Diacetyl

Diacetyl is a buttery-tasting compound that is a by-product of malolactic fermentation, the process in which beneficial bacteria turn sharp-tasting malic acid in wine to softer lactic acid. Chardonnays that have gone through malolactic fermentation often have noticeable diacetyl. Butteriness in chardonnay does not come from oak; although many wine drinkers assume this is the case.