Leucine
Due to their esterase activities, yeasts form various esters (a few milligrams per liter). The most important acetates of higher alcohols are isoamyl acetate (banana aroma) and phenylethyl acetate (rose aroma). Although they are not linked to nitrogen metabolism, ethyl esters of medium‐chain fatty acids are also involved. They are formed by the condensation of acetyl‐CoA. These esters have more interesting aromas than the others. Hexanoate has a flowery and fruity aroma reminiscent of green apples. Ethyl decanoate has a soap‐like odor. In white winemaking, the production of these esters can be increased by lowering the fermentation temperature and increasing must clarification. Certain yeast strains (71B) produce large quantities of these compounds, which contribute to the fermentation aroma of young wines. They are rapidly hydrolyzed during their first year in bottle and have no long‐term influence on the aroma of white wines.
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