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IUPAC name 2,3-Butanedione
Other names Diacetyl
CAS number 431-03-8
PubChem 650
Molecular formula C4H6O2
Molar mass 86.0892 g/mol
Appearance Yellowish green liquid
Density 0.990 g/mL at 15 °C
Melting point

-2 to -4 °C

Boiling point

88 °C

Solubility in water Soluble in 4 parts
MSDS External MSDS
Main hazards Harmful, flammable
R-phrases R10 R22 R36 R37 R38
S-phrases S9 S16 S33
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Diacetyl (IUPAC systematic name: butanedione or 2,3-butanedione) is a natural byproduct of fermentation. It is a vicinal diketone (two C=O groups, side-by-side) with the molecular formula C4H6O2.


In food products

Diacetyl, along with acetoin, is one of the compounds that gives butter its characteristic taste. Because of this, manufacturers of margarines or similar oils based products typically add diacetyl and acetoin (along with beta carotene for the yellow color) to the final product, which would otherwise be tasteless.[2]

In alcoholic beverages

At low levels in alcoholic beverages, it contributes a slipperiness to the feel of the beer or wine in the mouth. As levels increase, it imparts a buttery or butterscotch flavor (butterscotch itself may be devoid of diacetyl).

It is produced during fermentation as a byproduct of valine synthesis. During this synthesis yeast produces α-acetolactate, which escapes the cell and is spontaneously decarboxylated into diacetyl. The yeast then adsorbs the diacetyl, and reduces the ketone groups to form acetoin and 2,3-butanediol, relatively flavorless compounds.

Beer sometimes undergoes a diacetyl rest, which entails elevating temperature slightly for two or three days after fermentation is complete, to allow the yeast to absorb the diacetyl it produced earlier in the fermentation cycle. The makers of some wines, such as chardonnay, deliberately promote the production of diacetyl because of the feel and flavors it imparts. It is present in many California chardonnays known as "Butter Bombs," although there is a growing trend back toward the more traditional French styles.[citation needed]

Concentrations from 0.005 mg/L to 1.7 mg/L were measured in chardonnay wines, and the amount needed for the flavor to be noticed is at least 0.2 mg/l.[3][4]


Worker safety

The United States National Institute for Occupational Safety and Health has suggested that diacetyl, when used in artificial butter flavoring (as used in many consumer foods), may be hazardous when heated and inhaled over a long period.

Workers in several factories that manufacture artificial butter flavoring have been diagnosed with bronchiolitis obliterans, a rare and serious disease of the lungs. The cases found have been mainly in young, healthy, non-smoking males. There are no known cures for bronchiolitis obliterans except for lung transplantation.

While several authorities have called the disease "Popcorn Worker's Lung," a more accurate term suggested by other doctors may be more appropriate, since the disease can occur in any industry working with diacetyl: diacetyl-induced bronchiolitis obliterans.

After the workers filed a lawsuit against the manufacturers, the United States Environmental Protection Agency began an investigation into the chemical properties of microwave popcorn butter flavoring. In March 2004, former microwave popcorn plant employee Eric Peoples, of Joplin, Missouri, was awarded $20 million for permanent lung-injuries sustained while on the job.[5] On July 19, 2005, jurors awarded $2.7 million to another popcorn plant worker in Missouri for his claim of diacetyl-induced respiratory problems.[6]

On July 26, 2006, the International Brotherhood of Teamsters and the United Food and Commercial Workers petitioned the U.S. Occupational Safety and Health Administration to promulgate an emergency temporary standard to protect workers from the deleterious health effects of inhaling diacetyl vapors.[7] The petition was followed by a letter of support signed by more than thirty prominent scientists.[8] The matter is under consideration.

There are currently two bills in the California Legislature to ban the use of diacetyl.[9][10][11]

Consumer safety

Dr. Cecile Rose, pulmonary specialist at Denver's National Jewish Medical and Research Center, in a letter, warned federal agencies or regulators that consumers, not just factory workers, are in danger of suffering the fatal popcorn lung disease from buttery flavoring fumes in microwave popcorn. David Michaels of the George Washington University School of Public Health first published Rose's letter on his blog.[12][13] However, the only sample data known-to-date is the case where a consumer, who ate at least two bags of buttery microwave popcorn daily for 10 years, became diagnosed with the same disease affecting workers exposed to the substance, bronchiolitis obliterans.[14] His lung problems were linked to breathing the vapors; although rare, the reported man's kitchen also had diacetyl levels comparable to those in popcorn plants.[15]

The Flavor and Extract Manufacturers on September 4, 2007, recommended reduction of diacetyl in butter flavorings. The Weaver Popcorn Company of Indianapolis has replaced the butter flavoring with a new ingredient.[16] Weaver makes the Trail's End brand of popcorn sold by the Boy Scouts of America. A ConAgra spokesperson has said it will do the same in a year,[17] and is working to remove the ingredient from its popcorn products. [18]

In a Reuters story dated September 5, 2007, writer Julie Steenhuysen quoted the spokeswoman for ConAgra Foods Inc, maker of Orville Redenbacher and Act II microwave popcorn brands, saying "it will drop diacetyl from its butter-flavored microwave popcorn in the near future." [19]

EU Regulation

The EU Commission has declared that diketones (for example acetylacetone, CH3COCH2COCH3) are like dialcohols and hydroxyketones in that they are in vitro and in vivo genotoxic chemical substances and therefore have been forbidden as nutrition additives since 2005.[20]

As diacetyl is a diketone (in fact the simplest) it may eventually be subject to this EU regulation.[citation needed]

See also

  • Bronchiolitis obliterans


  1. ^ Merck Index, 11th Edition, 2946.
  2. ^ Pavia et al., Introduction to Organic Laboratory Techniques, 4th ed., ISBN 978-0-495-28069-9
  3. ^ JC Nielsen, M Richelieu. Control of Flavor Development in Wine during and after Malolactic Fermentation by Oenococcus oeni. Appl Environ Microbiol. 1999 February; 65(2): 740–745.
  4. ^ B Martineau, T Henick-Kling, T Acree (1995). Reassessment of the Influence of Malolactic Fermentation on the Concentration of Diacetyl in Wines. Am Soc Enol Viticulture.
  5. ^ CBS News: Jury Gives Popcorn Worker $20M: Missouri Man Says Butter Flavor Vapor Ruined His Lungs
  6. ^ International Flavors and Fragrances SEC Annual Report Form 10K: Item 1: Legal Proceedings. Filed August 5, 2005.
  7. ^ UFCW and Teamsters Petition to OSHA
  8. ^ Scientists Letter to Secretary Chao
  9. ^ Flavoring-Factory Illnesses Raise Inquiries, New York Times, May 6, 2007
  10. ^ SB 456 Senate Bill - Bill Analysis
  11. ^ AB 514 Assembly Bill - Bill Analysis
  12. ^, Doctor warns consumers of popcorn fumes
  13. ^ David Michaels. Popcorn Lung Coming to Your Kitchen? The FDA Doesn’t Want to Know
  14. ^ Reuters New Report: FDA to probe popcorn link in man's lung disease.
  15. ^ Reuters New Report: FDA to probe popcorn link in man's lung disease.
  16. ^ Weaver Popcorn Company. Press Release: Pop Weaver introduces first microwave popcorn with flavoring containing no diacetyl.
  17. ^ Reuters News ReportConAgra to drop popcorn chemical linked to lung ailment
  18. ^
  19. ^ Reuters News Report Reuters- FDA to probe popcorn link in man's lung disease
  20. ^ - EU Commission and Diketones
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Diacetyl". A list of authors is available in Wikipedia.
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