Arginine, usually one of the most abundant yeast available amino acids in grape juice, is taken up by wine
yeast as a nutrient and may be metabolized yielding urea if present in excess amounts. If the urea can
not be further metabolized and accumulates above a critical concentration, yeast strains release it from
their cells into the wine during or at the end of fermentation. Urea can spontaneously react with the
alcohol in wine to form EC. The chemical reaction between urea and ethanol is exponentially
accelerated at elevated temperatures. To a lesser extent citrulline, an amino acid which is not
incorporated into yeast protein, and is formed during arginine biosynthesis, can serve as an EC precursor.
Lactic acid bacteria can also be a source of citrulline under winemaking conditions.
However, the key reaction for EC formation in wine is between urea and ethanol.
Arginine, usually one of the most abundant yeast available amino acids in grape juice, is taken up by wine
yeast as a nutrient and may be metabolized yielding urea if present in excess amounts. If the urea can
not be further metabolized and accumulates above a critical concentration, yeast strains release it from
their cells into the wine during or at the end of fermentation. Urea can spontaneously react with the
alcohol in wine to form EC. The chemical reaction between urea and ethanol is exponentially
accelerated at elevated temperatures. To a lesser extent citrulline, an amino acid which is not
incorporated into yeast protein, and is formed during arginine biosynthesis, can serve as an EC precursor.
Lactic acid bacteria can also be a source of citrulline under winemaking conditions.
However, the key reaction for EC formation in wine is between urea and ethanol.
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