Q: I recently read that some Chardonnays get their buttery flavor from a chemical compound called diacetyl. Is it harmful at all? —Orville, Brazil, Ind.
A: You are correct that diacetyl is the chemical compound responsible for some of the buttery flavors in certain Chardonnays. It occurs organically, but it can also be artificially manufactured. The diacetyl found in wine is of the organic variety, a natural by-product of malolactic conversion, which converts sharper malic acid into softer, creamier lactic acid and also produces diacetyl. This naturally occurring diacetyl poses no health risk in the quantities associated with moderate wine consumption.
However, artificially manufactured diacetyl—used as a flavor additive in some foods, most notably microwave popcorn—has been shown to pose a health risk when people are exposed to its smell at high concentrations for extended periods of time. The issue came to light in 2000 when the National Institute for Occupational Safety and Health, part of the CDC, investigated an unusually high instance of a rare lung disease among former employees of a popcorn-packaging plant in Missouri. They discovered that while adding flavorings to the popcorn, the workers had been inhaling heated diacetyl vapors that emanated from the additives, causing permanent lung damage in the form of bronchiolitis obliterans. The condition manifests as shortness of breath, wheezing, dry cough and fatigue, and has since been known more commonly as "popcorn lung."
As a wine drinker (who presumably does not work in a popcorn factory), however, you need not fear buttery-tasting wines. The diacetyl present in wine is organic, not heated, occurs in small amounts and is only inhaled for a very brief period of time.