energy reserves it contains for the growing barley plant. To encouraged
this, maltsters sometimes add gibberellins, plant growth hormones which
are the natural regulators of this process.
The development from a seed to a plant is arrested by kilning which
reduces the moisture content of the malt to 3–5%. During kilning, some
non-enzymic browning reactions occur between amino acids and sugars
in the malt and these contribute to the final beer colour. Darker beers
tend to include malts that have been kilned at higher temperatures to
promote browning reactions.
Nowadays malts are usually bought in by brewers as one of their raw
materials and the brewing process proper starts with its conversion into a
liquid medium (wort) capable of supporting yeast growth: a step known
as mashing (Figure 9.11).
The malt is ground to reduce the particle size and increase the rate of
enzymic digestion and is then mixed with hot water. Water, known in
brewers’ parlance as liquor, is an important ingredient in brewing and
the quality of the local water was one of the reasons for the development
of traditional UK brewing centres such as Burton on Trent, London and
Edinburgh. In particular, calcium content has a significant impact on the
brewing process because calcium ions precipitate out as calcium phos-
phate during mashing. This decreases the wort pH from 6.0 to 5.4, nearer
the optimum for a number of malt enzymes, and thus increases the yield
of fermentable extract. Starchy adjuncts may be added during mashing
to boost the fermentable sugar content of the wort.
There are two traditional systems of mashing: the British technique of
infusion mashing where the mash is held in a single vessel at a constant
temperature of around 65 1 C, and the continental decoction system
where the mash is heated through a range of temperatures by removing
a portion, heating it, then adding it back. Nowadays a number of
variations on these techniques are used so that the differences are less
distinct.
In mashing, a number of enzymic activities contribute to the produc-
tion of the clear liquid medium known as sweet wort. For instance, it
requires two enzymes operating in concert to break down starch into
maltose, a disaccharide of glucose fermentable by the brewing yeast.
Barley starch is composed of two fractions: amylose (20–25%), a linear
polymer of a-1,4-linked glucose units, and amylopectin (75–80%), a
branched polymer containing linear chains ofa-1,4-linked glucose units
with branches introduced by occasionala-1,6-linkages. Alpha amylase
hydrolyses a-1,4-linkages to produce a mixture of lower molecular
weight dextrins while the exoenzyme,b-amylase, attacks dextrins at their
non-reducing end, snipping off maltose units. Limit dextrins containing
thea-1,6-linkages are left in the wort largely untouched unless the non-
malt enzyme amyloglucosidase is added to the mash.
350 Fermented and Microbial Foods