Diacetyl is an organic substance that imparts a rich, buttery flavor. Although it occurs naturally in some foods, most of the diacetyl in the human diet is artificially manufactured and used to flavor processed food products.

Diacetyl is the main flavoring agent in margarine, shortening, oil sprays and most other artificially flavored butter substitutes. It’s widely used in microwave popcorn, potato chips, corn chips and crackers, but it’s also frequently found in cookies, chocolate, cocoa-flavored products, candy, gelatin desserts, flour mixes, flavored syrups and prepackaged frosting. Sauces, soft drinks, chewing gum and ice cream are other common sources.

Diacetyl is found in real butter, too. It’s the main flavor agent in the starter cultures used to make butter, according to a report by the National Toxicology Program. Minute amounts of the compound are also naturally present in milk, yogurt, cheese, coffee, honey and most fruits. Because diacetyl is a natural product of alcohol fermentation, it is often found in beer and wine.

Although diacetyl has been linked to a high prevalence of acute lung disease in industrial workers that handle the flavoring, the U.S. Food and Drug Administration recognizes it as generally safe for consumption. On food labels, diacetyl is typically listed under the blanket term “artificial flavors.”