2009_Book_FoodChemistry

914 20 Alcoholic Beverages
to 50 ◦ C prior to fermentation of the mash, or to
30 ◦ C after the main fermentation, followed by
a short additional fermentation.
The left over stems, skins and seeds provide the
pomace. It is used as feed or fertilizer, or is fermented
to provide pomace wine. This is consumed
as a homemade drink and is not marketed.
Pomace brandy is obtained by distillation
of fermented pomace. The average must yield
is 75 l/100kg grapes. Of this, 60% is free juice
(must), 30% press-must and 10% must from the
second pressing.
The fresh, sweet must can be treated with sulfur
dioxide (50 mg SO 2 /l) to suppress oxidative discoloration
and the growth of undesirable microorganisms.
In order to remove undesirable odors or
off-tastes, the must is treated with activated charcoal
and, when necessary, is clarified by separators
or filters. In general, sulfurization before
fermentation is dispensed with if the material is
faultless and pure culture yeast is used. If required,
the must is pasteurized by a short heat
treatment (87 ◦ C/2min).
The addition of sugar to and deacidification of
must will be discussed in 20.2.5.4.
20.2.3.3 Must Composition
Fig. 20.5. Sylvaner wine grape ripening with measurement
of the content of acid (as tartaric), sugar (as glucose),
weight of 1000 berries and water content of the
berries
is produced. The remaining grape skins and seeds
(pomace) are loosened or shaken-up and pressed
again. This provides the second or post-extract.
In red wine making the crushed berries (the
mash) are fermented without prior removal of
the pomace, i. e. the must is fermented together
with the skin. This is done in order to extract
the red pigments localized in the skin, which
are released only during fermentation. When
blue grapes are processed in the same manner as
white ones, or blends of blue and white grapes
are combined and then processed, pink wines are
obtained. They are designated as rosé wines. In
red wine making the extraction of red pigments is
sometimes facilitated by raising the temperature
Table 20.13 provides data on the average composition
of grape musts. For the quality assessment
of grape must, its relative density at 20 ◦ Cisdecisive.
This is measured with a special aerometer
(must balance). The must weight M, expressed in
Oechsle degrees, is directly read off.
M [ ◦ Oe]=(D − 1) × 10 3 (20.6)
Accordingly, a must with D = 1.080, has an M
of 80 ◦ Oe. In Germany, the quality levels for
Table 20.13. Average composition of grape must
Constituent
Content
(g/l)
Water 780–850
Sugar (as glucose) 120–250
Acids (as tartaric acid) 6–14
N-Compounds 0.5–1
Minerals 2.5–3.5