Sugar and Acid in Wines - Wine Charateristics
The dry table wines of Bordeaux and of Burgundy, of the Medoc and the
Cotes du Rhone, of the Hunter River valley and the Barossa, of Spain,
Italy, Algeria, California, South Africa and Chile and of a dozen other
countries, all have the common characteristic, or should have if
properly made, of containing no trace of unfermented sugar.
". . . Having no unfermented sugar", is what is meant by the
description, dry. Conversely, if the wine contains unfermented or
residual sugar, or if sweetening has been added, then the wine is
classified as sweet. Of course there are exceptions; some dry red wines
do contain a very little residual sugar, but generally this is
accidental, certainly it is not the intention of the winemaker for there
 is a real danger that an unfortified wine containing a little sugar
could start a new ferment at some period of its cask or bottle life. To
be precise, the sugar remaining in a fully fermented dry wine should not
be in excess of one part in 500 (0.2 percent).
Proper fermentation and careful handling from fermenting vat to bottle
will ensure that the wine is dry, but if the winemaker is still
uncertain of his wine, he may pasteurize it by passing it through heated
pipes in which it spends a few minutes at 140deg. This kills any yeasts
present and many of the harmful bacteria.
The dryness of a wine therefore is the absence—or the presence of only
minute quantities—of sugar. The palate detects the dryness of the wine,
or the degree of sweetness, the point being that there is no degree of
dryness; it is completely dry, or it is sweet. "But," you will say, "I
have tasted some dry wines that are not as dry as others, or at least,
they taste sweeter." Of course you have, but this is not due to the
presence, or absence of sugar; it has to do with those all-important
factors in wine, the acids.
If the wine is deficient in acids, or there is too much of one acid at
the expense of another, the wine is said to be out of balance. Too
little acid will leave the wine soft, or bland, lacking in decisive
taste that a good dry wine should have. This frequently happens in wine
made from grapes that have been allowed to ripen too long on the vine.
The acids have been used up in forming sugar and the result is colored
water and alcohol.
The wine also may be out of balance because there is too much acid. If
this is caused by picking the grapes too early, another effect will be
low alcohol content. But there are many other possible causes of acid
imbalance, the commonest of which is excessive acetic acid, caused by
the entry into the fermenting or fermented wine of the bacteria known as
acetobacter, which converts alcohol into acetic acid, or vinegar. Once
acetic acid enters the wine (as distinct from that naturally present in
the juice) the wine will taste vinegary, and there is nothing the
winemaker can do about it. The simplest and most effective way to
prevent the entry of acetobacter is to separate the fermented wine as
quickly as possible from the mare and get it into casks which are kept
full and bunged, thus preventing the entry of air which carries the
acetobacter.
 Another acid which has a pronounced effect on the flavor, and the
keeping quality, of the wine is tartaric. If there is not enough
tartaric acid in the wine it will taste insipid, if there is too much it
will be hard. Excess salt of tartaric acid may be removed by
refrigeration, a practice common with white wines. With dry reds, time
will often correct excessive amounts of tartaric acid which forms into
crystals and settles, provided the wine is kept cool. Careful decanting
of the wine solves the problem. The crystalline deposit into which it
forms has no effect on the taste of the wine, only on its appearance.
The common word to describe it is "crust", unobjectionable in dry red,
indeed acceptable, for it indicates that the wine has been aged in
bottle.
Another important acid in wine is malic, and again it will depend on the
degree of ripeness of the grapes when picked as to how much malic acid
is left in the wine. Often there is as much malic as tartaric acid and
it is a valuable component in the balance of the finished wine. But this
acid is prone to attack by the gracile bacteria, which turn it into
lactic acid. This usually happens in the bottle and the process is known
as malolactic fermentation. Sometimes it is deliberately induced for a
little malolactic fermentation tends to freshen the wine, while at the
same time reducing its acidity. There are some rose wines from Spain on
the Australian market today that show strong evidence of malolactic
fermentation. As one of the products of malolactic fermentation is
carbon dioxide, tiny bubbles will be seen and the tongue will detect
them. Indeed, the rose wines of Spain that contain the tiny bubbles are
popular. Although the malolactic fermentation that produced them has
lowered the acidity of the wine and, to a degree, unbalanced it, the
resulting freshness and tang of the bubbles on the tongue give these
Moses a distinctive character.
 The acidity of a finished wine will depend on where it is grown and when
the grapes were picked. Generally, the wines from very hot districts are
lacking in acid, and sometimes in color, but there are devices to which
the winemaker may resort to correct this lack. The addition of calcium
phosphate will increase acidity, but the proper way to ensure correct
acid content and balance is to pick the grapes at exactly the right time
when all the acids and sugars are present in the juice in the right
proportions. No amount of adjustment of the wine, once it is made, will
replace sound farming judgment of when to take the crop off the vines
and put it into the fermenting vats. But the wrong decision, to pick too
early or too late, may be as much a matter of avarice as of expert-ness,
for over-ripe grapes usually contain more juice and more sugar and make
more and stronger wine, but at the expense of balance.
Some of the wines from the hot irrigation districts of Australia show
con-siderable lack of balance, their acids quite out of proportion. The
temptation must be great to increase just a little more the already very
high yield from irrigated vineyards. When this is combined with
fermentation at too high temperatures, a common fault in vineyards that
do not have modern refrigera-tion equipment or must correct lack of
color by hot fermentation, the wines are often soft and flabby, good
only as base blending material or for making into sparkling wines by the
impregnation method.
As a rule, it is easier to make a sound dry red wine than a dry white.
The red, fermented with its skins, takes strength and flavor and keeping
quality from them; a dry white must derive all its qualities from the
juice only, being parted from its skins before fermentation starts and,
in consequence, is more delicate, requiring much more careful handling.
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