peace of mind.

       

      The reaction of a metal in contact with foodstuffs is a selection criteria used predominately to avoid metal corrosion and mechanical failure, necessitating costly replacement of equipment.  Mashes or `worts' will almost always be acidic, as it is a requirement of yeast to have an acidic environment to perform its functions of producing ethanol and other desirable substances.  Mashes fermented by yeasts tend to become more acidic as the fermentation progresses.  Thus the completed wash or `beer' will have a pH of nominally 4.0 or even lower.  When fermentation is finished, this acidic beer is now charged to the still and heated.  Elementary school chemistry teaches that hot acids are extremely corrosive to certain metals, notably aluminium, black iron, certain steels and tin.  For this reason alone, the aforementioned metals are not really suitable for stillpots, boilers or re-boilers, unless of course you like the idea of frequently replacing components of your still.  You will note this corrosion resistivity is a separate issue and has nothing to do with possible metal migration into the foodstuff or chemical reactions that may form undesirable substances in the wash.  That is a selection criterion we'll look at later.

       

      Regardless of regulations, commonsense tells you that all still parts likely to come into contact with hot acidic liquids and vapours should be made from a material relatively impervious to corrosion, heat, and toxic leaching of chemicals.  Copper, food-grade or Austenitic stainless steel (304 & 316), and correctly treated brass fill this role admirably.  I will deal with each in turn, but while we're on the subject of `treated' metals I should make mention of two other metals sometimes considered by the unwary, namely Tin or Tinplate, and Galvanized Iron.

       

       Easily corroded metals such as Black Iron are often coated with a surface layer of chemicals or other metals to protect the base metal from corrosion.  What is not understood by many people is that the composite material is meant to be used in normal everyday use, not in harsh chemical processing environments.  The galvanizing on the surface of the Iron contains Zinc, which is a toxic metal that leaches badly under hot acidic conditions.  The Zinc is rapidly eaten away and finishes up in the distillate.  The base Iron is then exposed to the acidic wash, resulting in corrosion (rust), which also gets into the processing chain.  The stillpot wears out very quickly and needs to be replaced frequently.  Galvanized Iron has no place in process distilling of  foodstuffs such as beverage alcohol.

       

      Similarly, Tin is attacked by both acids and bases (alkali) but has the curious property of being relatively stable under neutral pH conditions.  For this reason, it was commonly used in centuries past as an alternative to copper.  However to use Tin, the stillman had to be sure the wash was brought to a neutral pH condition, not always an easy thing to do given the crude and inaccurate measuring instruments and methods (or lack thereof) employed in bygone eras.  It is a source of much confusion when the distillers of old tell the young folk "You gotta neutralise the beer".  So `young pistol' follows this sage advice and adds Sodium Bicarbonate (a neutralising buffer, pH 8.5) to the beer in his brand new copper potstill (tinplate has been largely superseded).  Then he gets the fright of his life when the distillate runs with a pretty bright blue colour.  The blue is, of course, the well-known Cuprous Hydroxide or Schweitzer's Reagent, formed by a complex chemical reaction triggered by the neutral-to-alkaline conditions set up in the Copper still by the S. Bicarbonate.  If Tin were the construction material used, there would be no such reaction.

       

      One must always use caution when evaluating procedures from the past.  Manufacturers from every era strive to refine their processes based on the materials and knowledge at hand.  However time marches on, and advances in Science & Technology march right along with it.

       

       

      Corrosion of Metals

       

      The biggest problem with most metals in distilling, or indeed most processing-type applications, is corrosion.  Often it is the deciding factor when weighing up the suitability of a metal for a particular duty.  It is the driving force behind mankind's quest for newer and more durable metal alloys.

       

       

      Corrosion occurs when the exposed metal surface reacts electrochemically with the surrounding medium in the presence of moisture and oxygen.  This reaction results in the formation of surface compounds of the metal (e.g. hydroxides).  The rate at which corrosion proceeds will depend in part on the composition of the aqueous medium.  Corrosion of iron in very pure water will be considerably slower than in water containing acids or salts.

       

      The rate of corrosion depends also on the solubility of the formed compounds in the medium, and their rate of removal.  Thus the formed compounds may be removed rapidly in a flowing aqueous medium, and the corrosion rate will be high (thinning of the walls of water pipes).  In a static medium, the rate of corrosion will be moderated as the ionic concentration of the surrounding medium increases.

       

      Corrosion products formed in the atmosphere are more or less adherent e.g. rust on iron, verdigris on copper.  Rust is essentially hydrated ferric oxide which usually also contains some ferrous oxide and may contain iron carbonates and/or sulfates.  The equivalent in copper is verdigris, consisting mainly of basic copper carbonate, but may also contain copper sulfates and chlorides. However, rust forms loose scale and is easily removed, while verdigris forms a stable patina on the Copper surface.

       

       

      Corrosion resistance

       

      Some metals (e.g. aluminium, chromium) are rendered "passive" (very resistant to corrosion) by the spontaneous formation, in the presence of oxygen, of an invisible and impermeable oxide film a few Angstrom units (0.1 nanometers) thick. This passive layer is very strong, very adherent and self-repairing if it is damaged.  One of the main reasons for the production and use of metallic alloys is that alloys are virtually always more resistant to corrosion than are their basic metal components.

       

      This is partly due to the fact that migration of the constituent elements is much lower than migration from non-alloyed metals, because of the micro-structural binding of the elements within the alloys.  Stainless steels, which are alloys of iron with a minimum of 10.5% chromium, are orders of magnitude more resistant to corrosion than iron itself.  This is partly because they possess the general properties of alloys, referred to above, but mainly because they have a surface "passive film" which is naturally and rapidly formed on contact with the oxygen in air or water.  Stainless steels used in food contact applications are invariably used in the passive state.

       

      So, back to the in-depth analysis of the metals in contact with foodstuffs and how these facts relate to alcohol distillation.  For this section I draw heavily on the "Guidelines on Metals and Alloys Used as Food Contact Materials", as published by the World Health Organization 09.03.2001.  The following metallic materials (and others) are covered by these Guidelines: Aluminium, Chromium, Copper, Iron, Lead, Tin, Zinc, Stainless Steel, and  other alloys.  While not a construction material per se, the following metals are also covered because these elements are present as impurities or contaminants in some metallic materials and therefore they can migrate in foodstuffs: Cadmium, Cobalt, and Mercury.  At this juncture it must be stressed that the release of a substance through migration should be reduced as low as is reasonably achievable, not only for health reasons but also to maintain the integrity of the foodstuffs in contact.

       

       

      Aluminium

       

      Aluminium Hydroxide, Al(OH)3, is the most stable form of aluminium under normally benign conditions.  As found in nature it is known as `Gibbsite'.  Closely related are `Aluminium Oxide Hydroxide', AlO(OH), and `Aluminium Oxide', Al2O3.  They differ only by loss of water from the molecule.  These compounds together are the major components of the aluminium ore, `Bauxite'.

       

      Pure aluminium has good machining properties and high ductility.  However its mechanical strength is low.  Therefore, aluminium is often used combined with other metals as alloys (Beliles, 1994).  In general usage, aluminium and its alloys are highly resistant to corrosion (Beliles, 1994).  When exposed to air, the metal develops a thin film of aluminium oxide (AL2O3) almost immediately.  The reaction then slows because the film seals off oxygen, preventing further oxidation or chemical reaction.  The film is colourless, tough and nonflaking.

       

      However, aluminium reacts with acids.  Most dilute acids attack pure aluminium.  At neutral pH, aluminium hydroxide has limited solubility, although the solubility increases markedly at pH below 4.5 and above 8.5 (Elinder and Sjögren, 1986).  Alkaline solutions attack both pure and impure aluminium rapidly and dissolve the metal (Hughes, 1992).

       

       

      Aluminium is widely used in food contact materials such as saucepans, aluminium -lined cooking utensils, coffee pots, and in packaging products such as food-trays, cans, can ends and closures (Elinder and Sjögren, 1986; Codex, 1995).  Aluminium food contact materials are often coated with a resin based coating.

       

      Aluminium alloys for food contact materials may contain alloying elements such as magnesium, silicone, iron, manganese, copper and zinc (European Standard EN 601; European Standard EN 602).  In aluminium cans the production of hydrogen gas from aluminium migration produces an over pressure in the can.

       

      The temperature and storage time is known to influence the migration of aluminium into foodstuff.  In a migration study with 3% acetic acid (Gramiccioni et al., 1989), the migration was approximately 10 fold higher at 40°C compared to 5°C after 24 hours.

       

      In human metabolism, the kidneys excrete aluminium, and only a small amount of aluminium is absorbed (JECFA, 1989).  However, soluble aluminium salts are more easily absorbed.  Patients with impaired renal function treated by dialysis could show a higher aluminium blood level.  In the past, some of these dialyzed patients have shown neurological symptoms of aluminium intoxication due to an inappropriate treatment, which is no longer used.  These symptoms have sometimes been mistaken for those of Alzheimer's disease. WHO (IPCS 1997) has concluded that aluminium is not the origin of Alzheimer's disease.

       

      Conclusions

      Aluminium and its alloys are a poor choice as metals for fabricating distillation equipment.  The metal and its normally protective oxide coating formed by atmospheric exposure are subject to severe attack and migration in all pH conditions save for neutral pH.  As most liquids distilled are normally quite acidic, rapid degradation in the form of corrosion and large-scale pitting can be expected.  To minimize this situation would require careful neutralization of the wash, which has its own inherent problems, particularly if there is any copper further along in the distilling path.  Alcohol distilled under these conditions very often contains undesirable compounds such as the previously-mentioned Schweitzer's Reagent, which will require further processing to eliminate, thus substantially increasing the time and cost of distilling.

       

      If the wash is other than neutral i.e. acidic or alkaline, then metal migration will occur into the wash.  While the metal and its salts may largely remain in the stillpot, undesirable compounds are formed which will appear in the distillate and alter the flavour to something very different to what was expected.  Generally these compounds leave a nasty metallic taste on the palate.  In wood, this taste gets more pronounced as maturation progresses, ruining this batch of spirit.  Any subsequent batches barreled in that cask will also suffer the same fate, as the undesirable compounds permeate the wood and by virtue of alcohol's known ability as a strong solvent, will leach into any new spirit placed therein. 

       

      Rigorous cleaning, perfectly neutral balanced pH wash, meticulous attention to distilling detail, accurate analytical tools e.g. a gas chromatograph, and production of nothing else but flavourless neutral ethanol such as vodka, would be the only practical way to employ aluminium successfully in distilling equipment, i.e. a still.  Given that there are very few amateur distillers with these skills and instruments, or willingness to be limited to a single product, distillation fabricators would be well advised to discard ideas of using aluminium.  Utensils and boilers made from aluminium and its alloys for grain mashing may fare better, however a minimal maintenance, passive metal such as stainless steel would be easily a better option.  There are eminently more suitable metals than aluminium to employ in spirits distilling.

       

       

       

       

      References

      1. ATSDR (1997). Toxicological profile for aluminium. Draft for public comment. U.S.

      Department of Health and Human Services. Public Health Service. Agency for Toxic

      Substances and Disease Registry.

      2. Beliles, R.P. (1994). The metals. In: Patty's Industrial Hygiene and Toxicology, Fourth

      edition, Volume 2, Part C. Edited by Clayton, G.D., and Clayton, F.E. John Wiley & Sons, Inc.

      3. Codex Alimentarius Commission (1995). Doc. no. CX/FAC 96/17. Joint FAO/WHO food standards programme. Codex general standard for contaminants and toxins in foods.

      4. Directive 95/2/EC: European Community. European Parliament and Council Directive on food additives other than colours and sweeteners.

      5. Directive 98/83/EC: Council Directive 98/83/EC of 3 November 1998 on the quality of

      water intended for human consumption.

      6. Elinder and Sjögren (1986). Aluminium. In: Friberg, L., Nordberg, G.F., Vouk, V.B.:

      Handbook on the toxicology of metals. Second edition. Elsevier, Amsterdam, New York,

      Oxford.

      7. European Standard CEN EN 601. Aluminium and aluminium alloys - Castings – Chemical composition of castings for use in contact with food.

      8. European Standard CEN EN 602. Aluminium and aluminium alloys - Wrought products - Chemical composition of semi products used for the fabrication of articles for use in contact with food.

      9. Gramiccioni, L. et al. (1989). An experimental study about aluminium packaged food. In: "Nutritional and Toxicological aspects of food processing". Proceedings of an international symposium, Rome, April 14-16, 1987. Walker, R. and Quattrucci Eds. Taylor & Francis London, p. 331-336.

      10.Gramiccioni, L., Ingrao, G., Milana, M.R., Santaroni, P., Tomassi, G. (1996). Aluminium levels in Italian diets and in selected foods from aluminium utensils. Food Additives and Contaminants. Vol. 13(7) p. 767-774.

      11.Hughes, J.T. (1992). Aluminium and your health. British Library Cataloguing in Publication Data, Rimes House.

      12.IPCS (1997). IPCS report no. 194: Environmental Health Criteria - aluminium. World Health Organization.

      13.JECFA (1989). Evaluation of certain food additives and contaminants. Thirty-third report of the Joint FAO/WHO Expert Committee on Food Additives. World Health Organization, Technical Report Series 776.

      14.Lione, A. (1985). Aluminium toxicology and the aluminium-containing medication.

      Pharmacol. Ther. Vol. 29 p. 225-285.

      15.Liukkonen-Lilja, H. and Piepponen (1992). Leaching of aluminium from aluminium dishes and packages. Food Additives and Contaminants, vol 9(3) p. 213-223.

      16.MAFF (1998). Lead arsenic and other metals in food. Food surveillance paper no. 52. The Stationery Office, London. ISBN 0 11 243041 4.

      17.Mei, L., Yao, T. (1993). Aluminium contamination of food from using aluminium ware. Intern. J. Environ. Anal. Chem. Vol. 50 p. 1-8.

      18.Müller, J.P., Steinegger, A., Schlatter, C. (1993). Contribution of aluminium from packaging materials and cooking utensils to the daily aluminium intake. Z. Lebensm. Unters. Forsch. Vol. 197 p. 332-341.

      19.Nagy, E., Jobst, K. (1994). Aluminium dissolved from kitchen utensils. Bull. Environ. Contam. Toxicol. Vol. 52 9. 396-399.

      20.Pennington, J.A.T., Jones, J.W. (1989). Dietary intake of aluminium. Aluminium and Health – A critical review. Gitelman, p. 67-70.

      21.Pennington, J.A.T., Schoen, S.A. (1995). Estimates of dietary exposure to aluminium. Food additives and contaminants, vol. 12 no. 1, p. 119-128.

      22.WHO (1993). Guidelines for drinking-water quality. volume 1, Recommendations.


      Chromium

       

      Chromium is an essential element to humans.  Chroms, knives, spoons and forks.  Chromium is also used to coat other metals, which are then protected from corrosion because of the passive film which forms on the surface of chromiumium is found at low levels in most materials used as foods.  The main sources of dietary chromium are cereals, meat, vegetables and unrefined sugar, while fish, vegetable oils and fruits contain smaller amounts (Codex, 1995).

       

      Chromium is found in some types of cans and utensils.  In cans it serves to passivate the tinplate surface.  Chromium is used in the production of stainless steel of various kinds and in alloys with iron, nickel and cobalt.  Ferro chromium and chromium metal are the most important classes of chromium used in the alloy industry (Langaard and Norseth, 1986).

       

      Chromium-containing stainless steels (see guideline on stainless steel) are important food contact materials used for transportation, e.g. in milk trucks, for processing equipment, e.g. in the dairy and chocolate industry, in processing of fruit such as apples, grapes, oranges and tomatoes, for containers such as wine tanks, for brew kettles and beer kegs, for processing of dry food such as cereals, flour and sugar, for utensils such as blenders and bread dough mixers, in slaughter-houses, in processing of fish, for nearly all of the equipment in big kitchens, such as restaurants, hospitals, electric kettles, cookware and kitchen appliances of any kind such as sinks and drains, for bowl.

       

      Canned foodstuffs in non-lacquered cans and other processed foodstuffs, particularly acidic foodstuffs such as fruit juices, may be significantly higher in chromium than fresh foodstuffs.  A small contribution to chromium intake can be made by uptake from cans.  However, the significance of this is probably negligible.  Chromium from materials and articles is expected to migrate as Cr(III) and not as Cr(VI) (Guglhofer and Bianchi, 1991).  Cr(III) can not migrate at neutral pH in foodstuffs.  Therefore, the migration of Cr(III) to foods of pH 5 or above is low.  Formation of Cr(VI) as a result of a conversion in water of Cr(III) is not possible.  Therefore, formation of Cr(VI) does not occur in foodstuffs.  This implies, that Cr(VI) is generally not considered to be an issue of food contact materials.  Also, chromium does not migrate significantly from articles made of stainless steel, and any released chromium is Cr(III) (Cunat, 1997).

       

      Due to alloying with chromium, the stainless steels resist corrosion by foods and are readily cleaned, thereby providing hygiene in food preparation and handling. Chromium is one of the metals which naturally forms a corrosion-resistant passive film when in contact with water and air (see section on corrosion).

       

       The specification of chromium is of great importance in determining any possible toxicity issues.  Cr(III), the most stable oxidation state in biological materials, is an essential element for normal glucose metabolism, while Cr(VI) is highly toxic (Beliles, 1994; Costa, 1997; Nordic Council of Ministers, 1995).  Cr(III) has a low toxicity due to low absorption (about 0.5%) (Nordic Council of Ministers,1995).  Toxic aspects of chromium are related to Cr(VI) (Nordic Council of Ministers, 1995), due to its high absorption, easy penetration of the cell membranes and its genotoxicity and oxidising properties (Codex, 1995).


      Conclusions

       

      Chromium as a constituent of Stainless Steel manufacture is perfectly acceptable as a fabrication material in distilling equipment.  Likewise, chromium products where the chromium is in direct contact with the distilling fluid path are very safe.  As to chromium in foodstuffs through migration, even in harsh acidic conditions  below pH 5.0 as commonly found in distilling, it is not considered to be a toxicological problem because the recommended human dietary intake is higher than actual values.  However chromium tubing and other products as made by the electroplating industry for decorative purposes e.g. bath towel rods and hand railings is an entirely different matter when applied to still fabrication.

       

      Decorative chrome-plating is a process whereby a thin layer (sometimes 50 millionths of an inch) of chromium is applied via chromium salts, acids and electricity, to aesthetically enhance (beautify) the  appearance, and/or to prevent tarnishing (staining).  It is usually deposited over a thin base layer of nickel or copper previously deposited over the black iron or steel that the tubing is made from.  To keep costs down the interior of these tubes, not usually seen by the human eye, are prevented from being coated by either the chromium or the copper or nickel.  Consequently the base tubing metal of black iron or steel is exposed to the surrounding environment.  Using these tubing products as still components, while they might look pretty, would place the exposed iron or steel in direct contact with hot fluids.  Thus rapid interior oxidation (rusting) of the tubing and/or contamination of the ethanol product would result.

       

       

       

      References

       

      1. Beliles, R.P. (1994). The metals. In: Patty's Industrial Hygiene and Toxicology, Fourth

      edition, Volume 2, Part C. Edited by Clayton, G.D., and Clayton, F.E. John Wiley & Sons,

      Inc.

      2. Codex Alimentarius Commission (1995). Doc. no. CX/FAC 96/17. Joint FAO/WHO food

      standards programme. Codex general standard for contaminants and toxins in foods.

      3. Costa, M. (1997). Toxicity and carcinogenity of Cr(VI) in animal models and humans. Critical Reviews in Toxicology. 27(5) p. 431-442.

      4. Cunat, P.-J. (1997). Healthy eating and drinking with stainless steel. 1st SS congress,

      Thailand, Dec. 1997.

      5. Guglhofer, J., Bianchi, V. (1991). Metals and their compounds in the environment. VCH

      Verlag, Weinheim, Germany.

      6. Florence, T.M., Batley, G.E. (1980). Chemical speciation in natural waters. CRC Critical

      Reviews in Analytical chemistry. p. 219-296.

      7. Langaard, S., Norseth, T. (1986). Chromium. In: Friberg, L., Nordberg, G.F., Vouk, V.B.

      Handbook on the toxicology of metals. Second edition. Elsevier, Amsterdam, New York,

      Oxford.

      8. Nordic Council of Ministers (1995). Risk evaluation of essential trace elements - essential

      versus toxic levels of intake. Report of a Nordic project group. Ed.: Oskarsson, A. Nordic

      Council of Ministers, Copenhagen, Denmark.

      9. SCF (1993). Report of the Scientific Committee for food (thirty-first series). Nutrient and

      energy intakes for the European Community.

      10. Veien, N.K., Hattel, T., Laurberg, G. (1994). Chromate-allergic patients challenged orally

      with potassium dichromate. Contact dermatitis. 31 p. 137-139.

      11.WHO (1993). Guidelines for drinking-water quality. Volume 1. Recommendations.


      Copper

       

      Copper exists in two oxidation states: Cu(I) (cuprous) and Cu(II) (cupric). Copper can also occur in a trivalent state due to certain chemical reactions.  Copper is among the most effective of metal biochemical oxidising agents. Copper is an essential element to man (Aaseth and Norseth, 1986). Copper also has the ability to restrict bacterial growth, e.g. Legionella, in drinking water systems (Rogers et al., 1994).

       

      Copper is naturally present in most foodstuffs in the form of copper ions or copper salts (Codex, 1995).  The main sources are meat, offal, fish, pecans, milk chocolate and green vegetables (Aaseth and Norseth, 1986).

       

      Copper vessels are traditionally used in many specialised food processing activities, such as breweries and distilleries, for cheese-making, chocolate, dry vegetables, jam and sweets production.  In food utensils, copper is in general used unalloyed, for exam ple in saucepans, which are usually lined inside with tin or stainless steel. Copper is used in alloys, particularly brass, bronze, and nickel silver (British Non-Ferrous Metals Federation, 1997).

       

      Copper is slowly attacked by dilute hydrochloric acid or dilute sulfuric acid and is soluble in ammonia water (Beliles, 1994).  Acidic foodstuffs can attack copper in utensils. Therefore, copper may be present in foodstuffs due to migration from food contact materials, e.g. copper utensils, copper pipes, etc. (Codex, 1995) or from using drinking water from copper pipes for food preparation.  In some cases, high copper migration might induce some discoloration.  Migration from copper into sugar confectionery cooked at 125-140 °C and at pH 5.1-6.0 on average increases the copper concentration in the confectionery from 0.13 mg/kg to 0.25 mg/kg (Written comments from BCCCA, 1999).

       

      Copper is one of the best conductors of heat available.  Only silver has a higher thermal conductivity, while stainless steel is a relatively mediocre conductor. (Hypertextbook Physics, 2006).

       

       

      Conclusions

       

      The level of contamination of copper observed in drinking water and foodstuffs does not constitute a safety problem.  There is a greater risk of adverse health effects from copper deficiency, than from excessive copper intake.

       

      Copper has been employed for centuries as the metal of choice in distilling equipment, particularly in still fabrication.  This was originally due to its abundance, its malleability using simple hand tools, and its superior heat transfer capabilities over other metals.  Later, when more modern metals such as stainless steels became widely available, it was discovered by accident that these metals produced a different and clearly inferior spirit to that produced from the same mash employed in copper stills.

       

      The cause of this anomaly was proven to be stainless steel's inert nature, which allowed the spirit vapour to pass unaltered, whereas copper reacts with any sulphides (rotten egg gases) which are always present in grain mashes and removes them from the distillate as sulphates and sulphites.  Consequently traditional distillers like the Scottish and Irish Whisk(e)y producers rapidly went back to using copper.  Today you will see stainless steel used in mash tuns and transfer piping, but in the stills themselves where the ethanolic vapours destined to become potable spirits are separated from the water, copper is the fabrication metal.

       

       

      References

      1. Aaseth, J., Norseth, T. (1986). Copper. In: Friberg, L., Nordberg, G.F., Vouk, V.B. Handbook on the toxicology of metals. Second edition. Elsevier, Amsterdam, New York, Oxford.

      2. Beliles, R.P. (1994). The metals. In: Patty's Industrial Hygiene and Toxicology, Fourth

      edition, Volume 2, Part C. Edited by Clayton, G.D., and Clayton, F.E. John Wiley & Sons, Inc.

      3. British Non-Ferrous Metals Federation (1997). Written comments on the draft guideline.

      4. Codex Alimentarius Commission (1995). Doc. no. CX/FAC 96/17. Joint FAO/WHO food standards programme. Codex general standard for contaminants and toxins in foods.

      5. Environmental Health Criteria for Copper (1996). PCS/EHC 96.28 unedited, page 9.

      6. IPCS EHC 200 Copper (1998). Environmental Health Criteria 200. World Health

      Organization, Geneva.

      7. JECFA (1982). Evaluation of certain food additives and contaminants. Twenty-sixth report of the Joint FAO/WHO Expert Committee on Food Additives. World Health Organization,

      Technical Report Series 683.

      8. Rogers, J., Dowsett, A.B., Dennis, P.J., Lee, J.V., Keevil, C.W. (1994). Influence of plumbing materials on bio film formation and growth of Lagionella pneumophila in notable water systems. Appl. Environ. Microbiol. p. 1842-1851.

      9. SCF (1993). Reports of the Scientific Committee for Food. Thirty-first series. Nutrient and energy intakes for the European Community.

      10. WHO (1998). Guidelines for drinking-water quality. Addendum to Volume 1,

      Recommendations.

      11. Online http://hypertextbook.com/physics/thermal/conduction/ as retrieved on 8 Mar 2006 1:36:26 GMT

       

    • duds2u
      Well done Harry, I think this should compulsory reading for all newcomers to the craft of distillng, particularly those who intend building their own still.
      Message 2 of 5 , May 27, 2006
      • 0 Attachment
        Well done Harry,
        I think this should compulsory reading for all newcomers to the
        craft of distillng, particularly those who intend building their own
        still.
        Cheers
        Mal
        --- In Distillers@yahoogroups.com, "Harry" <gnikomson2000@...> wrote:
        >
        > As promised, the first draft of the metals paper. It is
        incomplete, and
        > remains a 'work in progress', subject to alteration without
        notice.
        > However there should be enough info in it to give some food for
        thought,
        > which is what the 'spirit' of this group is about (hopefully). It
        is a
        > long dissertation, so feel free to read, save or discard as you
        see fit.
        > Slainte! regards Harry
        >
        > Chapter 03 - Metals
        > > >
        >
        > From time to time, the subject comes up of `what metals can or
        > can't be used in distilling equipment'. A very simple and safe
        > rule of thumb is this: for contact with alcohol or its feedstock,
        never
        > use any metal that is not used in commercial distilleries for that
        stage
        > of processing. While this may be the easiest approach, it tells
        you
        > very little about why this or that metal is acceptable or not. Any
        > distiller worth his salt should know exactly why a particular
        material
        > or procedure is employed. Therefore a more complete analysis is in
        > order.
        >
        > > >
        >
        > As a starting point, let's take a look at the metals in commercial
        > distilling plants. Black iron, cast iron, galvanized iron, steel,
        > stainless steel, copper, chromium, aluminium, lead, zinc, nickel,
        brass,
        > various alloys, and several other metals in smaller proportions
        are all
        > found somewhere in a distillery. That does not mean they should
        all be
        > used in the distillation process. On the contrary, most of the
        > aforementioned metals are found in the construction of buildings,
        > peripheral and non-critical machinery. For the distilling process
        > proper, where alcohol and vapours are being manipulated, there are
        only
        > four acceptable metals to use, namely silver, copper, treated
        brass, and
        > stainless steel. The reasons why will become clear as you read
        further.
        >
        > > >
        >
        > Beverage alcohol and the feedstock it is derived from are classed
        as
        > foods meant for human consumption. Grains, fruits, sugars, ethanol
        > liquid and vapours, and yeasts; all are categorized as foodstuffs.
        > There are very strict rules and regulations governing what
        materials are
        > allowed to come in contact with foods during processing, storage
        and
        > packaging. These regulations have been formulated after many
        years of
        > rigorous testing of materials and their influence on the foods in
        > question and/or the affects they have on human metabolism. Many
        > countries adopt the policies of International monitoring bodies
        such as
        > the World Health Organization (WHO). This body has published
        > information and recommendations for the materials likely to come
        into
        > contact with foods.
        >
        > > >
        >
        > Like many substances in common usage, the pH of foodstuffs plays an
        > important role in determining which metals are suitable for food
        > contact. Whether a food is acidic, such as tomatoes and soft
        fruits, or
        > neutral or (less common) basic, has a marked influence on the
        types of
        > metals and other materials such as plastics that can be allowed for
        > processing and storage. The temperature of the foodstuff also
        plays a
        > part in determining suitability or otherwise as many foods when
        hot have
        > accelerated reactions in contact with metals. It should be noted
        here
        > that commercial processing and domestic or household usage of
        materials
        > for food contact are two separate situations. In a commercial
        > distillery, everything is subject to regulations regarding
        suitability,
        > safety, and consumer protection and well-being. There are no such
        > safeguards for household usage, save for commonsense and `current
        > practice' methodology. However, as I intimated earlier, a hobby
        > distiller should at least try to follow the practices of commercial
        > processing. Therein lies safety and relative peace of mind.
        >
        > > >
        >
        > The reaction of a metal in contact with foodstuffs is a selection
        > criteria used predominately to avoid metal corrosion and mechanical
        > failure, necessitating costly replacement of equipment. Mashes or
        > `worts' will almost always be acidic, as it is a requirement of
        > yeast to have an acidic environment to perform its functions of
        > producing ethanol and other desirable substances. Mashes
        fermented by
        > yeasts tend to become more acidic as the fermentation progresses.
        Thus
        > the completed wash or `beer' will have a pH of nominally 4.0 or
        > even lower. When fermentation is finished, this acidic beer is now
        > charged to the still and heated. Elementary school chemistry
        teaches
        > that hot acids are extremely corrosive to certain metals, notably
        > aluminium, black iron, certain steels and tin. For this reason
        alone,
        > the aforementioned metals are not really suitable for stillpots,
        boilers
        > or re-boilers, unless of course you like the idea of frequently
        > replacing components of your still. You will note this corrosion
        > resistivity is a separate issue and has nothing to do with possible
        > metal migration into the foodstuff or chemical reactions that may
        form
        > undesirable substances in the wash. That is a selection criterion
        > we'll look at later.
        >
        > > >
        >
        > Regardless of regulations, commonsense tells you that all still
        parts
        > likely to come into contact with hot acidic liquids and vapours
        should
        > be made from a material relatively impervious to corrosion, heat,
        and
        > toxic leaching of chemicals. Copper, food-grade or Austenitic
        stainless
        > steel (304 & 316), and correctly treated brass fill this role
        admirably.
        > I will deal with each in turn, but while we're on the subject of
        > `treated' metals I should make mention of two other metals
        > sometimes considered by the unwary, namely Tin or Tinplate, and
        > Galvanized Iron.
        >
        > > >
        >
        > Easily corroded metals such as Black Iron are often coated with a
        > surface layer of chemicals or other metals to protect the base
        metal
        > from corrosion. What is not understood by many people is that the
        > composite material is meant to be used in normal everyday use, not
        in
        > harsh chemical processing environments. The galvanizing on the
        surface
        > of the Iron contains Zinc, which is a toxic metal that leaches
        badly
        > under hot acidic conditions. The Zinc is rapidly eaten away and
        > finishes up in the distillate. The base Iron is then exposed to
        the
        > acidic wash, resulting in corrosion (rust), which also gets into
        the
        > processing chain. The stillpot wears out very quickly and needs
        to be
        > replaced frequently. Galvanized Iron has no place in process
        distilling
        > of foodstuffs such as beverage alcohol.
        >
        > > >
        >
        > Similarly, Tin is attacked by both acids and bases (alkali) but
        has the
        > curious property of being relatively stable under neutral pH
        conditions.
        > For this reason, it was commonly used in centuries past as an
        > alternative to copper. However to use Tin, the stillman had to be
        sure
        > the wash was brought to a neutral pH condition, not always an easy
        thing
        > to do given the crude and inaccurate measuring instruments and
        methods
        > (or lack thereof) employed in bygone eras. It is a source of much
        > confusion when the distillers of old tell the young folk "You gotta
        > neutralise the beer". So `young pistol' follows this sage
        > advice and adds Sodium Bicarbonate (a neutralising buffer, pH 8.5)
        to
        > the beer in his brand new copper potstill (tinplate has been
        largely
        > superseded). Then he gets the fright of his life when the
        distillate
        > runs with a pretty bright blue colour. The blue is, of course, the
        > well-known Cuprous Hydroxide or Schweitzer's Reagent, formed by a
        > complex chemical reaction triggered by the neutral-to-alkaline
        > conditions set up in the Copper still by the S. Bicarbonate. If
        Tin
        > were the construction material used, there would be no such
        reaction.
        >
        > > >
        >
        > One must always use caution when evaluating procedures from the
        past.
        > Manufacturers from every era strive to refine their processes
        based on
        > the materials and knowledge at hand. However time marches on, and
        > advances in Science & Technology march right along with it.
        >
        > > >
        >
        > > >
        >
        > Corrosion of Metals
        >
        > > >
        >
        > The biggest problem with most metals in distilling, or indeed most
        > processing-type applications, is corrosion. Often it is the
        deciding
        > factor when weighing up the suitability of a metal for a particular
        > duty. It is the driving force behind mankind's quest for newer and
        > more durable metal alloys.
        >
        > > >
        >
        > > >
        >
        > Corrosion occurs when the exposed metal surface reacts
        electrochemically
        > with the surrounding medium in the presence of moisture and
        oxygen.
        > This reaction results in the formation of surface compounds of the
        metal
        > (e.g. hydroxides). The rate at which corrosion proceeds will
        depend in
        > part on the composition of the aqueous medium. Corrosion of iron
        in
        > very pure water will be considerably slower than in water
        containing
        > acids or salts.
        >
        > > >
        >
        > The rate of corrosion depends also on the solubility of the formed
        > compounds in the medium, and their rate of removal. Thus the
        formed
        > compounds may be removed rapidly in a flowing aqueous medium, and
        the
        > corrosion rate will be high (thinning of the walls of water
        pipes). In
        > a static medium, the rate of corrosion will be moderated as the
        ionic
        > concentration of the surrounding medium increases.
        >
        > > >
        >
        > Corrosion products formed in the atmosphere are more or less
        adherent
        > e.g. rust on iron, verdigris on copper. Rust is essentially
        hydrated
        > ferric oxide which usually also contains some ferrous oxide and may
        > contain iron carbonates and/or sulfates. The equivalent in copper
        is
        > verdigris, consisting mainly of basic copper carbonate, but may
        also
        > contain copper sulfates and chlorides. However, rust forms loose
        scale
        > and is easily removed, while verdigris forms a stable patina on the
        > Copper surface.
        >
        > > >
        >
        > > >
        >
        > Corrosion resistance
        >
        > > >
        >
        > Some metals (e.g. aluminium, chromium) are rendered "passive" (very
        > resistant to corrosion) by the spontaneous formation, in the
        presence of
        > oxygen, of an invisible and impermeable oxide film a few Angstrom
        units
        > (0.1 nanometers) thick. This passive layer is very strong, very
        adherent
        > and self-repairing if it is damaged. One of the main reasons for
        the
        > production and use of metallic alloys is that alloys are virtually
        > always more resistant to corrosion than are their basic metal
        > components.
        >
        > > >
        >
        > This is partly due to the fact that migration of the constituent
        > elements is much lower than migration from non-alloyed metals,
        because
        > of the micro-structural binding of the elements within the alloys.
        > Stainless steels, which are alloys of iron with a minimum of 10.5%
        > chromium, are orders of magnitude more resistant to corrosion than
        iron
        > itself. This is partly because they possess the general
        properties of
        > alloys, referred to above, but mainly because they have a surface
        > "passive film" which is naturally and rapidly formed on contact
        with the
        > oxygen in air or water. Stainless steels used in food contact
        > applications are invariably used in the passive state.
        >
        > > >
        >
        > So, back to the in-depth analysis of the metals in contact with
        > foodstuffs and how these facts relate to alcohol distillation.
        For this
        > section I draw heavily on the "Guidelines on Metals and Alloys Used
        > as Food Contact Materials", as published by the World Health
        > Organization 09.03.2001. The following metallic materials (and
        others)
        > are covered by these Guidelines: Aluminium, Chromium, Copper, Iron,
        > Lead, Tin, Zinc, Stainless Steel, and other alloys. While not a
        > construction material per se, the following metals are also covered
        > because these elements are present as impurities or contaminants
        in some
        > metallic materials and therefore they can migrate in foodstuffs:
        > Cadmium, Cobalt, and Mercury. At this juncture it must be
        stressed that
        > the release of a substance through migration should be reduced as
        low as
        > is reasonably achievable, not only for health reasons but also to
        > maintain the integrity of the foodstuffs in contact.
        >
        > > >
        >
        > > >
        >
        > Aluminium
        >
        > > >
        >
        > Aluminium Hydroxide, Al(OH)3, is the most stable form of aluminium
        under
        > normally benign conditions. As found in nature it is known as
        > `Gibbsite'. Closely related are `Aluminium Oxide
        > Hydroxide', AlO(OH), and `Aluminium Oxide', Al2O3. They
        > differ only by loss of water from the molecule. These compounds
        > together are the major components of the aluminium ore,
        > `Bauxite'.
        >
        > > >
        >
        > Pure aluminium has good machining properties and high ductility.
        > However its mechanical strength is low. Therefore, aluminium is
        often
        > used combined with other metals as alloys (Beliles, 1994). In
        general
        > usage, aluminium and its alloys are highly resistant to corrosion
        > (Beliles, 1994). When exposed to air, the metal develops a thin
        film of
        > aluminium oxide (AL2O3) almost immediately. The reaction then
        slows
        > because the film seals off oxygen, preventing further oxidation or
        > chemical reaction. The film is colourless, tough and nonflaking.
        >
        > > >
        >
        > However, aluminium reacts with acids. Most dilute acids attack
        pure
        > aluminium. At neutral pH, aluminium hydroxide has limited
        solubility,
        > although the solubility increases markedly at pH below 4.5 and
        above 8.5
        > (Elinder and Sjögren, 1986). Alkaline solutions attack both pure
        and
        > impure aluminium rapidly and dissolve the metal (Hughes, 1992).
        >
        > > >
        >
        > > >
        >
        > Aluminium is widely used in food contact materials such as
        saucepans,
        > aluminium -lined cooking utensils, coffee pots, and in packaging
        > products such as food-trays, cans, can ends and closures (Elinder
        and
        > Sjögren, 1986; Codex, 1995). Aluminium food contact materials are
        > often coated with a resin based coating.
        >
        > > >
        >
        > Aluminium alloys for food contact materials may contain alloying
        > elements such as magnesium, silicone, iron, manganese, copper and
        zinc
        > (European Standard EN 601; European Standard EN 602). In
        aluminium cans
        > the production of hydrogen gas from aluminium migration produces
        an over
        > pressure in the can.
        >
        > > >
        >
        > The temperature and storage time is known to influence the
        migration of
        > aluminium into foodstuff. In a migration study with 3% acetic acid
        > (Gramiccioni et al., 1989), the migration was approximately 10 fold
        > higher at 40°C compared to 5°C after 24 hours.
        >
        >
        >
        > In human metabolism, the kidneys excrete aluminium, and only a
        small
        > amount of aluminium is absorbed (JECFA, 1989). However, soluble
        > aluminium salts are more easily absorbed. Patients with impaired
        renal
        > function treated by dialysis could show a higher aluminium blood
        level.
        > In the past, some of these dialyzed patients have shown
        neurological
        > symptoms of aluminium intoxication due to an inappropriate
        treatment,
        > which is no longer used. These symptoms have sometimes been
        mistaken
        > for those of Alzheimer's disease. WHO (IPCS 1997) has concluded
        that
        > aluminium is not the origin of Alzheimer's disease.
        >
        > > >
        >
        > Conclusions
        >
        > Aluminium and its alloys are a poor choice as metals for
        fabricating
        > distillation equipment. The metal and its normally protective
        oxide
        > coating formed by atmospheric exposure are subject to severe
        attack and
        > migration in all pH conditions save for neutral pH. As most
        liquids
        > distilled are normally quite acidic, rapid degradation in the form
        of
        > corrosion and large-scale pitting can be expected. To minimize
        this
        > situation would require careful neutralization of the wash, which
        has
        > its own inherent problems, particularly if there is any copper
        further
        > along in the distilling path. Alcohol distilled under these
        conditions
        > very often contains undesirable compounds such as the
        > previously-mentioned Schweitzer's Reagent, which will require
        > further processing to eliminate, thus substantially increasing the
        time
        > and cost of distilling.
        >
        > > >
        >
        > If the wash is other than neutral i.e. acidic or alkaline, then
        metal
        > migration will occur into the wash. While the metal and its salts
        may
        > largely remain in the stillpot, undesirable compounds are formed
        which
        > will appear in the distillate and alter the flavour to something
        very
        > different to what was expected. Generally these compounds leave a
        nasty
        > metallic taste on the palate. In wood, this taste gets more
        pronounced
        > as maturation progresses, ruining this batch of spirit. Any
        subsequent
        > batches barreled in that cask will also suffer the same fate, as
        the
        > undesirable compounds permeate the wood and by virtue of alcohol's
        > known ability as a strong solvent, will leach into any new spirit
        placed
        > therein.
        >
        > > >
        >
        > Rigorous cleaning, perfectly neutral balanced pH wash, meticulous
        > attention to distilling detail, accurate analytical tools e.g. a
        gas
        > chromatograph, and production of nothing else but flavourless
        neutral
        > ethanol such as vodka, would be the only practical way to employ
        > aluminium successfully in distilling equipment, i.e. a still.
        Given
        > that there are very few amateur distillers with these skills and
        > instruments, or willingness to be limited to a single product,
        > distillation fabricators would be well advised to discard ideas of
        using
        > aluminium. Utensils and boilers made from aluminium and its
        alloys for
        > grain mashing may fare better, however a minimal maintenance,
        passive
        > metal such as stainless steel would be easily a better option.
        There
        > are eminently more suitable metals than aluminium to employ in
        spirits
        > distilling.
        >
        > > >
        >
        > > >
        >
        > > >
        >
        > > >
        >
        > References
        >
        > 1. ATSDR (1997). Toxicological profile for aluminium. Draft for
        public
        > comment. U.S.
        >
        > Department of Health and Human Services. Public Health Service.
        Agency
        > for Toxic
        >
        > Substances and Disease Registry.
        >
        > 2. Beliles, R.P. (1994). The metals. In: Patty's Industrial Hygiene
        > and Toxicology, Fourth
        >
        > edition, Volume 2, Part C. Edited by Clayton, G.D., and Clayton,
        F.E.
        > John Wiley & Sons, Inc.
        >
        > 3. Codex Alimentarius Commission (1995). Doc. no. CX/FAC 96/17.
        Joint
        > FAO/WHO food standards programme. Codex general standard for
        > contaminants and toxins in foods.
        >
        > 4. Directive 95/2/EC: European Community. European Parliament and
        > Council Directive on food additives other than colours and
        sweeteners.
        >
        > 5. Directive 98/83/EC: Council Directive 98/83/EC of 3 November
        1998 on
        > the quality of
        >
        > water intended for human consumption.
        >
        > 6. Elinder and Sjögren (1986). Aluminium. In: Friberg, L.,
        Nordberg,
        > G.F., Vouk, V.B.:
        >
        > Handbook on the toxicology of metals. Second edition. Elsevier,
        > Amsterdam, New York,
        >
        > Oxford.
        >
        > 7. European Standard CEN EN 601. Aluminium and aluminium alloys -
        > Castings – Chemical composition of castings for use in contact with
        > food.
        >
        > 8. European Standard CEN EN 602. Aluminium and aluminium alloys -
        > Wrought products - Chemical composition of semi products used for
        the
        > fabrication of articles for use in contact with food.
        >
        > 9. Gramiccioni, L. et al. (1989). An experimental study about
        aluminium
        > packaged food. In: "Nutritional and Toxicological aspects of food
        > processing". Proceedings of an international symposium, Rome, April
        > 14-16, 1987. Walker, R. and Quattrucci Eds. Taylor & Francis
        London, p.
        > 331-336.
        >
        > 10.Gramiccioni, L., Ingrao, G., Milana, M.R., Santaroni, P.,
        Tomassi, G.
        > (1996). Aluminium levels in Italian diets and in selected foods
        from
        > aluminium utensils. Food Additives and Contaminants. Vol. 13(7) p.
        > 767-774.
        >
        > 11.Hughes, J.T. (1992). Aluminium and your health. British Library
        > Cataloguing in Publication Data, Rimes House.
        >
        > 12.IPCS (1997). IPCS report no. 194: Environmental Health
        Criteria -
        > aluminium. World Health Organization.
        >
        > 13.JECFA (1989). Evaluation of certain food additives and
        contaminants.
        > Thirty-third report of the Joint FAO/WHO Expert Committee on Food
        > Additives. World Health Organization, Technical Report Series 776.
        >
        > 14.Lione, A. (1985). Aluminium toxicology and the aluminium-
        containing
        > medication.
        >
        > Pharmacol. Ther. Vol. 29 p. 225-285.
        >
        > 15.Liukkonen-Lilja, H. and Piepponen (1992). Leaching of aluminium
        from
        > aluminium dishes and packages. Food Additives and Contaminants,
        vol 9(3)
        > p. 213-223.
        >
        > 16.MAFF (1998). Lead arsenic and other metals in food. Food
        surveillance
        > paper no. 52. The Stationery Office, London. ISBN 0 11 243041 4.
        >
        > 17.Mei, L., Yao, T. (1993). Aluminium contamination of food from
        using
        > aluminium ware. Intern. J. Environ. Anal. Chem. Vol. 50 p. 1-8.
        >
        > 18.Müller, J.P., Steinegger, A., Schlatter, C. (1993). Contribution
        > of aluminium from packaging materials and cooking utensils to the
        daily
        > aluminium intake. Z. Lebensm. Unters. Forsch. Vol. 197 p. 332-341.
        >
        > 19.Nagy, E., Jobst, K. (1994). Aluminium dissolved from kitchen
        > utensils. Bull. Environ. Contam. Toxicol. Vol. 52 9. 396-399.
        >
        > 20.Pennington, J.A.T., Jones, J.W. (1989). Dietary intake of
        aluminium.
        > Aluminium and Health – A critical review. Gitelman, p. 67-70.
        >
        > 21.Pennington, J.A.T., Schoen, S.A. (1995). Estimates of dietary
        > exposure to aluminium. Food additives and contaminants, vol. 12
        no. 1,
        > p. 119-128.
        >
        > 22.WHO (1993). Guidelines for drinking-water quality. volume 1,
        > Recommendations.
        >
        >
        > Chromium
        >
        > > >
        >
        > Chromium is an essential element to humans. Chroms, knives,
        spoons and
        > forks. Chromium is also used to coat other metals, which are then
        > protected from corrosion because of the passive film which forms
        on the
        > surface of chromiumium is found at low levels in most materials
        used as
        > foods. The main sources of dietary chromium are cereals, meat,
        > vegetables and unrefined sugar, while fish, vegetable oils and
        fruits
        > contain smaller amounts (Codex, 1995).
        >
        > > >
        >
        > Chromium is found in some types of cans and utensils. In cans it
        serves
        > to passivate the tinplate surface. Chromium is used in the
        production
        > of stainless steel of various kinds and in alloys with iron,
        nickel and
        > cobalt. Ferro chromium and chromium metal are the most important
        > classes of chromium used in the alloy industry (Langaard and
        Norseth,
        > 1986).
        >
        > > >
        >
        > Chromium-containing stainless steels (see guideline on stainless
        steel)
        > are important food contact materials used for transportation, e.g.
        in
        > milk trucks, for processing equipment, e.g. in the dairy and
        chocolate
        > industry, in processing of fruit such as apples, grapes, oranges
        and
        > tomatoes, for containers such as wine tanks, for brew kettles and
        beer
        > kegs, for processing of dry food such as cereals, flour and sugar,
        for
        > utensils such as blenders and bread dough mixers, in slaughter-
        houses,
        > in processing of fish, for nearly all of the equipment in big
        kitchens,
        > such as restaurants, hospitals, electric kettles, cookware and
        kitchen
        > appliances of any kind such as sinks and drains, for bowl.
        >
        > > >
        >
        > Canned foodstuffs in non-lacquered cans and other processed
        foodstuffs,
        > particularly acidic foodstuffs such as fruit juices, may be
        > significantly higher in chromium than fresh foodstuffs. A small
        > contribution to chromium intake can be made by uptake from cans.
        > However, the significance of this is probably negligible.
        Chromium from
        > materials and articles is expected to migrate as Cr(III) and not as
        > Cr(VI) (Guglhofer and Bianchi, 1991). Cr(III) can not migrate at
        > neutral pH in foodstuffs. Therefore, the migration of Cr(III) to
        foods
        > of pH 5 or above is low. Formation of Cr(VI) as a result of a
        > conversion in water of Cr(III) is not possible. Therefore,
        formation of
        > Cr(VI) does not occur in foodstuffs. This implies, that Cr(VI) is
        > generally not considered to be an issue of food contact materials.
        > Also, chromium does not migrate significantly from articles made of
        > stainless steel, and any released chromium is Cr(III) (Cunat,
        1997).
        >
        > > >
        >
        > Due to alloying with chromium, the stainless steels resist
        corrosion by
        > foods and are readily cleaned, thereby providing hygiene in food
        > preparation and handling. Chromium is one of the metals which
        naturally
        > forms a corrosion-resistant passive film when in contact with
        water and
        > air (see section on corrosion).
        >
        > > >
        >
        > The specification of chromium is of great importance in
        determining any
        > possible toxicity issues. Cr(III), the most stable oxidation
        state in
        > biological materials, is an essential element for normal glucose
        > metabolism, while Cr(VI) is highly toxic (Beliles, 1994; Costa,
        1997;
        > Nordic Council of Ministers, 1995). Cr(III) has a low toxicity
        due to
        > low absorption (about 0.5%) (Nordic Council of Ministers,1995).
        Toxic
        > aspects of chromium are related to Cr(VI) (Nordic Council of
        Ministers,
        > 1995), due to its high absorption, easy penetration of the cell
        > membranes and its genotoxicity and oxidising properties (Codex,
        1995).
        >
        >
        > Conclusions
        >
        > > >
        >
        > Chromium as a constituent of Stainless Steel manufacture is
        perfectly
        > acceptable as a fabrication material in distilling equipment.
        Likewise,
        > chromium products where the chromium is in direct contact with the
        > distilling fluid path are very safe. As to chromium in foodstuffs
        > through migration, even in harsh acidic conditions below pH 5.0 as
        > commonly found in distilling, it is not considered to be a
        toxicological
        > problem because the recommended human dietary intake is higher than
        > actual values. However chromium tubing and other products as made
        by
        > the electroplating industry for decorative purposes e.g. bath
        towel rods
        > and hand railings is an entirely different matter when applied to
        still
        > fabrication.
        >
        > > >
        >
        > Decorative chrome-plating is a process whereby a thin layer
        (sometimes
        > 50 millionths of an inch) of chromium is applied via chromium
        salts,
        > acids and electricity, to aesthetically enhance (beautify) the
        > appearance, and/or to prevent tarnishing (staining). It is usually
        > deposited over a thin base layer of nickel or copper previously
        > deposited over the black iron or steel that the tubing is made
        from. To
        > keep costs down the interior of these tubes, not usually seen by
        the
        > human eye, are prevented from being coated by either the chromium
        or the
        > copper or nickel. Consequently the base tubing metal of black
        iron or
        > steel is exposed to the surrounding environment. Using these
        tubing
        > products as still components, while they might look pretty, would
        place
        > the exposed iron or steel in direct contact with hot fluids. Thus
        rapid
        > interior oxidation (rusting) of the tubing and/or contamination of
        the
        > ethanol product would result.
        >
        > > >
        >
        > > >
        >
        > > >
        >
        > References
        >
        > > >
        >
        > 1. Beliles, R.P. (1994). The metals. In: Patty's Industrial Hygiene
        > and Toxicology, Fourth
        >
        > edition, Volume 2, Part C. Edited by Clayton, G.D., and Clayton,
        F.E.
        > John Wiley & Sons,
        >
        > Inc.
        >
        > 2. Codex Alimentarius Commission (1995). Doc. no. CX/FAC 96/17.
        Joint
        > FAO/WHO food
        >
        > standards programme. Codex general standard for contaminants and
        toxins
        > in foods.
        >
        > 3. Costa, M. (1997). Toxicity and carcinogenity of Cr(VI) in animal
        > models and humans. Critical Reviews in Toxicology. 27(5) p. 431-
        442.
        >
        > 4. Cunat, P.-J. (1997). Healthy eating and drinking with stainless
        > steel. 1st SS congress,
        >
        > Thailand, Dec. 1997.
        >
        > 5. Guglhofer, J., Bianchi, V. (1991). Metals and their compounds
        in the
        > environment. VCH
        >
        > Verlag, Weinheim, Germany.
        >
        > 6. Florence, T.M., Batley, G.E. (1980). Chemical speciation in
        natural
        > waters. CRC Critical
        >
        > Reviews in Analytical chemistry. p. 219-296.
        >
        > 7. Langaard, S., Norseth, T. (1986). Chromium. In: Friberg, L.,
        > Nordberg, G.F., Vouk, V.B.
        >
        > Handbook on the toxicology of metals. Second edition. Elsevier,
        > Amsterdam, New York,
        >
        > Oxford.
        >
        > 8. Nordic Council of Ministers (1995). Risk evaluation of essential
        > trace elements - essential
        >
        > versus toxic levels of intake. Report of a Nordic project group.
        Ed.:
        > Oskarsson, A. Nordic
        >
        > Council of Ministers, Copenhagen, Denmark.
        >
        > 9. SCF (1993). Report of the Scientific Committee for food (thirty-
        first
        > series). Nutrient and
        >
        > energy intakes for the European Community.
        >
        > 10. Veien, N.K., Hattel, T., Laurberg, G. (1994). Chromate-allergic
        > patients challenged orally
        >
        > with potassium dichromate. Contact dermatitis. 31 p. 137-139.
        >
        > 11.WHO (1993). Guidelines for drinking-water quality. Volume 1.
        > Recommendations.
        >
        >
        > Copper
        >
        > > >
        >
        > Copper exists in two oxidation states: Cu(I) (cuprous) and Cu(II)
        > (cupric). Copper can also occur in a trivalent state due to certain
        > chemical reactions. Copper is among the most effective of metal
        > biochemical oxidising agents. Copper is an essential element to man
        > (Aaseth and Norseth, 1986). Copper also has the ability to restrict
        > bacterial growth, e.g. Legionella, in drinking water systems
        (Rogers et
        > al., 1994).
        >
        > > >
        >
        > Copper is naturally present in most foodstuffs in the form of
        copper
        > ions or copper salts (Codex, 1995). The main sources are meat,
        offal,
        > fish, pecans, milk chocolate and green vegetables (Aaseth and
        Norseth,
        > 1986).
        >
        > > >
        >
        > Copper vessels are traditionally used in many specialised food
        > processing activities, such as breweries and distilleries, for
        > cheese-making, chocolate, dry vegetables, jam and sweets
        production. In
        > food utensils, copper is in general used unalloyed, for exam ple in
        > saucepans, which are usually lined inside with tin or stainless
        steel.
        > Copper is used in alloys, particularly brass, bronze, and nickel
        silver
        > (British Non-Ferrous Metals Federation, 1997).
        >
        > > >
        >
        > Copper is slowly attacked by dilute hydrochloric acid or dilute
        sulfuric
        > acid and is soluble in ammonia water (Beliles, 1994). Acidic
        foodstuffs
        > can attack copper in utensils. Therefore, copper may be present in
        > foodstuffs due to migration from food contact materials, e.g.
        copper
        > utensils, copper pipes, etc. (Codex, 1995) or from using drinking
        water
        > from copper pipes for food preparation. In some cases, high copper
        > migration might induce some discoloration. Migration from copper
        into
        > sugar confectionery cooked at 125-140 °C and at pH 5.1-6.0 on
        average
        > increases the copper concentration in the confectionery from 0.13
        mg/kg
        > to 0.25 mg/kg (Written comments from BCCCA, 1999).
        >
        > > >
        >
        > Copper is one of the best conductors of heat available. Only
        silver has
        > a higher thermal conductivity, while stainless steel is a
        relatively
        > mediocre conductor. (Hypertextbook Physics, 2006).
        >
        > > >
        >
        > > >
        >
        > Conclusions
        >
        > > >
        >
        > The level of contamination of copper observed in drinking water and
        > foodstuffs does not constitute a safety problem. There is a
        greater
        > risk of adverse health effects from copper deficiency, than from
        > excessive copper intake.
        >
        > > >
        >
        > Copper has been employed for centuries as the metal of choice in
        > distilling equipment, particularly in still fabrication. This was
        > originally due to its abundance, its malleability using simple hand
        > tools, and its superior heat transfer capabilities over other
        metals.
        > Later, when more modern metals such as stainless steels became
        widely
        > available, it was discovered by accident that these metals
        produced a
        > different and clearly inferior spirit to that produced from the
        same
        > mash employed in copper stills.
        >
        > > >
        >
        > The cause of this anomaly was proven to be stainless steel's inert
        > nature, which allowed the spirit vapour to pass unaltered, whereas
        > copper reacts with any sulphides (rotten egg gases) which are
        always
        > present in grain mashes and removes them from the distillate as
        > sulphates and sulphites. Consequently traditional distillers like
        the
        > Scottish and Irish Whisk(e)y producers rapidly went back to using
        > copper. Today you will see stainless steel used in mash tuns and
        > transfer piping, but in the stills themselves where the ethanolic
        > vapours destined to become potable spirits are separated from the
        water,
        > copper is the fabrication metal.
        >
        > > >
        >
        > > >
        >
        > References
        >
        > 1. Aaseth, J., Norseth, T. (1986). Copper. In: Friberg, L.,
        Nordberg,
        > G.F., Vouk, V.B. Handbook on the toxicology of metals. Second
        edition.
        > Elsevier, Amsterdam, New York, Oxford.
        >
        > 2. Beliles, R.P. (1994). The metals. In: Patty's Industrial Hygiene
        > and Toxicology, Fourth
        >
        > edition, Volume 2, Part C. Edited by Clayton, G.D., and Clayton,
        F.E.
        > John Wiley & Sons, Inc.
        >
        > 3. British Non-Ferrous Metals Federation (1997). Written comments
        on the
        > draft guideline.
        >
        > 4. Codex Alimentarius Commission (1995). Doc. no. CX/FAC 96/17.
        Joint
        > FAO/WHO food standards programme. Codex general standard for
        > contaminants and toxins in foods.
        >
        > 5. Environmental Health Criteria for Copper (1996). PCS/EHC 96.28
        > unedited, page 9.
        >
        > 6. IPCS EHC 200 Copper (1998). Environmental Health Criteria 200.
        World
        > Health
        >
        > Organization, Geneva.
        >
        > 7. JECFA (1982). Evaluation of certain food additives and
        contaminants.
        > Twenty-sixth report of the Joint FAO/WHO Expert Committee on Food
        > Additives. World Health Organization,
        >
        > Technical Report Series 683.
        >
        > 8. Rogers, J., Dowsett, A.B., Dennis, P.J., Lee, J.V., Keevil, C.W.
        > (1994). Influence of plumbing materials on bio film formation and
        growth
        > of Lagionella pneumophila in notable water systems. Appl. Environ.
        > Microbiol. p. 1842-1851.
        >
        > 9. SCF (1993). Reports of the Scientific Committee for Food.
        > Thirty-first series. Nutrient and energy intakes for the European
        > Community.
        >
        > 10. WHO (1998). Guidelines for drinking-water quality. Addendum to
        > Volume 1,
        >
        > Recommendations.
        >
        > 11. Online http://hypertextbook.com/physics/thermal/conduction/ as
        > retrieved on 8 Mar 2006 1:36:26 GMT
        >
        > > >
        >
      • Link D'Antoni
        Harry, Chapter 03 - Metals, is excellent information. Is there a chapter 1 & 2? Or is 1 & 2 akin to Preprepation A through G... I m sure not. I m an
        Message 3 of 5 , Jun 12, 2006
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          Harry,

          Chapter 03 - Metals, is excellent information. Is
          there a chapter 1 & 2? Or is 1 & 2 akin to
          Preprepation A through G... I'm sure not.

          I'm an infomaniac and need a fix.

          Link



          __________________________________________________
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        • Harry
          ... Link, I apologise for that. Yes there s a ch01, 02 and many others. I ve written quite a few papers, diatribes, chapters and notes, essays etc. that
          Message 4 of 5 , Jun 13, 2006
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            --- In Distillers@yahoogroups.com, Link D'Antoni <link2d@...> wrote:
            >
            > Harry,
            >
            > Chapter 03 - Metals, is excellent information. Is
            > there a chapter 1 & 2? Or is 1 & 2 akin to
            > Preprepation A through G... I'm sure not.
            >
            > I'm an infomaniac and need a fix.
            >
            > Link



            Link, I apologise for that. Yes there's a ch01, 02 and many
            others. I've written quite a few papers, diatribes, chapters and
            notes, essays etc. that perhaps one day will be collated into a book
            that others interested in the hobby may find useful. For now, I
            don't really have the time to edit it all. Hopefully one day before
            I die, I'll find the spare time to gather it all together.
            Meantime, all I can suggest is you keep a copy of what's presented
            in these groups, not just by me, but also the other excellent
            offerings from the more experienced members. Who knows? Tomorrow
            we may be hit by a bus. (heh, not likely. Only the good die
            young. ;-) ).


            Slainte!
            regards Harry
          • torch031
            JohnS here again, After reading the this post by Harry about metals I will not be using th heavey Alum pot that I have. Although it can be used, It wont last
            Message 5 of 5 , May 31, 2008
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              JohnS here again,
              After reading the this post by Harry about metals I will not be using
              th heavey Alum pot that I have. Although it can be used, It wont
              last long and there seams to have too many inherent problems attached
              to it for the distilling perposes.

              QUESTION:

              The sheets of copper used for doing copper roofs, are they suitable
              to assist in the construction of a spirit still? My thoughts are to
              use an aluminum coffee urn and line the insides with the copper as I
              am finding it difficult to find a Stainless Steel coffee urn.

              Thanks for any comments in this Idea.

              JohnS


              --- In Distillers@yahoogroups.com, "Harry" <gnikomson2000@...> wrote:
              >
              > As promised, the first draft of the metals paper. It is
              incomplete, and
              > remains a 'work in progress', subject to alteration without notice.
              > However there should be enough info in it to give some food for
              thought,
              > which is what the 'spirit' of this group is about (hopefully). It
              is a
              > long dissertation, so feel free to read, save or discard as you see
              fit.
              > Slainte! regards Harry
              >
              > Chapter 03 - Metals
              > > >
              >
              > From time to time, the subject comes up of `what metals can or
              > can't be used in distilling equipment'. A very simple and safe
              > rule of thumb is this: for contact with alcohol or its feedstock,
              never
              > use any metal that is not used in commercial distilleries for that
              stage
              > of processing. While this may be the easiest approach, it tells you
              > very little about why this or that metal is acceptable or not. Any
              > distiller worth his salt should know exactly why a particular
              material
              > or procedure is employed. Therefore a more complete analysis is in
              > order.
              >
              > > >
              >
              > As a starting point, let's take a look at the metals in commercial
              > distilling plants. Black iron, cast iron, galvanized iron, steel,
              > stainless steel, copper, chromium, aluminium, lead, zinc, nickel,
              brass,
              > various alloys, and several other metals in smaller proportions are
              all
              > found somewhere in a distillery. That does not mean they should
              all be
              > used in the distillation process. On the contrary, most of the
              > aforementioned metals are found in the construction of buildings,
              > peripheral and non-critical machinery. For the distilling process
              > proper, where alcohol and vapours are being manipulated, there are
              only
              > four acceptable metals to use, namely silver, copper, treated
              brass, and
              > stainless steel. The reasons why will become clear as you read
              further.
              >
              > > >
              >
              > Beverage alcohol and the feedstock it is derived from are classed as
              > foods meant for human consumption. Grains, fruits, sugars, ethanol
              > liquid and vapours, and yeasts; all are categorized as foodstuffs.
              > There are very strict rules and regulations governing what
              materials are
              > allowed to come in contact with foods during processing, storage and
              > packaging. These regulations have been formulated after many years
              of
              > rigorous testing of materials and their influence on the foods in
              > question and/or the affects they have on human metabolism. Many
              > countries adopt the policies of International monitoring bodies
              such as
              > the World Health Organization (WHO). This body has published
              > information and recommendations for the materials likely to come
              into
              > contact with foods.
              >
              > > >
              >
              > Like many substances in common usage, the pH of foodstuffs plays an
              > important role in determining which metals are suitable for food
              > contact. Whether a food is acidic, such as tomatoes and soft
              fruits, or
              > neutral or (less common) basic, has a marked influence on the types
              of
              > metals and other materials such as plastics that can be allowed for
              > processing and storage. The temperature of the foodstuff also
              plays a
              > part in determining suitability or otherwise as many foods when hot
              have
              > accelerated reactions in contact with metals. It should be noted
              here
              > that commercial processing and domestic or household usage of
              materials
              > for food contact are two separate situations. In a commercial
              > distillery, everything is subject to regulations regarding
              suitability,
              > safety, and consumer protection and well-being. There are no such
              > safeguards for household usage, save for commonsense and `current
              > practice' methodology. However, as I intimated earlier, a hobby
              > distiller should at least try to follow the practices of commercial
              > processing. Therein lies safety and relative peace of mind.
              >
              > > >
              >
              > The reaction of a metal in contact with foodstuffs is a selection
              > criteria used predominately to avoid metal corrosion and mechanical
              > failure, necessitating costly replacement of equipment. Mashes or
              > `worts' will almost always be acidic, as it is a requirement of
              > yeast to have an acidic environment to perform its functions of
              > producing ethanol and other desirable substances. Mashes fermented
              by
              > yeasts tend to become more acidic as the fermentation progresses.
              Thus
              > the completed wash or `beer' will have a pH of nominally 4.0 or
              > even lower. When fermentation is finished, this acidic beer is now
              > charged to the still and heated. Elementary school chemistry
              teaches
              > that hot acids are extremely corrosive to certain metals, notably
              > aluminium, black iron, certain steels and tin. For this reason
              alone,
              > the aforementioned metals are not really suitable for stillpots,
              boilers
              > or re-boilers, unless of course you like the idea of frequently
              > replacing components of your still. You will note this corrosion
              > resistivity is a separate issue and has nothing to do with possible
              > metal migration into the foodstuff or chemical reactions that may
              form
              > undesirable substances in the wash. That is a selection criterion
              > we'll look at later.
              >
              > > >
              >
              > Regardless of regulations, commonsense tells you that all still
              parts
              > likely to come into contact with hot acidic liquids and vapours
              should
              > be made from a material relatively impervious to corrosion, heat,
              and
              > toxic leaching of chemicals. Copper, food-grade or Austenitic
              stainless
              > steel (304 & 316), and correctly treated brass fill this role
              admirably.
              > I will deal with each in turn, but while we're on the subject of
              > `treated' metals I should make mention of two other metals
              > sometimes considered by the unwary, namely Tin or Tinplate, and
              > Galvanized Iron.
              >
              > > >
              >
              > Easily corroded metals such as Black Iron are often coated with a
              > surface layer of chemicals or other metals to protect the base metal
              > from corrosion. What is not understood by many people is that the
              > composite material is meant to be used in normal everyday use, not
              in
              > harsh chemical processing environments. The galvanizing on the
              surface
              > of the Iron contains Zinc, which is a toxic metal that leaches badly
              > under hot acidic conditions. The Zinc is rapidly eaten away and
              > finishes up in the distillate. The base Iron is then exposed to the
              > acidic wash, resulting in corrosion (rust), which also gets into the
              > processing chain. The stillpot wears out very quickly and needs to
              be
              > replaced frequently. Galvanized Iron has no place in process
              distilling
              > of foodstuffs such as beverage alcohol.
              >
              > > >
              >
              > Similarly, Tin is attacked by both acids and bases (alkali) but has
              the
              > curious property of being relatively stable under neutral pH
              conditions.
              > For this reason, it was commonly used in centuries past as an
              > alternative to copper. However to use Tin, the stillman had to be
              sure
              > the wash was brought to a neutral pH condition, not always an easy
              thing
              > to do given the crude and inaccurate measuring instruments and
              methods
              > (or lack thereof) employed in bygone eras. It is a source of much
              > confusion when the distillers of old tell the young folk "You gotta
              > neutralise the beer". So `young pistol' follows this sage
              > advice and adds Sodium Bicarbonate (a neutralising buffer, pH 8.5)
              to
              > the beer in his brand new copper potstill (tinplate has been largely
              > superseded). Then he gets the fright of his life when the
              distillate
              > runs with a pretty bright blue colour. The blue is, of course, the
              > well-known Cuprous Hydroxide or Schweitzer's Reagent, formed by a
              > complex chemical reaction triggered by the neutral-to-alkaline
              > conditions set up in the Copper still by the S. Bicarbonate. If Tin
              > were the construction material used, there would be no such
              reaction.
              >
              > > >
              >
              > One must always use caution when evaluating procedures from the
              past.
              > Manufacturers from every era strive to refine their processes based
              on
              > the materials and knowledge at hand. However time marches on, and
              > advances in Science & Technology march right along with it.
              >
              > > >
              >
              > > >
              >
              > Corrosion of Metals
              >
              > > >
              >
              > The biggest problem with most metals in distilling, or indeed most
              > processing-type applications, is corrosion. Often it is the
              deciding
              > factor when weighing up the suitability of a metal for a particular
              > duty. It is the driving force behind mankind's quest for newer and
              > more durable metal alloys.
              >
              > > >
              >
              > > >
              >
              > Corrosion occurs when the exposed metal surface reacts
              electrochemically
              > with the surrounding medium in the presence of moisture and oxygen.
              > This reaction results in the formation of surface compounds of the
              metal
              > (e.g. hydroxides). The rate at which corrosion proceeds will
              depend in
              > part on the composition of the aqueous medium. Corrosion of iron in
              > very pure water will be considerably slower than in water containing
              > acids or salts.
              >
              > > >
              >
              > The rate of corrosion depends also on the solubility of the formed
              > compounds in the medium, and their rate of removal. Thus the formed
              > compounds may be removed rapidly in a flowing aqueous medium, and
              the
              > corrosion rate will be high (thinning of the walls of water
              pipes). In
              > a static medium, the rate of corrosion will be moderated as the
              ionic
              > concentration of the surrounding medium increases.
              >
              > > >
              >
              > Corrosion products formed in the atmosphere are more or less
              adherent
              > e.g. rust on iron, verdigris on copper. Rust is essentially
              hydrated
              > ferric oxide which usually also contains some ferrous oxide and may
              > contain iron carbonates and/or sulfates. The equivalent in copper
              is
              > verdigris, consisting mainly of basic copper carbonate, but may also
              > contain copper sulfates and chlorides. However, rust forms loose
              scale
              > and is easily removed, while verdigris forms a stable patina on the
              > Copper surface.
              >
              > > >
              >
              > > >
              >
              > Corrosion resistance
              >
              > > >
              >
              > Some metals (e.g. aluminium, chromium) are rendered "passive" (very
              > resistant to corrosion) by the spontaneous formation, in the
              presence of
              > oxygen, of an invisible and impermeable oxide film a few Angstrom
              units
              > (0.1 nanometers) thick. This passive layer is very strong, very
              adherent
              > and self-repairing if it is damaged. One of the main reasons for
              the
              > production and use of metallic alloys is that alloys are virtually
              > always more resistant to corrosion than are their basic metal
              > components.
              >
              > > >
              >
              > This is partly due to the fact that migration of the constituent
              > elements is much lower than migration from non-alloyed metals,
              because
              > of the micro-structural binding of the elements within the alloys.
              > Stainless steels, which are alloys of iron with a minimum of 10.5%
              > chromium, are orders of magnitude more resistant to corrosion than
              iron
              > itself. This is partly because they possess the general properties
              of
              > alloys, referred to above, but mainly because they have a surface
              > "passive film" which is naturally and rapidly formed on contact
              with the
              > oxygen in air or water. Stainless steels used in food contact
              > applications are invariably used in the passive state.
              >
              > > >
              >
              > So, back to the in-depth analysis of the metals in contact with
              > foodstuffs and how these facts relate to alcohol distillation. For
              this
              > section I draw heavily on the "Guidelines on Metals and Alloys Used
              > as Food Contact Materials", as published by the World Health
              > Organization 09.03.2001. The following metallic materials (and
              others)
              > are covered by these Guidelines: Aluminium, Chromium, Copper, Iron,
              > Lead, Tin, Zinc, Stainless Steel, and other alloys. While not a
              > construction material per se, the following metals are also covered
              > because these elements are present as impurities or contaminants in
              some
              > metallic materials and therefore they can migrate in foodstuffs:
              > Cadmium, Cobalt, and Mercury. At this juncture it must be stressed
              that
              > the release of a substance through migration should be reduced as
              low as
              > is reasonably achievable, not only for health reasons but also to
              > maintain the integrity of the foodstuffs in contact.
              >
              > > >
              >
              > > >
              >
              > Aluminium
              >
              > > >
              >
              > Aluminium Hydroxide, Al(OH)3, is the most stable form of aluminium
              under
              > normally benign conditions. As found in nature it is known as
              > `Gibbsite'. Closely related are `Aluminium Oxide
              > Hydroxide', AlO(OH), and `Aluminium Oxide', Al2O3. They
              > differ only by loss of water from the molecule. These compounds
              > together are the major components of the aluminium ore,
              > `Bauxite'.
              >
              > > >
              >
              > Pure aluminium has good machining properties and high ductility.
              > However its mechanical strength is low. Therefore, aluminium is
              often
              > used combined with other metals as alloys (Beliles, 1994). In
              general
              > usage, aluminium and its alloys are highly resistant to corrosion
              > (Beliles, 1994). When exposed to air, the metal develops a thin
              film of
              > aluminium oxide (AL2O3) almost immediately. The reaction then slows
              > because the film seals off oxygen, preventing further oxidation or
              > chemical reaction. The film is colourless, tough and nonflaking.
              >
              > > >
              >
              > However, aluminium reacts with acids. Most dilute acids attack pure
              > aluminium. At neutral pH, aluminium hydroxide has limited
              solubility,
              > although the solubility increases markedly at pH below 4.5 and
              above 8.5
              > (Elinder and Sjögren, 1986). Alkaline solutions attack both pure
              and
              > impure aluminium rapidly and dissolve the metal (Hughes, 1992).
              >
              > > >
              >
              > > >
              >
              > Aluminium is widely used in food contact materials such as
              saucepans,
              > aluminium -lined cooking utensils, coffee pots, and in packaging
              > products such as food-trays, cans, can ends and closures (Elinder
              and
              > Sjögren, 1986; Codex, 1995). Aluminium food contact materials are
              > often coated with a resin based coating.
              >
              > > >
              >
              > Aluminium alloys for food contact materials may contain alloying
              > elements such as magnesium, silicone, iron, manganese, copper and
              zinc
              > (European Standard EN 601; European Standard EN 602). In aluminium
              cans
              > the production of hydrogen gas from aluminium migration produces an
              over
              > pressure in the can.
              >
              > > >
              >
              > The temperature and storage time is known to influence the
              migration of
              > aluminium into foodstuff. In a migration study with 3% acetic acid
              > (Gramiccioni et al., 1989), the migration was approximately 10 fold
              > higher at 40°C compared to 5°C after 24 hours.
              >
              >
              >
              > In human metabolism, the kidneys excrete aluminium, and only a small
              > amount of aluminium is absorbed (JECFA, 1989). However, soluble
              > aluminium salts are more easily absorbed. Patients with impaired
              renal
              > function treated by dialysis could show a higher aluminium blood
              level.
              > In the past, some of these dialyzed patients have shown neurological
              > symptoms of aluminium intoxication due to an inappropriate
              treatment,
              > which is no longer used. These symptoms have sometimes been
              mistaken
              > for those of Alzheimer's disease. WHO (IPCS 1997) has concluded that
              > aluminium is not the origin of Alzheimer's disease.
              >
              > > >
              >
              > Conclusions
              >
              > Aluminium and its alloys are a poor choice as metals for fabricating
              > distillation equipment. The metal and its normally protective oxide
              > coating formed by atmospheric exposure are subject to severe attack
              and
              > migration in all pH conditions save for neutral pH. As most liquids
              > distilled are normally quite acidic, rapid degradation in the form
              of
              > corrosion and large-scale pitting can be expected. To minimize this
              > situation would require careful neutralization of the wash, which
              has
              > its own inherent problems, particularly if there is any copper
              further
              > along in the distilling path. Alcohol distilled under these
              conditions
              > very often contains undesirable compounds such as the
              > previously-mentioned Schweitzer's Reagent, which will require
              > further processing to eliminate, thus substantially increasing the
              time
              > and cost of distilling.
              >
              > > >
              >
              > If the wash is other than neutral i.e. acidic or alkaline, then
              metal
              > migration will occur into the wash. While the metal and its salts
              may
              > largely remain in the stillpot, undesirable compounds are formed
              which
              > will appear in the distillate and alter the flavour to something
              very
              > different to what was expected. Generally these compounds leave a
              nasty
              > metallic taste on the palate. In wood, this taste gets more
              pronounced
              > as maturation progresses, ruining this batch of spirit. Any
              subsequent
              > batches barreled in that cask will also suffer the same fate, as the
              > undesirable compounds permeate the wood and by virtue of alcohol's
              > known ability as a strong solvent, will leach into any new spirit
              placed
              > therein.
              >
              > > >
              >
              > Rigorous cleaning, perfectly neutral balanced pH wash, meticulous
              > attention to distilling detail, accurate analytical tools e.g. a gas
              > chromatograph, and production of nothing else but flavourless
              neutral
              > ethanol such as vodka, would be the only practical way to employ
              > aluminium successfully in distilling equipment, i.e. a still. Given
              > that there are very few amateur distillers with these skills and
              > instruments, or willingness to be limited to a single product,
              > distillation fabricators would be well advised to discard ideas of
              using
              > aluminium. Utensils and boilers made from aluminium and its alloys
              for
              > grain mashing may fare better, however a minimal maintenance,
              passive
              > metal such as stainless steel would be easily a better option.
              There
              > are eminently more suitable metals than aluminium to employ in
              spirits
              > distilling.
              >
              > > >
              >
              > > >
              >
              > > >
              >
              > > >
              >
              > References
              >
              > 1. ATSDR (1997). Toxicological profile for aluminium. Draft for
              public
              > comment. U.S.
              >
              > Department of Health and Human Services. Public Health Service.
              Agency
              > for Toxic
              >
              > Substances and Disease Registry.
              >
              > 2. Beliles, R.P. (1994). The metals. In: Patty's Industrial Hygiene
              > and Toxicology, Fourth
              >
              > edition, Volume 2, Part C. Edited by Clayton, G.D., and Clayton,
              F.E.
              > John Wiley & Sons, Inc.
              >
              > 3. Codex Alimentarius Commission (1995). Doc. no. CX/FAC 96/17.
              Joint
              > FAO/WHO food standards programme. Codex general standard for
              > contaminants and toxins in foods.
              >
              > 4. Directive 95/2/EC: European Community. European Parliament and
              > Council Directive on food additives other than colours and
              sweeteners.
              >
              > 5. Directive 98/83/EC: Council Directive 98/83/EC of 3 November
              1998 on
              > the quality of
              >
              > water intended for human consumption.
              >
              > 6. Elinder and Sjögren (1986). Aluminium. In: Friberg, L., Nordberg,
              > G.F., Vouk, V.B.:
              >
              > Handbook on the toxicology of metals. Second edition. Elsevier,
              > Amsterdam, New York,
              >
              > Oxford.
              >
              > 7. European Standard CEN EN 601. Aluminium and aluminium alloys -
              > Castings – Chemical composition of castings for use in contact with
              > food.
              >
              > 8. European Standard CEN EN 602. Aluminium and aluminium alloys -
              > Wrought products - Chemical composition of semi products used for
              the
              > fabrication of articles for use in contact with food.
              >
              > 9. Gramiccioni, L. et al. (1989). An experimental study about
              aluminium
              > packaged food. In: "Nutritional and Toxicological aspects of food
              > processing". Proceedings of an international symposium, Rome, April
              > 14-16, 1987. Walker, R. and Quattrucci Eds. Taylor & Francis
              London, p.
              > 331-336.
              >
              > 10.Gramiccioni, L., Ingrao, G., Milana, M.R., Santaroni, P.,
              Tomassi, G.
              > (1996). Aluminium levels in Italian diets and in selected foods from
              > aluminium utensils. Food Additives and Contaminants. Vol. 13(7) p.
              > 767-774.
              >
              > 11.Hughes, J.T. (1992). Aluminium and your health. British Library
              > Cataloguing in Publication Data, Rimes House.
              >
              > 12.IPCS (1997). IPCS report no. 194: Environmental Health Criteria -
              > aluminium. World Health Organization.
              >
              > 13.JECFA (1989). Evaluation of certain food additives and
              contaminants.
              > Thirty-third report of the Joint FAO/WHO Expert Committee on Food
              > Additives. World Health Organization, Technical Report Series 776.
              >
              > 14.Lione, A. (1985). Aluminium toxicology and the aluminium-
              containing
              > medication.
              >
              > Pharmacol. Ther. Vol. 29 p. 225-285.
              >
              > 15.Liukkonen-Lilja, H. and Piepponen (1992). Leaching of aluminium
              from
              > aluminium dishes and packages. Food Additives and Contaminants, vol
              9(3)
              > p. 213-223.
              >
              > 16.MAFF (1998). Lead arsenic and other metals in food. Food
              surveillance
              > paper no. 52. The Stationery Office, London. ISBN 0 11 243041 4.
              >
              > 17.Mei, L., Yao, T. (1993). Aluminium contamination of food from
              using
              > aluminium ware. Intern. J. Environ. Anal. Chem. Vol. 50 p. 1-8.
              >
              > 18.Müller, J.P., Steinegger, A., Schlatter, C. (1993). Contribution
              > of aluminium from packaging materials and cooking utensils to the
              daily
              > aluminium intake. Z. Lebensm. Unters. Forsch. Vol. 197 p. 332-341.
              >
              > 19.Nagy, E., Jobst, K. (1994). Aluminium dissolved from kitchen
              > utensils. Bull. Environ. Contam. Toxicol. Vol. 52 9. 396-399.
              >
              > 20.Pennington, J.A.T., Jones, J.W. (1989). Dietary intake of
              aluminium.
              > Aluminium and Health – A critical review. Gitelman, p. 67-70.
              >
              > 21.Pennington, J.A.T., Schoen, S.A. (1995). Estimates of dietary
              > exposure to aluminium. Food additives and contaminants, vol. 12 no.
              1,
              > p. 119-128.
              >
              > 22.WHO (1993). Guidelines for drinking-water quality. volume 1,
              > Recommendations.
              >
              >
              > Chromium
              >
              > > >
              >
              > Chromium is an essential element to humans. Chroms, knives, spoons
              and
              > forks. Chromium is also used to coat other metals, which are then
              > protected from corrosion because of the passive film which forms on
              the
              > surface of chromiumium is found at low levels in most materials
              used as
              > foods. The main sources of dietary chromium are cereals, meat,
              > vegetables and unrefined sugar, while fish, vegetable oils and
              fruits
              > contain smaller amounts (Codex, 1995).
              >
              > > >
              >
              > Chromium is found in some types of cans and utensils. In cans it
              serves
              > to passivate the tinplate surface. Chromium is used in the
              production
              > of stainless steel of various kinds and in alloys with iron, nickel
              and
              > cobalt. Ferro chromium and chromium metal are the most important
              > classes of chromium used in the alloy industry (Langaard and
              Norseth,
              > 1986).
              >
              > > >
              >
              > Chromium-containing stainless steels (see guideline on stainless
              steel)
              > are important food contact materials used for transportation, e.g.
              in
              > milk trucks, for processing equipment, e.g. in the dairy and
              chocolate
              > industry, in processing of fruit such as apples, grapes, oranges and
              > tomatoes, for containers such as wine tanks, for brew kettles and
              beer
              > kegs, for processing of dry food such as cereals, flour and sugar,
              for
              > utensils such as blenders and bread dough mixers, in slaughter-
              houses,
              > in processing of fish, for nearly all of the equipment in big
              kitchens,
              > such as restaurants, hospitals, electric kettles, cookware and
              kitchen
              > appliances of any kind such as sinks and drains, for bowl.
              >
              > > >
              >
              > Canned foodstuffs in non-lacquered cans and other processed
              foodstuffs,
              > particularly acidic foodstuffs such as fruit juices, may be
              > significantly higher in chromium than fresh foodstuffs. A small
              > contribution to chromium intake can be made by uptake from cans.
              > However, the significance of this is probably negligible. Chromium
              from
              > materials and articles is expected to migrate as Cr(III) and not as
              > Cr(VI) (Guglhofer and Bianchi, 1991). Cr(III) can not migrate at
              > neutral pH in foodstuffs. Therefore, the migration of Cr(III) to
              foods
              > of pH 5 or above is low. Formation of Cr(VI) as a result of a
              > conversion in water of Cr(III) is not possible. Therefore,
              formation of
              > Cr(VI) does not occur in foodstuffs. This implies, that Cr(VI) is
              > generally not considered to be an issue of food contact materials.
              > Also, chromium does not migrate significantly from articles made of
              > stainless steel, and any released chromium is Cr(III) (Cunat, 1997).
              >
              > > >
              >
              > Due to alloying with chromium, the stainless steels resist
              corrosion by
              > foods and are readily cleaned, thereby providing hygiene in food
              > preparation and handling. Chromium is one of the metals which
              naturally
              > forms a corrosion-resistant passive film when in contact with water
              and
              > air (see section on corrosion).
              >
              > > >
              >
              > The specification of chromium is of great importance in
              determining any
              > possible toxicity issues. Cr(III), the most stable oxidation state
              in
              > biological materials, is an essential element for normal glucose
              > metabolism, while Cr(VI) is highly toxic (Beliles, 1994; Costa,
              1997;
              > Nordic Council of Ministers, 1995). Cr(III) has a low toxicity due
              to
              > low absorption (about 0.5%) (Nordic Council of Ministers,1995).
              Toxic
              > aspects of chromium are related to Cr(VI) (Nordic Council of
              Ministers,
              > 1995), due to its high absorption, easy penetration of the cell
              > membranes and its genotoxicity and oxidising properties (Codex,
              1995).
              >
              >
              > Conclusions
              >
              > > >
              >
              > Chromium as a constituent of Stainless Steel manufacture is
              perfectly
              > acceptable as a fabrication material in distilling equipment.
              Likewise,
              > chromium products where the chromium is in direct contact with the
              > distilling fluid path are very safe. As to chromium in foodstuffs
              > through migration, even in harsh acidic conditions below pH 5.0 as
              > commonly found in distilling, it is not considered to be a
              toxicological
              > problem because the recommended human dietary intake is higher than
              > actual values. However chromium tubing and other products as made
              by
              > the electroplating industry for decorative purposes e.g. bath towel
              rods
              > and hand railings is an entirely different matter when applied to
              still
              > fabrication.
              >
              > > >
              >
              > Decorative chrome-plating is a process whereby a thin layer
              (sometimes
              > 50 millionths of an inch) of chromium is applied via chromium salts,
              > acids and electricity, to aesthetically enhance (beautify) the
              > appearance, and/or to prevent tarnishing (staining). It is usually
              > deposited over a thin base layer of nickel or copper previously
              > deposited over the black iron or steel that the tubing is made
              from. To
              > keep costs down the interior of these tubes, not usually seen by the
              > human eye, are prevented from being coated by either the chromium
              or the
              > copper or nickel. Consequently the base tubing metal of black iron
              or
              > steel is exposed to the surrounding environment. Using these tubing
              > products as still components, while they might look pretty, would
              place
              > the exposed iron or steel in direct contact with hot fluids. Thus
              rapid
              > interior oxidation (rusting) of the tubing and/or contamination of
              the
              > ethanol product would result.
              >
              > > >
              >
              > > >
              >
              > > >
              >
              > References
              >
              > > >
              >
              > 1. Beliles, R.P. (1994). The metals. In: Patty's Industrial Hygiene
              > and Toxicology, Fourth
              >
              > edition, Volume 2, Part C. Edited by Clayton, G.D., and Clayton,
              F.E.
              > John Wiley & Sons,
              >
              > Inc.
              >
              > 2. Codex Alimentarius Commission (1995). Doc. no. CX/FAC 96/17.
              Joint
              > FAO/WHO food
              >
              > standards programme. Codex general standard for contaminants and
              toxins
              > in foods.
              >
              > 3. Costa, M. (1997). Toxicity and carcinogenity of Cr(VI) in animal
              > models and humans. Critical Reviews in Toxicology. 27(5) p. 431-442.
              >
              > 4. Cunat, P.-J. (1997). Healthy eating and drinking with stainless
              > steel. 1st SS congress,
              >
              > Thailand, Dec. 1997.
              >
              > 5. Guglhofer, J., Bianchi, V. (1991). Metals and their compounds in
              the
              > environment. VCH
              >
              > Verlag, Weinheim, Germany.
              >
              > 6. Florence, T.M., Batley, G.E. (1980). Chemical speciation in
              natural
              > waters. CRC Critical
              >
              > Reviews in Analytical chemistry. p. 219-296.
              >
              > 7. Langaard, S., Norseth, T. (1986). Chromium. In: Friberg, L.,
              > Nordberg, G.F., Vouk, V.B.
              >
              > Handbook on the toxicology of metals. Second edition. Elsevier,
              > Amsterdam, New York,
              >
              > Oxford.
              >
              > 8. Nordic Council of Ministers (1995). Risk evaluation of essential
              > trace elements - essential
              >
              > versus toxic levels of intake. Report of a Nordic project group.
              Ed.:
              > Oskarsson, A. Nordic
              >
              > Council of Ministers, Copenhagen, Denmark.
              >
              > 9. SCF (1993). Report of the Scientific Committee for food (thirty-
              first
              > series). Nutrient and
              >
              > energy intakes for the European Community.
              >
              > 10. Veien, N.K., Hattel, T., Laurberg, G. (1994). Chromate-allergic
              > patients challenged orally
              >
              > with potassium dichromate. Contact dermatitis. 31 p. 137-139.
              >
              > 11.WHO (1993). Guidelines for drinking-water quality. Volume 1.
              > Recommendations.
              >
              >
              > Copper
              >
              > > >
              >
              > Copper exists in two oxidation states: Cu(I) (cuprous) and Cu(II)
              > (cupric). Copper can also occur in a trivalent state due to certain
              > chemical reactions. Copper is among the most effective of metal
              > biochemical oxidising agents. Copper is an essential element to man
              > (Aaseth and Norseth, 1986). Copper also has the ability to restrict
              > bacterial growth, e.g. Legionella, in drinking water systems
              (Rogers et
              > al., 1994).
              >
              > > >
              >
              > Copper is naturally present in most foodstuffs in the form of copper
              > ions or copper salts (Codex, 1995). The main sources are meat,
              offal,
              > fish, pecans, milk chocolate and green vegetables (Aaseth and
              Norseth,
              > 1986).
              >
              > > >
              >
              > Copper vessels are traditionally used in many specialised food
              > processing activities, such as breweries and distilleries, for
              > cheese-making, chocolate, dry vegetables, jam and sweets
              production. In
              > food utensils, copper is in general used unalloyed, for exam ple in
              > saucepans, which are usually lined inside with tin or stainless
              steel.
              > Copper is used in alloys, particularly brass, bronze, and nickel
              silver
              > (British Non-Ferrous Metals Federation, 1997).
              >
              > > >
              >
              > Copper is slowly attacked by dilute hydrochloric acid or dilute
              sulfuric
              > acid and is soluble in ammonia water (Beliles, 1994). Acidic
              foodstuffs
              > can attack copper in utensils. Therefore, copper may be present in
              > foodstuffs due to migration from food contact materials, e.g. copper
              > utensils, copper pipes, etc. (Codex, 1995) or from using drinking
              water
              > from copper pipes for food preparation. In some cases, high copper
              > migration might induce some discoloration. Migration from copper
              into
              > sugar confectionery cooked at 125-140 °C and at pH 5.1-6.0 on
              average
              > increases the copper concentration in the confectionery from 0.13
              mg/kg
              > to 0.25 mg/kg (Written comments from BCCCA, 1999).
              >
              > > >
              >
              > Copper is one of the best conductors of heat available. Only
              silver has
              > a higher thermal conductivity, while stainless steel is a relatively
              > mediocre conductor. (Hypertextbook Physics, 2006).
              >
              > > >
              >
              > > >
              >
              > Conclusions
              >
              > > >
              >
              > The level of contamination of copper observed in drinking water and
              > foodstuffs does not constitute a safety problem. There is a greater
              > risk of adverse health effects from copper deficiency, than from
              > excessive copper intake.
              >
              > > >
              >
              > Copper has been employed for centuries as the metal of choice in
              > distilling equipment, particularly in still fabrication. This was
              > originally due to its abundance, its malleability using simple hand
              > tools, and its superior heat transfer capabilities over other
              metals.
              > Later, when more modern metals such as stainless steels became
              widely
              > available, it was discovered by accident that these metals produced
              a
              > different and clearly inferior spirit to that produced from the same
              > mash employed in copper stills.
              >
              > > >
              >
              > The cause of this anomaly was proven to be stainless steel's inert
              > nature, which allowed the spirit vapour to pass unaltered, whereas
              > copper reacts with any sulphides (rotten egg gases) which are always
              > present in grain mashes and removes them from the distillate as
              > sulphates and sulphites. Consequently traditional distillers like
              the
              > Scottish and Irish Whisk(e)y producers rapidly went back to using
              > copper. Today you will see stainless steel used in mash tuns and
              > transfer piping, but in the stills themselves where the ethanolic
              > vapours destined to become potable spirits are separated from the
              water,
              > copper is the fabrication metal.
              >
              > > >
              >
              > > >
              >
              > References
              >
              > 1. Aaseth, J., Norseth, T. (1986). Copper. In: Friberg, L.,
              Nordberg,
              > G.F., Vouk, V.B. Handbook on the toxicology of metals. Second
              edition.
              > Elsevier, Amsterdam, New York, Oxford.
              >
              > 2. Beliles, R.P. (1994). The metals. In: Patty's Industrial Hygiene
              > and Toxicology, Fourth
              >
              > edition, Volume 2, Part C. Edited by Clayton, G.D., and Clayton,
              F.E.
              > John Wiley & Sons, Inc.
              >
              > 3. British Non-Ferrous Metals Federation (1997). Written comments
              on the
              > draft guideline.
              >
              > 4. Codex Alimentarius Commission (1995). Doc. no. CX/FAC 96/17.
              Joint
              > FAO/WHO food standards programme. Codex general standard for
              > contaminants and toxins in foods.
              >
              > 5. Environmental Health Criteria for Copper (1996). PCS/EHC 96.28
              > unedited, page 9.
              >
              > 6. IPCS EHC 200 Copper (1998). Environmental Health Criteria 200.
              World
              > Health
              >
              > Organization, Geneva.
              >
              > 7. JECFA (1982). Evaluation of certain food additives and
              contaminants.
              > Twenty-sixth report of the Joint FAO/WHO Expert Committee on Food
              > Additives. World Health Organization,
              >
              > Technical Report Series 683.
              >
              > 8. Rogers, J., Dowsett, A.B., Dennis, P.J., Lee, J.V., Keevil, C.W.
              > (1994). Influence of plumbing materials on bio film formation and
              growth
              > of Lagionella pneumophila in notable water systems. Appl. Environ.
              > Microbiol. p. 1842-1851.
              >
              > 9. SCF (1993). Reports of the Scientific Committee for Food.
              > Thirty-first series. Nutrient and energy intakes for the European
              > Community.
              >
              > 10. WHO (1998). Guidelines for drinking-water quality. Addendum to
              > Volume 1,
              >
              > Recommendations.
              >
              > 11. Online http://hypertextbook.com/physics/thermal/conduction/ as
              > retrieved on 8 Mar 2006 1:36:26 GMT
              >
              > > >
              >
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