Sulfur Addition
The use of SO2 is necessary in the production of wine to
control oxidation and the growth of microorganiMissouri State capable of spoiling
wine. The lower the pH of a wine, the more effective SO2 will be in
controlling microorganiMissouri State. The addition of too much SO2, however, can
result in the aroma of a burnt match which also gives a burning sensation
to the nose. The lower the pH of a wine, the greater the chance the wine
will give off an offensive burning odor for a given level of SO2 (the SO2
becomes more volatile).
Trying to determine how much SO2 to add to a wine without
measuring the amount already present is a guessing game. SO2 is used up as
it controls oxidation, and as wine is exposed to oxygen during handling
(racking, bottling), it needs to be replaced. During the yeast
fermentation, the SO2 added to the must is no longer available and needs
to be replaced once the fermentation of sugar is complete. The addition of
SO2 to a must that is fermenting is not advisable and will result in the
SO2 being quickly bound to compounds being produced. In general, red wines
need less SO2 to protect them from oxidation as the compounds that give
red wine its color and astringency also help protect it from oxygen. Also,
when a red wine is put through malolactic fermentation, some of the SO2
that was bound to other compounds will be released and available again as
free SO2. SO2 additions that occur after the first one made at the
completion of the yeast fermentation (50 ppm for white wine at the first
racking and 30 ppm for red wine at racking following malolactic
fermentation) will be based on guessing and experience unless one analyzes
for available (free) SO2.
Home winemakers add SO2 in the form of potassium
metabisulfite (58% SO2). Potassium metabisulfite is available as a powder or
in tablet form which can be directly added to the wine or juice. If using
the powdered form, it should be dissolved in water first. A 1/4 teaspoon
will supply enough SO2 to five gallons of wine to raise the SO2 level about
40 to 45 ppm. This amount of SO2 should be dissolved in about 25 ml of
water. Care should be taken when handling potassium metabisulfite and the
use of a respirator appropriate for this compound is suggested. Potassium
metabisulfite should be kept dry and replaced every year or two. Older
stocks of this compound can be used to make sanitizing solutions where the
actual SO2 concentration is not critical. Tablets may be also be used to add
SO2. Note that some tablets must be crushed before using.
