2009_Book_FoodChemistry

918 20 Alcoholic Beverages
stability and hence for the quality of the wine. Efforts
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. Furthermore,
multivalent metal ions can cause discoloration
and sediments. Wine clarification is
usually achieved by precipitation reactions, filtration
or centrifugation. In blue-fining the excess
metal ions which are responsible for metalinduced
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, ironfree
bentonite, kaoline, agar-agar and purified or
activated charcoals are added to the wine. This
results in adsorption or precipitation of the substances
causing cloudiness and unpleasant taste,
the interaction products all being quick-settling
coagulums. Phenolic compounds are removed
from wine by polyvinylpyrrolidone (detanninizing)
and undesirable sulfur compounds by cupric
sulfate.
The clarification by filtering involves pads of asbestos,
cellulose, infusorial earth, and filter aids
such as Hyflo Super Cel and Filter Cel. The filters
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 membrane
sheets retain not only yeast cells, but also
the much smaller spores of fungi and even bacteria.
Sterilizing filters are also suitable for stopping
fermentation and thus retaining a desired level of
unfermented sugar (residual sweetness) at a selected
stage of fermentation.
Suitable measures to prevent crystalline sediments
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 with D-tartaric acid is recommended as
a counter-measure.
20.2.5.4 Amelioration
Must and wine amelioration is required when unfavorable
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, palatable
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 addition
of sugar, deacidification and wine blending.
The addition of sugar (enrichment), for which
regulations exist in most countries, can be carried
out before or during fermentation. Sucrose
(dry sweetening) or grape must concentrates are
added. To improve the quality, the sweetness reserves
of the wine can be raised by the addition
of grape must. The fermentation of this must is
prevented by cold sterile storage, short-time heating
(87 ◦ C) or impregnation with CO 2 (15 g/l,
pressure tank). The bouquet (aroma) is not improved.
Poor or inferior wine is not improved by
amelioration. Deacidification is achieved primarily
by adding calcium carbonate, which may give
either a precipitate of calcium tartrate or a mixture
of calcium tartrate and calcium malate. Un-