2009_Book_FoodChemistry

916 20 Alcoholic Beverages
the instable aglycones during fermentation. Of
special analytical interest are the anthocyan glucosides
which are not attacked by the hydrolases
and can easily be separated by RP-HPLC. These
glucosides occur as side products and are acylated
with acetic acid, p-cumaric acid or caffeic
acid. The spectrum of the pigments depends
on the grape cultivar, e. g., Cabernet Sauvignon
contains about three times as much malvidin-3-
acetylglucoside as malvidin-3-cumarylglucoside.
However, the acylated anthocyans also decrease
with time due to oxidation and condensation
reactions. Consequently, their detection in wines
that are more than 2–3 years old becomes
increasingly difficult.
Cyanidin-3-glucoside is a suitable indicator of
cherry wines which have been added to a wine
to intensify the red color.
20.2.3.3.6 Minerals
Must contains predominantly potassium, followed
by calcium, magnesium, sodium and iron.
Important anions are phosphate, sulfate, silicate
and chloride.
20.2.3.3.7 Aroma Substances
The must aroma substances will be discussed together
with wine aroma substances (cf. 20.2.6.9).
20.2.4 Fermentation
Wine fermentation may occur spontaneously due
to the presence of various desirable wine yeasts
and wild yeasts found on the surface of grapes.
Fermentation can also be conducted after must
pasteurization by inoculation of the must with
a pure culture of a selected strain of wine yeast.
Wild yeasts include Saccharomyces apiculatus
and exiguus, while the pure selected yeasts are
derived from Saccharomyces cerevisiae var. ellipsoides
or pastorianus. The pure wine yeast possesses
various desirable fermentation properties.
High fermenting strains are used to give high alcohol
wines (up to 145 g/l) and those which are
resistant to tannin and high alcohol levels are used
in red wine fermentation. Other types of yeast are
“sulfite yeast” with little sensitivity to sulfurous
acid (sulfur dioxide solutions), “cold fermentation
yeasts”, which are active at low temperatures
and, finally, special yeasts for sparkling wines,
which are able to form a dense, coarse-grained
cloudiness that is readily removed from the wine.
The desired yeasts (5–10 g of dried yeast per hectoliter
of must) are added to must held in fermenters
(vats made of oak, or chromiumnickel
steel tanks lined with glass, enamel or plastic).
The must is then fermented slowly for up to 21
days below 20 ◦ C for white wines or 20–24 ◦ C
for red wines. The course of fermentation is influenced
by sulfurous acid: 100 mg/l SO 2 delay
the start of fermentation by 3 days, 200 mg/lSO 2
by 3 weeks.
As a safeguard against air (discoloration), bacterial
spoilage (acetic acid bacteria) and also to
retain carbon dioxide, the liquid loss in the fermenter
is compensated for by topping up with the
same wine. After the end of main (primary) fermentation,
which lasts 5–7 days, the sugar has
been largely converted to alcohol while the protein,
pectin and tannins, along with tartrate and
cell debris, settle with the yeast cells at the bottom
of the fermenter. This sediment is called bottom
mud, dregs or lees.
Partial precipitation of tartaric acid as cream of
tartar (mixture of K hydrogentartrate and Ca tartrate)
is affected by temperature, alcohol content
and pH (Fig. 20.6). The crystallization of tartar
can be retarded by the addition of metatartaric
acid (up to 100 m/l), obtained by heating tartaric
acid above the melting point. The addition is carried
out directly before bottling. A tartar stability
of 6–9 months is achieved. After this period,
the metatartaric acid is slowly converted to tartaric
acid. The unfermented residual sugar (residual
sweetness) may be retained when necessary, if
the secondary fermentation is suppressed by addition
of sulfurous acid. Fermentation stops at an
ethanol concentration of 12–15% (v/v), depending
on the type of yeast.
The young wine, which is drunk with the yeast in
some regions of Germany and Austria (“Federweisser”
or “Sauser”), is usually withdrawn from
the fermentation tank via clarifying separators
after the primary fermentation. Red wine mash
is fermented at somewhat higher temperatures
by using various procedures, often in closed