What is malolactic fermentation? Does it occur naturally, or is it artificially induced? Does it change the taste of the wine?

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Dear Dr. Vinny,

What is malolactic fermentation? Does it occur naturally, or is it artificially induced? Does it change the taste of the wine?

—Steven, Boston

Dear Steven,

Malolactic fermentation” (also referred to as "ML," or simply "malo") is technically not a fermentation at all; it's a bacterial conversion. ML is a process that converts harsh, tart malic acid (think of green apples) into creamier, softer lactic acid, which is found in milk (but has nothing to do with lactose—it's perfectly safe for my lactose-intolerant friends!). While ML can occur naturally, it's often initiated by way of a bacterial inoculation.

ML isn’t necessary to winemaking, but it is a way to add complexity and a softer, rounder profile to both red and white wines. It can also add stability—if a wine isn’t encouraged to undergo ML, it might happen spontaneously after the wine is bottled, which can result in a fizzy, cloudy mess.

I think most red wines and many whites are put through ML for stability alone. But you can’t always tell if a wine underwent ML by its taste. For Chardonnays, however, malo can add a richer, buttery profile thanks to diacetyl, an organic compound that is a byproduct of the malolactic conversion.

—Dr. Vinny

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