The
Acidity in Wine
Acidity, according to The Oxford Companion to Wine, is
“a general term for the fresh, tart, or sour taste produced by the
natural organic acids present in a liquid. Wines, together with
most other refreshing or appetizing drinks, owe their attractive
qualities to a proper balance between this acidic character and the
sweet and bitter sensations of other components.” p4.
Without the proper acid balance in a wine, it tastes flat and
ordinary. “Flabby” is a word that winemakers use. If the acid is
too high, the wine tastes tart. Wine acidity is usually measured in
grams per litre, total acidity (TA) and pH. This information
usually not on a wine label, although most detailed tasting notes
put out by wineries will sometimes give the pH.
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The Acids Found in Wine
The main acids in wine are:
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The main acids in wine are tartaric acid and malic acid. The
relative amounts of each these acids depends on the grape variety
and where the grape is grown.
Volatile Acidity
One acid that is not desirable in wine is acetic acid – or
vinegar. Winemakers refer to this undesirable acid as “VA” or
volatile acidity. It is called “volatile” because it boils off when
heated. Tartaric and malic acid does not boil off when wine is
heated and so are called “non-volatile.” High VA can ruin a wine.
The Effect of Climate on Acid and Sugar
The tartaric and malic acids in grapes develop naturally as the
grape ripens. The warmer the climate, however, the more these acids
are lost through the vine’s respiration. In general, grapes grown
in warmer climates have a lower acidity than grapes grown in cooler
climates. Thus a Margaret River chardonnay, for example, will have
a higher natural acid balance than, say, a Hunter Valley
chardonnay.
The other essential process that occurs in the grape as it ripens
is sugar production. This is the opposite of acid production:
grapes grown in warmer climates have a higher sugar content that
grapes grown in cooler climates. Sugar content of grape juice is
expressed in “degrees Beaume” where 1 degree Beaume is approximately
equal to 1% alcohol when the wine is fermented to dryness. That is,
grapes that are 14 degrees Beaume when picked will usually produce a
wine that is 14% alcohol when all the sugar is fermented.
The interaction between acid and sugar balances is this:
In France, for example, areas such as Chablis are cool regions
and normally produce grapes with low sugar and high acid. In such
areas, getting enough sunlight and warmth for raising sugar levels
are a concern. In low sugar years, winemakers in these areas add
sugar to the grape juice. The process is called chaptalization.
The addition of sugar in winemaking is illegal in Australia. It
is not much of an issue, however, because most areas of Australia
have enough sunlight to ripen grapes.
Australia, in fact, has the opposite problem. Often there is so
much sunlight that the acid drops too fast as the sugar levels
increase. In Australia, although adding sugar is illegal, it is
permissible to add tartaric acid if the acid has dropped to rapidly
in the grapes.
How Malolactic Fermentation Affects Acidity
Malolactic fermentation, otherwise known as “MLF” or “Malo” is a
winemaking process that has an effect on a wine’s acidity.
Malolactic fermentation does pretty much what it sound like: it
converts malic acid into lactic acid. MLF has the result of
lowering the acidity of a wine. The effect on a wine depends on how
much malic acid is present in the wine to start with. A chardonnay
from Burgundy usually has less malic acid that a chardonnay from
Margaret River. So MLF in the burgundy does not usually lower the
acid as much as a similar MLF in the Margaret River wine. MLF in
the Margaret River wine significantly alters the flavour profile.
Wine acidity is important to balance the alcohol. In sweet
wines, it is also important to balance residual sugar.
Total Acidity
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Total acidity
is the measure of total acids in the wine. A high TA would be
1.0%. This is quite tart to taste. A low TA of, say 0.4%,
would be the opposite: a flat tasting wine. Red wines are
usually around 0.6% and white wines are a little higher.
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pH
pH is the measure of the acidity of the wine. It is not a
sliding scale, but a logarithmic scale – like the Richter scale used
to measure earthquakes. Thus, a wine with a pH of 3 is ten times
more acidic than a wine with a pH of 4. The higher the pH, the
lower the acidity.
Total acidity and pH are both ways of measuring acidity, but they
are different ways of measuring acidity.
Typical pH and TA Levels
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A typical premium Margaret River chardonnay has
a total acidity of 0.58 grams per 100 mL (0.58%) and a pH of
about 3.4. Residual sugar would be around 2% or less
(undetectable). A sweet wine might have a total acidity of 1
gram per 100 mL (1%) and a pH of 3 and a residual sugar level of
15% (very apparent). |
Summary
- The principal acids of wine are tartaric and malic.
- Volatile acidity (undesirable) is due to acetic acid
(vinegar).
- Cool climate grapes have high acid and low sugar.
- Warm climate grapes have low acid and high sugar.
- Malolactic fermentation can be used to lower acidity of wine.
- Total acidity is reported as grams of tartaric acid per 100 mL
of wine.
- Table wines generally have a total acidity of 0.6 to 0.7%.
- Sweet white dessert wines generally have a total acidity above
1% to balance the sugar.
- pH is a measure of "active" acidity.
- The lower the pH, the higher the acidity; the higher the pH,
the lower the acidity.
- Table wines generally have a pH between 3.3 and 3.7.
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