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Structural formula
Ball-and-stick model
IUPAC name
Other names
Dimethyl diketone
431-03-8 YesY
ChEBI CHEBI:16583 YesY
ChEMBL ChEMBL365809 YesY
ChemSpider 630 YesY
Jmol-3D images Image
KEGG C00741 YesY
PubChem 650
Molar mass 86.09 g·mol−1
Appearance Yellowish green liquid
Density 0.990 g/mL at 15 °C
Melting point −2 to −4 °C (28 to 25 °F; 271 to 269 K)
Boiling point 88 °C (190 °F; 361 K)
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 is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY verify (what isYesY/N?)
Infobox references

Diacetyl (IUPAC systematic name: butanedione or butane-2,3-dione) is an organic compound with the chemical formula (CH3CO)2. It is a volatile, yellow/green liquid with an intensely buttery flavor. It is a vicinal diketone (two C=O groups, side-by-side) with the molecular formula C4H6O2. Diacetyl occurs naturally in alcoholic beverages and is added to some foods to impart its buttery flavor.

Chemical structure[edit]

A distinctive feature of diacetyl (and other 1,2-diketones) is the long C-C bond linking the carbonyl centers. This bond distance is about 1.54 Å, compared to 1.45 Å for the corresponding C-C bond in 1,3-butadiene. The elongation is attributed to repulsion between the polarized carbonyl carbon centers.[2]


Diacetyl arises naturally as a byproduct of fermentation. In some fermentative bacteria, it is formed via the thiamine pyrophosphate-mediated condensation of pyruvate and acetyl CoA.[3] Sour (cultured) cream, cultured buttermilk, and cultured butter are produced by inoculating pasteurized cream or milk with a lactic starter culture, churning (agitating) and holding the milk until a desired pH drop (or increase in acidity) is attained. Cultured cream, cultured butter, and cultured buttermilk owe their tart flavour to lactic acid bacteria and their buttery aroma and taste to diacetyl.[4]


Diacetyl is produced industrially by dehydrogenation of 2,3-butanediol. Acetoin is an intermediate.[5]


In food products[edit]

Diacetyl and acetoin are two compounds that give butter its characteristic taste. Because of this, manufacturers of artificial butter flavoring, margarines or similar oil-based products typically add diacetyl and acetoin (along with beta carotene for the yellow color) to make the final product butter-flavored, because it would otherwise be relatively tasteless.[6]

In alcoholic beverages[edit]

At low levels, diacetyl contributes a slipperiness to the feel of the alcoholic beverage in the mouth. As levels increase, it imparts a buttery or butterscotch flavor.

In some styles of beer (e.g. in most beers produced in the British Isles, such as India Pale Ale), the presence of diacetyl can be acceptable or desirable at low or, in some cases, moderate levels. In other styles, its presence is considered a flaw or undesirable.[7]

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

Beer sometimes undergoes a "diacetyl rest", in which its temperature is raised 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 flavor it imparts.[8] It is present in many California chardonnays known as "butter bombs", although there is a growing trend back toward the more traditional French styles.

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.[9][10]


1-Hexanol and diacetyl are strong inhibitors of the CO2-sensitive neurons in the Drosophila melanogaster fruit fly and the Culex mosquito, a vector of several deadly diseases.[11] Fruit flies tend to avoid CO2, but exhaled CO2 is the main attractant for the Culex. [12]


Worker Safety[edit]

United States[edit]

The United States National Institute for Occupational Safety and Health has suggested 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, nonsmoking males. As with other end-stage lung diseases, transplantation is currently the most viable treatment option. However, lung transplant rejection is very common and happens to be another setting in which bronchiolitis obliterans is known to occur.

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.

In 2006, the International Brotherhood of Teamsters and the United Food and Commercial Workers petitioned the U.S. OSHA to promulgate an emergency temporary standard to protect workers from the deleterious health effects of inhaling diacetyl vapors.[13] The petition was followed by a letter of support signed by more than 30 prominent scientists.[14] The matter is under consideration. On 21 January 2009, OSHA issued an advance notice of proposed rulemaking for regulating exposure to diacetyl.[15] The notice requests respondents to provide input regarding adverse health effects, methods to evaluate and monitor exposure, the training of workers. That notice also solicited input regarding exposure and health effects of acetoin, acetaldehyde, acetic acid and furfural.[16]

Two bills in the California Legislature seek to ban the use of diacetyl.[17][18][19]

A 2010 U.S. OSHA Safety and Health Information Bulletin and companion Worker Alert recommend employers use safety measures to avoid exposing employees to the potentially deadly effects of butter flavorings and other flavoring substances containing diacetyl or its substitutes.[20]

A preliminary in vitro study, published in 2012, suggests that diacetyl may exacerbate the effects of beta-amyloid aggregation, a process linked to Alzheimer's disease.[21]

Consumer Safety[edit]

In 2007, the Flavor and Extract Manufacturers Association recommended reducing diacetyl in butter flavorings.[22] Manufacturers of butter flavored popcorn including Pop Weaver, Trail's End, and ConAgra Foods (maker of Orville Redenbacher's and Act II) began removing diacetyl as an ingredient from their products.[23][24]

In 2012, Wayne Watson, a regular microwavable popcorn consumer for years, was awarded $7.27 million in damages from a federal jury in Denver, which decided his lung disease was caused by the chemicals in microwave popcorn and that the popcorn's manufacturer, Gilster-Mary Lee Corporation, and the grocery store that sold it should have warned him of its dangers.[25][26][27]

European Union Regulation[edit]

The European Commission has declared diacetyl is legal for use as a flavouring substance in all EU states.[28] As a diketone, diacetyl is included in the EU's flavouring classification Flavouring Group Evaluation 11 (FGE.11). A Scientific Panel of the EU Commission evaluated six flavouring substances (not including diacetyl) from FGE.11 in 2004.[29] As part of this study, the panel reviewed available studies on several other flavourings in FEG.11, including diacetyl. Based on the available data, the panel reiterated the finding that there were no safety concerns for diacetyl's use as a flavouring.

In 2007, the European Food Safety Authority (EFSA), the EU's food safety regulatory body, stated its scientific panel on food additives and flavourings (AFC) was evaluating diacetyl along with other flavourings as part of a larger study. "The experts of the EFSA AFC panel and its working group on food additives will look at this issue to see if new scientific evidence is available that may require further actions. If the experts conclude that consumer exposure to diacetyl can reach levels well above those considered as safe and, that a possible health risk for consumers cannot be excluded when inhaling diacetyl, EFSA will give priority to the re-evaluation of this substance and provide detailed scientific advice."[30]

Electronic Cigarettes[edit]

A 2014 publication found that diacetyl was present in many sweet-flavoured electronic cigarette liquids. According to that research, diacetyl is approved for food use, but is associated with respiratory disease when inhaled. The study concluded that diacetyl is an avoidable risk for electronic cigarette liquid, and measures could be taken by the industry to eliminate its usage, without limiting availability of flavors. [31]

See also[edit]


  1. ^ Merck Index, 11th Edition, 2946.
  2. ^ K. Eriks , T. D. Hayden , S. Hsi Yang , I. Y. Chan (1983). "Crystal and molecular structure of biacetyl (2,3-butanedione), (H3CCO)2, at -12 and -100 °C". J. Am. Chem. Soc. 105 (12): 3940–3942. doi:10.1021/ja00350a032. 
  3. ^ Speckman, R. A.; Collins, E.B. (1968). "Diacetyl biosynthesis in Streptococcus diacetilactis and Leuconostoc citrovorum". J. Bacteriol. 95 (1): 174–80. PMC 251989. PMID 5636815. 
  4. ^ James M.Jay. Modern Food Microbiology (6th ed.). p. 120. 
  5. ^ Siegel, H.; Eggersdorfer, M. (2005), "Ketones", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a15_077 
  6. ^ Pavia et al. Introduction to Organic Laboratory Techniques (4th ed.). ISBN 978-0-495-28069-9. 
  7. ^ Beer Judge Certification Program style guidelines
  8. ^ "Diacetyl". E.coli Metabolome Database. ECMDB. Retrieved 20 October 2013. 
  9. ^ Nielsen JC, Richelieu M (February 1999). "Control of flavor development in wine during and after malolactic fermentation by Oenococcus oeni". Appl. Environ. Microbiol. 65 (2): 740–5. PMC 91089. PMID 9925610. 
  10. ^ Martineau B, Henick-Kling T, Acree T (1995). "Reassessment of the Influence of Malolactic Fermentation on the Concentration of Diacetyl in Wines". Am Soc Enol Vitic 46 (3): 385–8. 
  11. ^ Discovery Of Natural Odors Could Help Develop Mosquito Repellents
  12. ^ Turner et al. (2011). "Ultra-prolonged activation of CO2-sensing neurons disorients mosquitoes". Nature 474: 87–91. doi:10.1038/nature10081. 
  13. ^ UFCW and Teamsters Petition to OSHA
  14. ^ Scientists Letter to Secretary Chao
  15. ^ Federal Register, 21 January 2009 issue
  16. ^ "OSHA begins rule on diacetyl". Chemical & Engineering News 87 (4): 24. January 26, 2009. 
  17. ^ Flavoring-Factory Illnesses Raise Inquiries, New York Times, May 6, 2007
  18. ^ SB 456 Senate Bill - Bill Analysis
  19. ^ AB 514 Assembly Bill - Bill Analysis
  20. ^ OSHA Recommends Safety Measures to Protect Workers from Diacetyl Exposure, EHS Today, December 10, 2010
  21. ^ More, Swati S.; Vartak, Ashish P.; Vince, Robert (2012). "The Butter Flavorant, Diacetyl, Exacerbates β-Amyloid Cytotoxicity". Chemical Research in Toxicology: 120706140246003. doi:10.1021/tx3001016. 
  22. ^ Comments of the Flavor and Extract Manufacturers Association of the United States on New Information on Butter Flavored Microwave Popcorn, FEMA press release
  23. ^ Weaver Popcorn Company. Press Release: Pop Weaver introduces first microwave popcorn with flavoring containing no diacetyl[dead link]
  24. ^ ConAgra Foods Press Release ConAgra Foods press release announcing removal of added diacetyl
  25. ^ ABC News: 'Popcorn Lung' Lawsuit Nets $7.2M Award
  26. ^ NewsFeed Researcher: 'Popcorn Lung' Lawsuit Nets $7.2M Award
  27. ^ Mark Jaffe (September 21, 2012). "Centennial man with "popcorn lung" disease gets $7.3 million award". The Denver Post. Archived from the original on September 22, 2012. Retrieved September 22, 2012. 
  28. ^ http://www.fsai.ie/legislation/food/eu_docs/Flavourings/Dir99.217.pdf[dead link]
  29. ^ "Opinion of the Scientific Panel on Food Additives, Flavourings, Processing Aids and Materials in contact with Food (AFC) on a request from the Commission". The EFSA Journal 166: 1–44. 2004. 
  30. ^ Europe takes 'wait-and-see' stance on diacetyl flavouring. Oct 2007
  31. ^ Farsalinos, Konstantinos (1 September 2014). "Evaluation of electronic cigarette liquids and aerosol for the presence of selected inhalation toxins". Nicotine Tob Res. online. doi:10.1093/ntr/ntu176. Retrieved 12 September 2014. 

External links[edit]