Page 80 - Terčelj, Dušan. 2015. The Culture of Wine in Slovenia. Edited by Aleš Gačnik. University of Primorska Press, Koper.
P. 80
he Culture of Wine in Slovenia
Tartaric acid
is the most characteristic acid in must and wine and contributes most to their acidity.
Although noticeable, it is not unpleasant like malic acid or soft like lactic acid. It is
strongest and most stable, although as an organic acid it is still weak in comparison to
inorganic acids. Acid does not serve any energy needs and can be decomposed in wine
only by malolactic bacteria. Tartaric acid can appear freely or is bound to potassium or
calcium. If it is too concentrated, it is excreted as potassium or calcium tartrate, i.e. wine
stone. Metatartaric acid is produced by heating tartaric acid. It is an anhydride of tartaric
acid and serves as a means of preventing wine stone sedimentation. The appearance of
tartaric acid and its quantity in grapes depend mainly on the variety, as well as on the
climatic and soil conditions. Until recently it was the only organic acid which researchers
were unable to synthesise in a laboratory. They used to obtain it from grapes and side
products in winemaking, i.e. wine lees and wine stone.
Malic acid
is present in all fruits. When grapes are fully mature, the ratio between tartaric acid
and malic acid is approximately 1:1. This acid serves the energy needs of the grapevine.
During the ripening of grapes, its quantity is reduced due to the plant’s increased res-
piration and this process increases the warmer the climate. The quantity of malic acid
is partly reduced during fermentation. There are strains of yeast which decompose it.
Malolactic bacteria in wine decompose raw malic acid into a milder tasting lactic acid
and CO2. The salts of malic acid are known as malates.
The following acids are present in wine in smaller quantities:
Citric acid
appears in grape juice in very small quantities. It gives wine a fresh, acidulous flavour. In
nature it is found particularly in citrus fruits. In grape juice there is up to 0.7g of citric
acid per litre. Citric acid salts are known as citrates.
Fatty acids
Most of these appear as the product of yeast activities during fermentation. Higher fatty
acids form aromatic esters with suitable alcohols. Some fatty acids, such as butyric acid,
spoil wine while others, such as capric acid and caprylic acid, give it a pleasant aroma.
Acetic acid
During fermentation, yeasts produce small quantities of acetic acid, but more of it is
produced by lactic acid bacteria from sugar and ethanol. In concentrations over 1g per
litre of wine, it causes an acidic smell and together with alcohols form ester-acetates,
which contribute towards the wine’s aroma.
Lactic acid
appears in small quantities during fermentation and in larger quantities during the
biological freeing of wine from acidity (malic lactic fermentation). Lactic acid is a weak
organic acid, contributing to a pleasant taste and softness. Its salts and esters are known
as lactates.
Amino acids
participate in the creation of aromatic substances with the assistance of yeast and bacteria
converted by amino acids into higher alcohols.
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Tartaric acid
is the most characteristic acid in must and wine and contributes most to their acidity.
Although noticeable, it is not unpleasant like malic acid or soft like lactic acid. It is
strongest and most stable, although as an organic acid it is still weak in comparison to
inorganic acids. Acid does not serve any energy needs and can be decomposed in wine
only by malolactic bacteria. Tartaric acid can appear freely or is bound to potassium or
calcium. If it is too concentrated, it is excreted as potassium or calcium tartrate, i.e. wine
stone. Metatartaric acid is produced by heating tartaric acid. It is an anhydride of tartaric
acid and serves as a means of preventing wine stone sedimentation. The appearance of
tartaric acid and its quantity in grapes depend mainly on the variety, as well as on the
climatic and soil conditions. Until recently it was the only organic acid which researchers
were unable to synthesise in a laboratory. They used to obtain it from grapes and side
products in winemaking, i.e. wine lees and wine stone.
Malic acid
is present in all fruits. When grapes are fully mature, the ratio between tartaric acid
and malic acid is approximately 1:1. This acid serves the energy needs of the grapevine.
During the ripening of grapes, its quantity is reduced due to the plant’s increased res-
piration and this process increases the warmer the climate. The quantity of malic acid
is partly reduced during fermentation. There are strains of yeast which decompose it.
Malolactic bacteria in wine decompose raw malic acid into a milder tasting lactic acid
and CO2. The salts of malic acid are known as malates.
The following acids are present in wine in smaller quantities:
Citric acid
appears in grape juice in very small quantities. It gives wine a fresh, acidulous flavour. In
nature it is found particularly in citrus fruits. In grape juice there is up to 0.7g of citric
acid per litre. Citric acid salts are known as citrates.
Fatty acids
Most of these appear as the product of yeast activities during fermentation. Higher fatty
acids form aromatic esters with suitable alcohols. Some fatty acids, such as butyric acid,
spoil wine while others, such as capric acid and caprylic acid, give it a pleasant aroma.
Acetic acid
During fermentation, yeasts produce small quantities of acetic acid, but more of it is
produced by lactic acid bacteria from sugar and ethanol. In concentrations over 1g per
litre of wine, it causes an acidic smell and together with alcohols form ester-acetates,
which contribute towards the wine’s aroma.
Lactic acid
appears in small quantities during fermentation and in larger quantities during the
biological freeing of wine from acidity (malic lactic fermentation). Lactic acid is a weak
organic acid, contributing to a pleasant taste and softness. Its salts and esters are known
as lactates.
Amino acids
participate in the creation of aromatic substances with the assistance of yeast and bacteria
converted by amino acids into higher alcohols.
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