Description (also lactic from the Latin lac = milk) for the typical flavour and also aroma of a wine in the context of a wine talk or wine evaluation. Locally, this flavour is also referred to as bread flavour, butter tone or whey tone. The cause of this flavour is the metabolic product diacetyle, which is formed by lactic acid bacteria as a by-product of malolactic fermentation.
In very small quantities, this substance enhances the flavour of the wine and gives it a creamy and smooth taste with slightly nutty and caramel-like notes. Moderate amounts are up to 1 mg/l in white wine and up to 5 mg/l in red wine. This can mask the fruity flavours of the wine. Only larger quantities of diacetyl can be recognised as a wine defect called lactic acid tartness. Confusingly, this is sometimes also referred to as butyric acidity, but it has nothing to do with butyric acid.
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Egon Mark
Diplom-Sommelier, Weinakademiker und Weinberater, Volders (Österreich)