Diacetyl

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 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.

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.

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 microwave popcorn or butter salt), 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. On July 19, 2005, jurors awarded $2.7 million to another popcorn plant worker in Missouri for his claim of diacetyl-induced respiratory problems.

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. The petition was followed by a letter of support signed by more than thirty prominent scientists. The matter is under consideration.

There are currently two bills in the California Legislature to ban the use of diacetyl.

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.

At least one heavy popcorn consumer has been diagnosed with the same disease affecting workers exposed to the substance, bronchiolitis obliterans.

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. Weaver makes the Trail's End brand of popcorn sold by the Boy Scouts of America. ConAgra promises to do the same in a year.

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."

Engineering Controls
Engineering controls are the primary methods for minimizing exposure associated with the use or manufacture of potentially hazardous flavorings. Examples include closed production systems (e.g., to eliminate handling open containers of flavorings or their chemical ingredients for placement into mixing tanks), adequate ventilation, and isolation. Whenever possible, use closed processes to transfer flavorings or their chemical ingredients.


 * Isolate the mixing room and other areas where flavorings and their ingredients are openly handled.
 * Maintain these work areas under negative air pressure relative to the rest of the plant.
 * Use local exhaust ventilation of tanks and other sources of potential exposure (e.g., places where flavorings are openly weighed or measured) as well as general dilution ventilation of the work area to eliminate or reduce possible worker exposures.
 * Obtain information about the design of appropriate ventilation systems from a qualified ventilation engineer or from Industrial Ventilation—A Manual of Recommended Practice [ACGIH 2001].
 * Check ventilation equipment regularly for adequate performance, especially in areas where flavorings and their ingredients are handled (e.g., mixing room) and in adjacent work areas. Also perform checks whenever a process change is made or a problem is suspected.

For processes involving heating of flavorings, keep the temperature as low as possible to minimize emissions of volatile chemicals into the air.

Administrative Controls
Establish and enforce work practices to limit release of chemicals and dust into the workplace air when flavorings or their ingredients are handled.


 * Tightly seal containers with unused or residual amounts of flavorings or their ingredients.
 * Maintain good general housekeeping in any areas where flavorings or their ingredients are handled.
 * Establish standard procedures for cleaning the workplace, tanks and other containers, and spills.
 * Do not use compressed air for cleaning powdered flavorings or ingredients, as this will increase concentrations of airborne particulate.
 * Clean up spills of flavorings or their ingredients promptly using procedures and appropriate protective equipment designed to limit exposure.

Use special caution when removing residual chemicals from tanks and other containers with steam or hot water, as this may increase exposure to volatile chemical vapors.

Restrict access to all areas where flavorings are openly handled; only essential workers should enter these areas and only when properly protected (see section on personal protective equipment).

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.

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