If malolactic fermentation makes wines buttery, and red wines undergo it, why aren't red wines buttery?

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Dear Dr. Vinny,

Why don’t you find buttery flavors in red wines that have undergone malolactic fermentation?

—John, Milford, Mich.

Dear John,

Let me first run through the basic ideas here so everyone can follow along. "Malolactic fermentation" isn’t technically a fermentation at all—it’s a bacterial conversion. There are three main reasons to make a wine go through “ML” or “malo,” which converts tart malic acid into creamier, softer lactic acid. ML can reduce a wine’s acidity, stabilize it (by ensuring the conversion doesn’t happen spontaneously later), and to shape the flavors, aromas and textures. ML can occur naturally, or winemakers will initiate it intentionally by inoculating the bacteria into wine.

You’re right that some whites that go through ML can have a buttery or sweet cream note to them, caused by diacetyl, a byproduct of ML. But then why don’t all wines that go through ML also taste buttery? Most reds do go through ML, and many whites, unless they are purposefully made in a crisper style that can take advantage of that malic acid.

There are two main reasons. First, winemakers have a handful of choices when it comes to ML that will affect how it influences a wine—deciding at what point during (or after) primary fermentation, whether or not it occurs in a barrel, and which version of the bacterial strain to inoculate with (there are several to choose from) will all have an effect on how ML affects a wine.

Second, studies have indicated that the magnitude of the perception and influence of diacetyl can depend on the wine itself. Most wines will have the creamy texture effect from ML, but while diacetyl in whites manifests as buttery notes, in reds wines that go through ML, instead of buttery, they taste fruitier, with more berry flavors.

—Dr. Vinny

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