2009_Book_FoodChemistry

898 20 Alcoholic Beverages
harvested for use in freshly-prepared worts, until
the yeast becomes useless due to contamination
or degeneration. In this way, it is possible to
continuously select suitable yeast strains for
a defined goal.
20.1.3 Malt Preparation
The cereals are soaked (steeped) in water and then
allowed to germinate. The product, green malt, is
dried and mildly roasted into a more or less dark
and aroma-rich kiln-dried malt. During processing,
the rootlets are removed from the malt. The
loss due to malting is 11–13% of the dry weight.
Prior to use, the malt is stored for 4–6 weeks.
20.1.3.1 Steeping
Cereal kernels are steeped in water to raise
their moisture content to induce germination.
The water content is 42–44% for light and
44–46% for dark malt. Usually the steeping
water is alternately added and removed. Barley
is first steeped for only 4–6 h at 12–15 ◦ C water
temperature so that the water content is adjusted
to ca. 30%. In the following dry period, which
lasts 18–20 h, the grains swell and enzymatic
processes start rapidly. In the second wet steeping
at ca. 18 ◦ C, a water content of 38% is obtained
in 2 h. Good aeration is needed in all phases
to remove the CO 2 produced by respiration.
The normal steeping temperature is 12–24 ◦ C.
Alkali treatment (CaO, NaOH) of steeping water
serves to reduce microbial contamination and
to remove undesirable polyphenols from the
hulls.
20.1.3.2 Germination
When the cereals reach the desired moisture
content (after ca. 26 h) and germination is started,
they are allowed to germinate in germinator
chests or less often in drums. The removal of
CO 2 and heat is achieved by blowing in moist
air (500 m 3 /t). The sprouts appear at 16–18 ◦ C
in 16–20 h. The water content of barley is first
increased to ca. 41% by spraying and then in
steps to 47% to further support germination. The
growth of the rootlet continues up to 1.5 times
the grain length. At the end of the process which
on the whole lasts ca. 40–50 h, the temperature is
reduced to 11–13 ◦ C. The law in some countries
allows the addition of growth substances to
accelerate germination, e. g., gibberellic acid.
20.1.3.3 Kilning
The germinated cereals, termed green malt, contain
43–47% moisture. They are dried in a kiln
to give a storable malt with a water content from
2.5% (dark) to 4.5% (lager).
Light malt requires fast drying so that the Maillard
reaction does not get a look-in. The process
is carried out in high-performance kilns at
a temperature which is raised from 50 to 65 ◦ C.
The barley heats up and germination stops above
40 ◦ C at a water content which is reduced to 20%.
However, the activities of hydrolases (endopeptidases,
α-amylases) still increase, as desired. The
final drying is carried out at 82–85 ◦ C, leading to
unavoidable enzyme losses.
In the production of dark malt, the moisture is
withdrawn so slowly that the material temperature
is higher than with light malt. Although this
results in an inhibition of germination, there is
an extension of the period in which the activities
of the hydrolases increase. The degradation
of proteins and carbohydrates to precursors of
the Maillard reaction is correspondingly extensive.
Finally, the malt is rapidly dried at 100 to
105 ◦ C, the Maillard reaction providing intensive
color and aroma substances.
20.1.3.4 Continuous Processes
Several kinds of installations have been developed
which provide continuous steeping,
germination and, occasionally, also kilning,
offering substantial savings in time. Steeping
in this case is performed as a single washing
followed by water spraying and continuous
transferring to the germination stage. The process
conditions are regulated by means of forced
air. In some installations the malt is moved for