Page 83 - Terčelj, Dušan. 2015. The Culture of Wine in Slovenia. Edited by Aleš Gačnik. University of Primorska Press, Koper.
P. 83
The Components of Wine
juice its viscosity. The hybrid grape Šmarnica, for example, has plenty of pectins. When
we squeeze one of its grapes, we are left with the skin, while the grape retains its shape
and the juice does not separate. During fermentation, pectins decompose into methyl
alcohol. Usually, some of this alcohol is found in wine, but in such small quantities that
it is not harmful.
Nitrogen substances28
are an important component of grape juice. There is inorganic nitrogen (NH4), which
yeasts consume, and organic nitrogen that consists of amino acids, polypeptides and
proteins. Polypeptides are amino acids bound into a number of molecules and make up
60 to 90 percent of the total nitrogen. Proteins are made from amino acids, bound into
large molecules and have the character of colloids. In their insoluble state they spoil
the appearance of wine. In bottled wine they can change from soluble into insoluble
form, therefore it is beneficial if they are extracted as soon as possible (from must or
at least later from wine). They are removed if bentonite is added, i.e. pure clay, as it
extracts proteins.
Amino acids
are consumed by yeasts during the phase of multiplication. Out of amino acids yeasts
make higher alcohols that later bind into aromatic substances. Some toxic nitrogen
substances, such as ethyl carbamate and histamine, appear in such small quantities that
they are not harmful to health.
Enzymes
are the catalysts of biochemical processes. They are involved in every biochemical
change. There are a great number of them and they are divided into two basic groups:
oxidising enzymes and hydrolytic enzymes.
Vitamins
are present in both must and wine. They are required for yeast growth. In grapes, the main
vitamins present are vitamin C (ascorbic acid) and the whole group of B vitamins.
Minerals
are usually present in grapes in the form of salts. The main mineral in grapes is potassium
(approximately 50 percent). It is bound to wine acid into potassium tartrate. When it
changes into an oversaturated form, it crystallises and is excreted as wine stone. After
fermentation it coats the vessels and bottles in which wine is stored with small crystals,
which can confuse a layperson. Juice also contains sodium, calcium and magnesium.
Anions are present in the form of salt (sulphates, chlorides and phosphates). Must also
contains small quantities of iron, copper, aluminium, zinc, manganese, boron and
silicon, and miniscule traces of arsenic, cadmium and lead.
These are just the main groups of substances present in must that carry over to wine. But
just a short description of a few substances gives the reader the idea of the wealth of good-
ness that grapes bring to wine.
28 T he author was the first in the world to determine quantitatively the nucleic composition of nitrogen (bases,
nucleosides and nucleotides) in Sauvignon from Ormož and published his findings in 1965 in Annales de
Technologie Agricole, INRA, Paris, 1965: pp. 307-319.
79
juice its viscosity. The hybrid grape Šmarnica, for example, has plenty of pectins. When
we squeeze one of its grapes, we are left with the skin, while the grape retains its shape
and the juice does not separate. During fermentation, pectins decompose into methyl
alcohol. Usually, some of this alcohol is found in wine, but in such small quantities that
it is not harmful.
Nitrogen substances28
are an important component of grape juice. There is inorganic nitrogen (NH4), which
yeasts consume, and organic nitrogen that consists of amino acids, polypeptides and
proteins. Polypeptides are amino acids bound into a number of molecules and make up
60 to 90 percent of the total nitrogen. Proteins are made from amino acids, bound into
large molecules and have the character of colloids. In their insoluble state they spoil
the appearance of wine. In bottled wine they can change from soluble into insoluble
form, therefore it is beneficial if they are extracted as soon as possible (from must or
at least later from wine). They are removed if bentonite is added, i.e. pure clay, as it
extracts proteins.
Amino acids
are consumed by yeasts during the phase of multiplication. Out of amino acids yeasts
make higher alcohols that later bind into aromatic substances. Some toxic nitrogen
substances, such as ethyl carbamate and histamine, appear in such small quantities that
they are not harmful to health.
Enzymes
are the catalysts of biochemical processes. They are involved in every biochemical
change. There are a great number of them and they are divided into two basic groups:
oxidising enzymes and hydrolytic enzymes.
Vitamins
are present in both must and wine. They are required for yeast growth. In grapes, the main
vitamins present are vitamin C (ascorbic acid) and the whole group of B vitamins.
Minerals
are usually present in grapes in the form of salts. The main mineral in grapes is potassium
(approximately 50 percent). It is bound to wine acid into potassium tartrate. When it
changes into an oversaturated form, it crystallises and is excreted as wine stone. After
fermentation it coats the vessels and bottles in which wine is stored with small crystals,
which can confuse a layperson. Juice also contains sodium, calcium and magnesium.
Anions are present in the form of salt (sulphates, chlorides and phosphates). Must also
contains small quantities of iron, copper, aluminium, zinc, manganese, boron and
silicon, and miniscule traces of arsenic, cadmium and lead.
These are just the main groups of substances present in must that carry over to wine. But
just a short description of a few substances gives the reader the idea of the wealth of good-
ness that grapes bring to wine.
28 T he author was the first in the world to determine quantitatively the nucleic composition of nitrogen (bases,
nucleosides and nucleotides) in Sauvignon from Ormož and published his findings in 1965 in Annales de
Technologie Agricole, INRA, Paris, 1965: pp. 307-319.
79
