Food Chemistry

918 20 Alcoholic Beverages

stability and hence for the quality of the wine. Ef-
forts are made to achieve 30–50 mg of free SO 2 /l
of finished wine.

20.2.5.3 Clarification and Stabilization

Suitable measures should not only eliminate any
turbidity present, but also prevent its formation
during storage (fining).
Turbidity-causing solids are mostly proteins as
well as oxidized and condensed polyphenols. Fur-
thermore, multivalent metal ions can cause dis-
coloration and sediments. Wine clarification is
usually achieved by precipitation reactions, fil-
tration or centrifugation. In blue-fining the ex-
cess metal ions which are responsible for metal-
induced cloudiness (iron, copper and zinc) are
precipitated by precisely calculated amounts of
potassium ferrocyanide. In this process, soluble
Berlin blue is formed first,

KFe(CN) 6 +FePO 4 →KFe 4 ·

Fe(CN) 6 +K 3 PO 4

(20.8)

which is then converted to insoluble Berlin blue.

3KFe 4 (CN) 6 +3FePO 4 →Fe 4 ·

Fe(CN) 6 +K 3 PO 4

(20.9)

The blue turbidity formed helps to eliminate the
persistent protein turbidity (grayish and black
casse). The treated wine is tested for excess
cyanoferrate and for free cyanide to be on the
safe side. In other fining procedures, edible
gelatin, isinglass (beluga dried bladder gelatin)
combined with casein, egg albumen, tannin, iron-
free bentonite, kaoline, agar-agar and purified or
activated charcoals are added to the wine. This
results in adsorption or precipitation of the sub-
stances causing cloudiness and unpleasant taste,

the interaction products all being quick-settling
coagulums. Phenolic compounds are removed
from wine by polyvinylpyrrolidone (detanniniz-
ing) and undesirable sulfur compounds by cupric
sulfate.
The clarification by filtering involves pads of as-
bestos, cellulose, infusorial earth, and filter aids
such as Hyflo Super Cel and Filter Cel. The fil-

ters are built either as sheet filters or as washable

filter presses. Sterile filtration has achieved great

importance for the stability of wine and sweet

must. Sterilizing filters made of asbestos or mem-

brane sheets retain not only yeast cells, but also

the much smaller spores of fungi and even bacte-

ria. Sterilizing filters are also suitable for stopping

fermentation and thus retaining a desired level of

unfermented sugar (residual sweetness) at a se-

lected stage of fermentation.

Suitable measures to prevent crystalline sedi-

ments in the bottle are, e. g., cooling the wine for

a few days to 0–4◦C, addition of metatartaric

acid (cf. 20.2.4), and reducing the concentrations

of potassium, calcium, and tartaric acid by

electrodialysis. Excessive concentrations of

calcium produced by deacidification measures

(cf. 20.2.5.4) can also result in additional crystal

sedimentation (calcium tartrate, calcium mucate,

and calcium oxalate). The elimination of excess

calcium withD-tartaric acid is recommended as

a counter-measure.

20.2.5.4 Amelioration

Must and wine amelioration is required when un-

favorable weather in some years results in grapes

with an excess of acids and a low sugar content.

Such grapes would provide a must which could

not be processed directly into a drinkable, palat-

able wine. The ameliorated wine should contain

neither more alcohol nor less acid than the wine

of the same type and origin from a good vintage

year. The usual procedures involved are the addit-

ion of sugar, deacidification and wine blending.

The addition of sugar (enrichment), for which

regulations exist in most countries, can be car-

ried out before or during fermentation. Sucrose

(dry sweetening) or grape must concentrates are

added. To improve the quality, thesweetness re-

servesof the wine can be raised by the addition

of grape must. The fermentation of this must is

prevented by cold sterile storage, short-time heat-

ing (87◦C) or impregnation with CO 2 (15 g/l,

pressure tank). The bouquet (aroma) is not im-

proved. Poor or inferior wine is not improved by

amelioration. Deacidification is achieved primar-

ily by adding calcium carbonate, which may give

either a precipitate of calcium tartrate or a mix-

ture of calcium tartrate and calcium malate. Un-