Today’s Wine Word: Malolactic Fermentation


Well, there’s a mouthful of a wine word! Not to worry – it’s easier to understand than it is to pronounce it. And, now seems like a good time to take a look because, even as we speak, lots and lots of wines being made in the northern hemisphere are bubbling their way through what’s often called the second fermentation – the malolactic fermentation, or ML for short.

For the microbiologists out there I’ll say that it’s not really a fermentation – it’s a conversion.

The real point? Do you like your Chardonnay buttery? If so, it’s very likely that the brands you prefer put their Chard through ML or partial ML.

The conversion normally follows the primary, alcoholic fermentation.

It’s routine for reds, for the sake of stability and to soften the acid. When it comes to whites, it’s more of a question mark and when the topic comes up it’s usually in reference Chardonnay. Here’s how it goes:

It may take the wine maker about three weeks to make his Chardonnay. Then, lactic-acid bacteria is added to the new wine. It causes the tart malic acid – the green apple acid, to convert to soft lactic acid – the milk acid. So the wine feels softer and rounder on your palate. ML also has a byproduct, called diacetyl, which adds a sort of viscous, oily sensation to the texture and smells and tastes buttery.

TRIVIA! Diacetyl is the substance they add to microwave popcorn to make it buttery!

The wine maker might choose to go with ML to reduce the acidity or because he wants the buttery character or both. Depending upon his stylistic goals he can do ML for only some of the wine and blend it with non-ML wine. It’s a question of how high the acid is, to begin with, and how much of it is malic – what’s the acid level going to be when it’s all over? It’s especially important for whites to have a refreshing, lively acidity.

It’s a matter of stylistic preference. Some wine makers love the buttery character and think of it as a complement to the wine. Others might call it a competition or feel that it takes away from freshness. In cool climates, where the acid is sometimes painfully high to begin with, ML is an excellent tool for rounding the wine out a bit.

Sometimes the winemaker notes refer to a partial malolactic fermentation. They’re saying that the wine maker decided on a compromise. If he made ten barrels of Chardonnay, maybe four of them were put through ML. He’ll blend that wine with the non-ML wine to reach a nice balance of fruity to buttery character and a sound acidity.  

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