2009_Book_FoodChemistry

900 20 Alcoholic Beverages
enzyme inactivation. On the other hand, when
a low alcohol beer is desired, the malt mashed
at 37 ◦ C is drained into boiling water, increasing
the temperature to 70 ◦ C and resulting in extensive
enzyme inactivation.
In infusion mashing, used mostly in England for
brewing top fermented beer, the terminal mashing
temperature is achieved not by stepwise increases,
but by live steam injection or addition of
hot water. As in the decoction method, the temperature
program used can vary greatly.
Wort boiling with hops or hop products is done
in a brew kettle (hop kettle) in which the initial
and subsequent worts from the lautering step are
collected. Addition of hops is adjusted according
to the type and quality of beer desired. The quantity
(in hop cones/hectoliter) for light lager beer is
130–150 g; for Dortmund-type beer, 180–220 g;
for Pilsener beer, 250–400 g; for dark Munich
beer, 130–170 g; and for malt beer and dark bock
beer, 50–90 g. The critical factor is the content of
bitter substances in the hops selected. The utilization
of the bitter substances (α-acids) is only 30–
35%.
Boiling for 70 to 120 min concentrates the wort,
coagulates protein (“break forming”), solubilizes
hop ingredients and converts the bitter components
to their isoforms and, lastly, inactivates enzymes.
The hot wort is then chilled, filtered, aerated
and, finally, “pitched” with yeast.
In modern processes, the classical brew kettle
is replaced by a whirlpool kettle with external
cooker. Shorter boiling times and a better quality
of beer are achieved with this system. Moreover,
separation from the spent hops can be conducted
in the same vessel.
Processes that use pressure boiling (hightemperature
wort boiling up to 150 ◦ C) can
produce beer with an unpleasant cooked taste.
20.1.4.3 Lautering
The separation of wort from hulls and insoluble
residues of the grain is done by a classical procedure
in a lauter tun, a vessel with a slotted false
bottom. The hull and other residues form a ca.
35 cm deep layer in the bottom which acts as a filter
through which the extract, or wort, is strained.
The initial turbid liquid (turbid wort) with 16–
20% extract is pumped back to the tun. Finally,
to obtain more wort, the spent grains are rinsed or
sparged 3 to 4 times with water.
Modern installations for lautering use strain masters
or discontinuous or continuous mash filters.
The draff, the lautering residue, is used for animal
feed.
20.1.4.4 Wort Boiling and Hopping
20.1.4.5 Continuous Processes
Efforts are being made to introduce continuous
processes via heat exchangers and to save energy
and make the process environmentally friendly
with heat recovery from the exhaust steam.
Wort treatment, i. e., removal of the trub formed
during boiling (protein-polyphenol complexes,
cf. 18.1.2.5.8), is generally conducted in whirlpool
vats (possibly combined with wort drying)
or via continuous centrifuges. After cooling
to the pitching temperature (6–8 ◦ C), the cooling
trub obtained is separated by filtration or
centrifugation.
20.1.5 Fermentation
20.1.5.1 Bottom Fermentation
Bottom fermentation involves a primary and
a secondary step. In the primary fermentation
step, the cooled wort with about 6.5–18%
dry mass extracted from malt (“stemwort”) is
pumped into fermenting tanks, located in fermentation
cellars cooled to 5–6 ◦ C. The tanks
are made of plastic-lined concrete, enamelcoated
steel, aluminum or V 2 A steel. The wort is
inoculated (“pitched”) with yeast in the form
of a thick yeast slurry of Saccharomyces Carlsbergensis
(0.5–1 l/hl) and fermented at 8–14 ◦ C
until more than 90% of the fermentable extract
has been converted. The primary fermentation
is completed in 7–8 days, at which point the
yeast “breaks”, i. e., flocculates and settles to the
bottom. The beer is transferred to large clean