Food Chemistry

914 20 Alcoholic Beverages

Fig. 20.5.Sylvaner wine grape ripening with measure-
ment of the content of acid (as tartaric), sugar (as glu-
cose), 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

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 fer-

mented to provide pomace wine. This is con-

sumed as a homemade drink and is not mar-

keted. 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 dis-

coloration and the growth of undesirable microor-

ganisms. In order to remove undesirable odors or

off-tastes, the must is treated with activated char-

coal and, when necessary, is clarified by sepa-

rators or filters. In general, sulfurization before

fermentation is dispensed with if the material is

faultless and pure culture yeast is used. If re-

quired, 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

Table 20.13 provides data on the average compo-

sition of grape musts. For the quality assessment

of grape must, its relative density at 20◦Cisde-

cisive. 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 )× 103 (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