Food Chemistry

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 generaCandida(Mycoderma),Pischiaand
Hansenula(Willia). Other microorganisms are in-
volved 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 de-
tectable. It has usually been associated with man-
nitol fermentation which may result in consider-
able amounts of mannitol.
Sorbic acid can be converted to 2-ethoxy-3,5-
hexadiene by heterofermentative lactic acid bac-
teria. 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 microor-
ganisms 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 over-
saturation, 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 alco-

hol content is at least 15% by volume and at most

22% by volume. The production proceeds accord-

ing to two different processes, which are partly

also combined:

• Concentrated liqueur winesare 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 pres-

ence 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 matura-

tion. 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 for-

tified with wine distillates. The fortifying proce-

dure is repeated several times (“multiple addit-

ion”) 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 con-

centration 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 im-

parts 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).