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Re: Yeast Propagation in a Whisky Distillery

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  • Harry
    Further Info: Saccharomyces spp. and other fermentative yeasts cannot grow indefinitely under anaerobic conditions without certain nutrient supplements that
    Message 1 of 2 , May 1, 2008

      Further Info:

      Saccharomyces spp. and other fermentative yeasts cannot grow

      indefinitely under anaerobic conditions without certain nutrient supplements

      that are unnecessary aerobically. Sterols and unsaturated fatty acids, the

      essential cell membrane components of yeasts (and indeed of all eukaryotic

      organisms), cannot be synthesized anaerobically, thus limiting anaerobic

      yeast growth to two or three generations unless these compounds are provided

      in the culture medium. Secondly, fermentative yeasts are not true

      facultative anaerobes, since the Crabtree effect (Fiechter

      et al., 1981; Young,

      1996) takes precedence. Above about 1 per cent fermentable sugar in the

      culture medium (the exact percentage varying between strains) the yeast

      ferments the sugar by anaerobic metabolism, no matter how well the culture

      medium may be aerated. Instead, the dissolved oxygen is used for the

      biosynthesis of membrane fatty acids and sterols, thereby permitting more

      extensive growth when aerobic conditions are no longer available. Therefore,

      although deliberate addition of unsaturated fatty acids and sterols to wort

      to encourage yeast growth is certainly not permitted for Scotch whisky

      fermentations, the same effect can be achieved legally by aeration of the

      wort.

      In a paper partly reporting their own experience but also extensively

      reviewing the literature on the Pasteur and Crabtree effects, O'Connor-

      Cox

      et al. (1996) stated that of the dissolved oxygen present in the wort

      at the start of the brewery fermentations, only about 30 per cent was used

      directly for synthesis of unsaturated fatty acids and sterols. It has been

      well established that none is used for the oxidative metabolism of sugars

      (see, for example, Lagunas, 1986).


       [Source: Whisky

      Technology, Production and Marketing
       
      Elsevier, 2003

      Edited by: Inge Russell, Graham Stewart, Charlie Bamforth and Inge
      Russell
       
      ISBN: 978-0-12-669202-0]

      HTH

      Slainte!
      regards Harry

      >

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