My diet:

Diacetyl (Butanedione)

No E-numberFlavor enhancersOrigin: Lab-made
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Every diet

VeganYes

The GRAS identity is a chemical synthesis from methyl ethyl ketone.

Gluten-freeYes
HalalYes
KosherYes
KetoYes

It is a flavor, not a sugar.

Low-FODMAPYes
The short answer
Diacetyl is the buttery flavor molecule. The FDA lists it as a GRAS flavor. Breathing the vapor at work has harmed lungs. Eating the trace in a food is the exposure the GRAS rule is about.
Use in moderation

Safe in small amounts; may bother some people or raise blood sugar.

E-numberNone
Comes fromLab-made
What it doesFlavor enhancers
Glycemic index—
Daily limitNot set
Also calledDiacetyl, 2,3-butanedione

Rules by country

🇺🇸 US FDAApproved
🇪🇺 European UnionApproved with limits
🇨🇦 Health CanadaApproved
CaliforniaNo extra rules

The FDA affirms diacetyl as GRAS for use as a flavoring, with no cap beyond good manufacturing practice (21 CFR 184.1278). That rule is about eating it. Inhaling the vapor in a factory is a different exposure: NIOSH has warned that workers who breathe diacetyl, as in some microwave-popcorn plants, can develop a serious lung disease. The EU lists it as a flavoring substance.

Daily limit: Experts haven’t set a number because normal food amounts are far below any level of concern.

What is it?

A tiny amount smells like movie-theater butter. Popcorn oils, candies and margarines have all used it. Real butter contains some too, made by bacteria.

Where it comes from: The FDA describes diacetyl as a yellow liquid, also called 2,3-butanedione, chemically synthesized from methyl ethyl ketone, with the CAS number 431-03-8. In a very dilute water solution it smells like butter. Butter fermentation makes the same molecule in much smaller amounts.

Why it’s in food

  • Gives popcorn a butter aroma
  • Rounds a caramel or a vanilla
  • Flavors margarine and oils
  • Replaces the smell of cultured butter

Often found in

Microwave popcornMargarine and oilsCandyCoffee flavoringsBaked goodsSauces

Also listed as: Diacetyl, 2,3-butanedione, Butanedione, Biacetyl

Health & gut impact

Inhaled at workConcern

NIOSH has documented severe lung disease in workers who inhaled diacetyl vapors from butter flavorings. That is an occupational exposure, not a bite of popcorn.

NIOSH, diacetyl and food flavorings

Eaten as a flavorUnder study

The FDA's GRAS affirmation is for diacetyl as a flavoring used in food, synthesized from methyl ethyl ketone. The rule does not speak to factory air.

21 CFR 184.1278

What can I use instead?

Cultured butter

Ratio: Use the food, not a drop of aroma

Best for: A recipe that can take real dairy

Nutritional yeast

Ratio: It will not taste like butter

Best for: A savory note without this molecule

Related

More flavor enhancers:

Artificial flavors (Artificial flavoring)Artificial flavor means the aroma was synthesized, not extracted from the food it tastes like. The category is allowed. Vegan, halal and kosher status still depends on the carrier.Use in moderationBrewer's yeastBrewer's yeast is yeast left over from making beer. It is bitter, it may contain barley gluten, and it is not the cheesy flake called nutritional yeast.Use in moderationDisodium Guanylate E627Disodium guanylate (E627) is a savory booster used with MSG. It's usually made from yeast, but can come from fish, so check for a vegan label.Generally safeDisodium Inosinate E631Disodium inosinate (E631) boosts savory flavor, usually alongside MSG. It's often made by fermentation but can come from meat or fish, so it's only reliably vegan when labeled.Generally safe

Common questions

Is diacetyl banned?

Not as a food flavor in the US. The FDA still lists it as GRAS. The serious harm on record is from workers inhaling it.

Does butter contain diacetyl?

Cultured butter contains some, made by bacteria. The ingredient on a popcorn bag is the purified flavor.

Is Diacetyl safe?

Use in moderation (52/100). The FDA affirms diacetyl as GRAS for use as a flavoring, with no cap beyond good manufacturing practice (21 CFR 184.1278). That rule is about eating it. Inhaling the vapor in a factory is a different exposure: NIOSH has warned that workers who breathe diacetyl, as in some microwave-popcorn plants, can develop a serious lung disease. The EU lists it as a flavoring substance.

Is Diacetyl vegan?

Yes. The GRAS identity is a chemical synthesis from methyl ethyl ketone.

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Scientific sources & regulatory citations
  • 21 CFR 184.1278 (US FDA)
  • NIOSH, diacetyl and food flavorings
  • 21 CFR 184.1278

CAS 431-03-8