2009_Book_FoodChemistry

926 20 Alcoholic Beverages
centrations of 15–20 ng/l, it contributes to the
cork flavor of wine. Geosmin, 1-octen-3-one, 4,5-
di-chloroguaiacol and chlorovanillin may cause
musty off-flavors.
Additional yeast spoilage is induced by species
of the genera Candida (Mycoderma), Pischia and
Hansenula (Willia). Other microorganisms are involved
in the formation of viscous, moldy and
ropy wine flavor defects. Bacterial spoilage may
involve acetic acid and lactic acid bacteria. In
this case vinegar or lactic acid souring is detectable.
It has usually been associated with mannitol
fermentation which may result in considerable
amounts of mannitol.
Sorbic acid can be converted to 2-ethoxy-3,5-
hexadiene by heterofermentative lactic acid bacteria.
In concentrations of 0.1m/l, this compound
produces a “geranium” note.
A “mousy” taint is occasionally detected in fruit
and berry wines and, less often, in grape wines.
It is thought that the tetrahydropyridines given
in Table 20.24, which have been also identified
as important flavor compounds of toasted bread
(cf. 15.4.3.3.2), contribute to the “mousy” taint.
These compounds might be formed by microorganisms
in wine.
Likewise, red wines, particularly color-deficient
wines, show a microbiologically-induced change
reflected in a substantial increase in volatile
acids and the degradation of tartaric acid and
glycerol. The bitter taste of red wines is caused
by bacteria, mold and yeast. The bitter taste is
usually a result of glycerol conversion to divinyl
glycol. Cloudiness of red wines appears to be
due either to bacterial or yeast spoilage or to
physical reasons alone, such as the precipitation
of cream of tartar. The latter occurs frequently
and mostly in bottled wines. Cream of tartar
precipitates as a result of oversaturation of the
salt solution, as appears to be the case with
protein-tannin interaction products. With oversaturation,
they sediment as a fine greyish-yellow
haze. Cloudiness caused by mucic acid salts also
occurs.
20.2.8 Liqueur Wines
In contrast to wine, liqueur wines (older term
“dessert wines”) are not exclusively made from
fresh or mashed grapes or grape must. The alcohol
content is at least 15% by volume and at most
22% by volume. The production proceeds according
to two different processes, which are partly
also combined:
• Concentrated liqueur wines are produced by
the fermentation of concentrated grape juices
which are very rich in sugar (e. g., from dry
grapes) or by the addition of concentrated
grape juice to wine.
• Mixed liqueur wines (e. g., Sherry/Malaga,
Port wine/Madeira, Samos, Marsala) are
produced from partly fermented must with
the addition of alcohol or mixed thickened
must. The addition of alcohol stops the
fermentation.
The extract, alcohol and sugar contents of dessert
wines are given in Table 20.25.
At least 2–5 years are needed to make dessert
wines. In the production of sherry the wine is
stored in partially filled butts, i. e. in the presence
of excess air. Flor yeasts develop on the wine
surface in the form of a continuous film or wine
cover (sherry yeast). The typical sherry flavor is
derived from the aerobic conditions of maturation.
During this time the concentrations of the
following compounds increase at the expense of
alcohol and volatile acids: ethanal, acetals, esters,
sotolon (cf. 5.3.1.3) and 2,3-butylene glycol. In
port wine production the wine is drawn off to
casks before the end of fermentation and is fortified
with wine distillates. The fortifying procedure
is repeated several times (“multiple addition”)
until the desired alcohol content is reached.
Sotolon is the key aroma substance of Port wine.
Its odor threshold in this wine is 19 µg/l. Its concentration
increases linearly during storage. Port
stored for one year and for 60 years contained 5
and 958 µg/l sotolon respectively.
20.2.9 Sparkling Wine
Experience has shown that carbon dioxide imparts
a refreshing, prickling and lively character
to wine (as already mentioned for young wines).
Hence, the production of a refined form of wine,
enriched with carbon dioxide (sparkling wine)
was developed and used in the early 18th Century,
originally in the Champagne region of France
(“Champagne” wine).