Whisky Raw Materials: Barley and Green Malt
Although it can be relatively inexpensive compared to maize and wheat,
unmalted barley has been rarely used in grain distilleries because of the processing problems associated with high levels of gums such as b-glucans(Walker, 1986).
In grain distilleries barley is generally used in the form of malt, and its
primary function is as a source of enzymes to convert cereal starch from
unmalted cereals such as wheat or maize into fermentable sugars.
According to the legal definition of Scotch whisky, all of the enzymes in a
mash must come from the malt, and no other externally added enzymes are permitted.
It is essential that barley malt for grain distilling, which is often described as
high diastase malt, contains high levels of starch-degrading enzymes. Enzyme levels in barley malt are normally defined in terms of dextrinizing units (DU),
which is effectively a measure of a-amylase and diastatic power (DP). DP is
essentially the total enzyme (a- and b-amylase) activity, as measured using
standard methodology (Institute of Brewing, 1997). Barley for grain distilling must contain high levels of b-amylase and have the potential to produce high levels of a-amylase, limit-dextrinase and a-glucosidase.
Generally barley malt with a DP of 180200 units and a DU above 50
units is considered to be the standard requirement for grain distilling malt
(Bathgate, 1989). Since barley malt is a relatively expensive component of the
production cost in grain distilleries there is a continuing drive to reduce costs
by limiting the amount of malt used, and this has resulted in malt inclusion
rates falling to less than 10 per cent in some cases. The main effect of this is
that it is now more important than ever for grain distilling malt to meet high
The process of preparing malted barley for distilling is covered in detail in
Chapter 2. However, there are some differences both in the process used and
in the type of barley that is suitable for malting. The main features of the
process of malting grain distilling barley are that the barley is allowed to
germinate for a longer period, typically five to six days, and that a gentler
kilning regime (50608C) is used (if at all) in order to develop and preserve
enzyme activity. The use of green malt preserves around 3550 per cent of the
enzyme activity that would otherwise be lost on kilning (Bathgate, 1989).
Barley for grain distilling generally has a higher nitrogen content (1.82.0
per cent) than that for pot still (malt distilling) barley (Bathgate and Cook,
1989). This is because grain distillers are less interested in the amount of
starch that is present (although this does contribute a small but significant
proportion of alcohol yield) than in developing the highest possible enzyme
Originally, unkilned green malt was largely used for grain distilling, and
malting was generally carried out at the distillery using local or domestic
barley. Green malt was generally cheaper to produce, due to lower energy
costs, and gave higher enzyme levels than kilned malt, so that a lower dosage
rate was required to achieve efficient of conversion of starch. However, these
advantages were offset by higher transport costs and a shorter shelf life
The use of green malt has gradually declined in favour of commercially
produced kilned malt, although some grain distilleries still continue to use
green malt. However, in mid-2002 the last on-site production facility was
replaced by commercially produced green malt (Robson, 2002).
[Source: Whisky: Technology, Production and Marketing 2003