Do you like your chardonnay like you like your popcorn – rich and buttery? That may be diacetyl you’re snuffling. Diacetyl is a compound that is naturally present in wines that undergo malolactic fermentation, which is commonly referred to as “ML” or “secondary fermentation.” In other words, after yeast turn grape juice sugars into alcohol (aka “primary fermentation”), a strain of bacteria turns malic acid in the wine into lactic acid.
But what’s the difference between the two acids? Well, malic acid is tart – think green apple jolly ranchers. Lactic acid is milder – you find it in yoghurt, sourdough starters, cultured butter, etc.
The lactic acid bacteria that conducts ML in wine produces more than just lactic acid – most strains also degrade citric acid to produce diacetyl. How much diacetyl is produced depends on a few thins:
- The particular strain of bacteria
- The amount of citric acid that was present in the wine to begin with
- Various fermentation conditions
Some yeast strains even produce diacetyl during primary fermentation.
Of course, drinking something you may not know how to pronounce can be scary (unless it’s Châteauneuf–du–Pape). But that doesn’t mean everything with a chemical name is dangerous. Per the FDA, health risks of diacetyl are limited to inhaling high concentrations of the compound. Unless you work in a factory producing microwave popcorn, you should not be concerned.
Most red wines undergo ML and accordingly contain diacetyl as well. However, the sensory detection threshold for diacetyl in red wines is higher than it is for white wines. Thus, few syrahs are described as “buttery.”
And if you’re wondering why your sauvignon blanc smells more like the grass that cows eat than the butter produced from their milk, it’s because winemakers rarely put sauvignon blanc and other white wines through ML (at least, not on purpose). We save that dubious honor for chardonnay.
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