by Judith E. Foulke
The Food and Drug Administration is carefully evaluating studies to determine if there could be a long-term health risk to consumers from urethane in alcoholic beverages.
Urethane is a chemical substance that forms naturally during the fermentation process. It causes cancer in animals, but it is not known if it poses any significant health risk to humans. Based on data currently available, FDA does not believe that urethane levels in alcoholic beverages currently on the market are an immediate short-term health risk.
Until all scientific research is completed and evaluated, and regulations established, FDA is working with industry to reduce any potential risk to humans from urethane and is participating in tests to find out if the small amounts of urethane present in alcoholic beverages might be harmful.
Industry has voluntarily agreed to develop and use manufacturing techniques to reduce urethane's levels as much as possible. The Distilled Spirits Council of the United States (DISCUS), the American Association of Vintners, and the Wine Institute have told FDA they are studying how urethane forms during fermentation and are changing manufacturing processes to control its formation in alcoholic beverages.
FDA and the Bureau of Alcohol, Tobacco and Firearms (ATF) have done limited surveys of the urethane content in alcoholic beverages, and FDA has evaluated existing urethane toxicity data. In addition, at FDA's request, the National Toxicology Program, a federally funded research group, has done an initial study in animals to help FDA determine if urethane in alcohol poses a significant risk to humans.
Follow-up studies are not complete, and for now, according to the Cancer Assessment Committee of FDA's Center for Food Safety and Applied Nutrition, there is not yet enough information to assess the risk.
Urethane by Nature
Urethane formation is not a new phenomenon produced by high-tech processing. The chemical forms naturally in wine during yeast fermentation of fruit juice. Fermentation also produces urea from the yeast metabolism of arginine, an amino acid in grapes. Recent studies show that when urea reacts with ethyl alcohol after fermentation, ethyl carbamate, another name for urethane, results.
Alcoholic beverages other than wine present variations on this process, which complicates studies. Levels of urethane differ with each type of alcoholic beverage, explains Benjamin J. Canas, of FDA's division of food chemistry and technology. For example, heat seems to accelerate the production of urethane. Some sherries are baked to provide a rich taste, and bourbons are distilled at high temperatures. Both processes may raise urethane levels. Also, levels can differ significantly, even among different bottles of the same variety or brand, Canas says. (See "Too Many Drinks Spiked with Urethane" in the April 1988 FDA Consumer.)
In 1985, work done by Health and Welfare Canada, FDA's Canadian counterpart, brought international attention to the issue of urethane in alcoholic beverages. Canadian authorities had detected the chemical in certain wines and distilled spirits, and had set levels for regulatory action.
FDA and ATF sampled the market and found that imported fruit brandies contained the highest levels of urethane--averaging a little less than 1,200 parts per billion (ppb). Sake followed with about 300 ppb, and then bourbon with levels averaging 150 ppb.
Grape table wines had urethane levels averaging 13 ppb, but dessert wines, such as sherries and liqueurs, averaged about 115 ppb.
Industry Efforts
The wine and distilled spirits industries have invested in basic research, plant modifications, and analytical testing to achieve the reductions in urethane levels they've made so far, says Gregory W. Diachenko, Ph.D., chief of FDA's food formulation branch.
The Wine Institute, for example, is encouraging several changes in grape growing and wine production that can lower urethane levels. For example, it is encouraging grape growers to minimize fertilization. Heavily fertilized vineyards tend to produce grapes that contain high levels of arginine, thus leading to higher urea and urethane levels.
The institute also recommends using a type of yeast, known by the French name prise de mousse, for the fermentation process. This yeast produces wine with lower levels of urea. And the institute is asking the industry to fortify (add alcohol to) dessert wines at a specific time during the fermentation process when the urea levels are the lowest. (Fortified wines contain more than 14 percent alcohol and have the most urethane of all wines.)
The wine industry has a monitoring program involving 20 of the largest-volume U.S. wineries and about 60 other wineries. Under this program, the companies annually sample a cross-section of their bottled wines for urethane levels. The wine industry has given FDA yearly summaries of sampling surveys since 1989.
Urethane levels in wines are getting lower, according to FDA supervisory research chemist Frank L. Joe, Ph.D., who has assembled statistics from the summaries. In 1987, a sampling showed table wines averaged 13 ppb, and retail bourbons averaged 150 ppb. In 1991, those numbers had dropped to 10 ppb for domestic table wines and 68 ppb for bourbons (see accompanying article).
The Wine Institute and the American Association of Vintners, representing the U.S. wine industry, voluntarily set a target of 15 ppb for table wines from the 1988 harvest, and 60 ppb for fortified wines from the 1989 harvest. FDA has asked the industry to consider reducing its target levels based on the encouraging results of its urethane-lowering efforts.
The distilled spirits industry is also working toward lowering the urethane levels in its products, says Diachenko. The industry set 125 ppb as its target for urethane levels in all new whiskey produced as of Jan. 1, 1989. It's achieving this target by modifying the distillation processes. For example, DISCUS has recommended that distillers add copper packing to the upper parts of stills to improve the efficiency of the process. It's also improving methods for cleaning stills to cut down on the buildup of urethane or other chemicals that might form, and it's monitoring the operation of the stills so that urethane is not carried by distilled vapors into new batches.
Like the wine industry, DISCUS is monitoring production of all its 17-member bourbon distillers in the United States. Distillers sample daily for urethane in fresh distillate.
DISCUS provides FDA with quarterly reports of weekly averages of urethane levels, with the highest and lowest levels on any day for each week of the quarter. The weekly averages for all distillers have been below their target levels.
The highest average level in the first quarter of 1992 was 109 ppb, Joe reports. Many distillers have achieved weekly averages below 30 to 40 ppb.
ATF does its own sampling as a backup to the data FDA receives from industry. Although industry has been sampling products since 1987, the lower urethane levels may not show up this year in some brands of distilled spirits because distillates are usually aged four to eight years before marketing, says Canas.
Some companies have found that urethane levels in certain bourbon batches may go up slightly over time during the aging process, says Diachenko. Some scientists believe that baked beverages such as sherries stop producing urethane after baking, while wines that have no further processing could continue to produce urethane from the urea that remains after yeast fermentation.
Therefore, FDA asked the wine industry to revise its sampling and analysis protocols to ensure that future data reflect urethane levels found in bottled products purchased by consumers. DISCUS has also asked its members to investigate ways to identify and eliminate any other substances that could be causing the increases in aged products.
Industry studies suggest that if urease, an enzyme capable of reducing urea levels in fermented drinks, is added to products such as dessert wines, which contain high levels of urea, the urethane content could be reduced, Diachenko says. FDA is currently evaluating a petition from industry to permit the use of urease in wine production.
Foreign Exporters
FDA has alerted all countries that export alcoholic beverages to the United States that they need to develop programs to meet the voluntary urethane target levels established by the U.S. industry. Research published in Britain, France, Germany, and Switzerland suggests that these countries are making some progress and that the levels in most imported alcoholic products have come down considerably (see accompanying article).
H. Tanner, Ph.D., from the Swiss Federal Research Institute, recommends that fruit pits, such as cherry and apricot, not be used in the manufacture of fruit brandies. His study shows that when pits are crushed and used in the beverage, reactions involving chemicals naturally in the pits cause more urethane to form. Diachenko says that FDA presently has little data to confirm how effective this and recommendations of other European countries have been in reducing urethane levels in fruit brandy.
FDA will continue to be involved in urethane-related activities with industry, the National Toxicology Program, and ATF. The agency is continually reevaluating its urethane policy as new information becomes available.
Should consumers be worried about urethane in alcoholic beverages? Keeping in mind the recommendation to consume alcohol in moderate amounts, the answer is "no." However, a prudent choice might be to limit consumption of products, such as fruit brandies, that show consistently higher levels of urethane.
Judith E. Foulke is a staff writer for FDA Consumer.
Wine and Whiskey Sampling
FDA and the U.S. Bureau of Alcohol, Tobacco and Firearms has sampled wines and whiskeys from domestic and foreign producers to determine urethane levels.
The following are the results of two samplings measuring average urethane levels in parts per billion (ppb). The 1987 figures represent the FDA-ATF initial survey of domestic and imported alcoholic beverages, collected from January 1986 through August 1987. This compares with an ATF sampling done in 1991 that shows urethane levels decreasing in most instances.
Product Average Urethane Level (ppb)
1987 1991
Domestic Imported
brandy (grape) 40 10 45
brandy (fruit) 1200 5 255
bourbon (retail) 150 70 55
rum 20 2 5
liqueur 100 10 25
scotch 50 * 55
sherry 130 10 40
port 60 23 26
grape wine 13 10 15
sake 300 55 60
* Scotch is not manufactured domestically.
FDA Consumer / January-February, 1993
This FDA Consumer article is mirrored from the FDA Web Site at http://www.fda.gov/bbs/topics/CONSUMER/CON00193.html.
Hypertext by frf on 1998-JAN-29