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Dear Dr. Vinny,

Why do we call it “malolactic fermentation” when it’s not a fermentation at all, but the conversion of one type of acid to another?

—Jerold G., Fort Myers, Fla.

Dear Jerold,

You’re right that malolactic fermentation (or “ML,” as it’s nicknamed) is a conversion of harsh, tart malic acid to softer, creamier lactic acid. It’s called fermentation, but that’s technically not correct, as fermentation specifically refers to the conversion of sugar to alcohol or acids, not of one acid to another acid.

I do sometimes hear folks refer to it as malolactic conversion and not fermentation, but it seems a little late to try to change a term that is such a part of the winemaking vernacular. My guess is that when ML first got its name, the term “fermentation” was used more broadly to refer to any conversion. So the fermentation of sugar to alcohol is the primary fermentation, and the ML is referred to as the secondary fermentation. Terms tend to stick in language if people use them.

—Dr. Vinny

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