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Dear Dr. Vinny,

Does malolactic fermentation take place in the barrel or in the bottle? Is it always necessary?

—Paul P., Montreal

Dear Paul,

Malolactic fermentation, also known as "ML," is a secondary fermentation, which means it takes place after the primary fermentation, which converts sugar to alcohol. ML converts harsh malic acid (think of the tartness of a green apple) into softer lactic acid (think of the texture of cream).

ML can take place in a tank, in a barrel, or in a bottle. It's not necessary to the winemaking process, but it's a very popular method. Most red wines and many white wines are intentionally put through ML to enhance stability and complexity.

However, if ML takes place in a bottle, the results can be disastrous. The wine will be cloudy, smelly, and fizzy—really the sort of thing you dump down the sink.

—Dr. Vinny

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