Lactic acid is the softer, rounder acid that replaces sharp malic acid during malolactic fermentation, when lactic-acid bacteria convert one into the other. The shift lowers total acidity and gives wines a creamier texture and, sometimes, buttery notes (from a related compound, diacetyl). Nearly all reds and many fuller whites, like oaked Chardonnay, undergo it; crisp, fruity whites often avoid it to keep zip.
WHY IT MATTERS FOR COLLECTORS
Lactic, buttery character signals a wine that went through malolactic fermentation — desirable in rich reds and Chardonnay, avoided in zesty whites like Riesling. It explains why some Chardonnays taste creamy and others bracing.
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