Ethyl Carbamate - Occurrence in Beverages and Food

Occurrence in Beverages and Food

The discovery of the widespread presence of ethyl carbamate in alcoholic beverages first occurred during the mid-1980s. To raise public awareness of this issue, the U.S. Center for Science in the Public Interest published, in 1987, Tainted Booze: The Consumer's Guide to Urethane in Alcoholic Beverages. Studies have shown that most, if not all, yeast-fermented alcoholic beverages contain traces of ethyl carbamate (15 ppb to 12 ppm). Other foods and beverages prepared by means of fermentation also contain ethyl carbamate. For example, bread has been found to contain 2 ppb; as much as 20 ppb has been found in some samples of soy sauce. Amounts of both ethyl carbamate and methyl carbamate have also been found in wines, sake, beer, brandy, whiskey and other fermented alcoholic beverages.

It has been shown that ethyl carbamate forms from the reaction of alcohol (ethanol) with urea:

This reaction occurs much faster at higher temperatures, and therefore higher concentrations of ethyl carbamate are found in beverages that are heated during processing, such as brandy, whiskey, and other distilled beverages. Additionally, heating after bottling either during shipping or in preparation will cause ethyl carbamate levels to rise further.

The urea in wines results from the metabolism of arginine or citrulline by yeast or other organisms. The urea waste product is initially metabolised inside the yeast cell until it builds up to a certain level. At that point, it is excreted externally where it is able to react with the alcohol to create ethyl carbamate.

In 1988, wine and other alcoholic beverage manufacturers in the United States agreed to control the level of ethyl carbamate in wine to less than 15 ppb, and in stronger alcoholic drinks to less than 125 ppb.

Although the urea cannot be eliminated, it can be minimized by controlling the fertilization of grape vines, minimizing their heat exposure, using self-cloning yeast and other actions. Furthermore, some strains of yeast have been developed to help reduce ethyl carbamate during commercial production of alcoholic beverages.

Another important mechanism for ethyl carbamate formation in alcoholic beverages is the reaction from cyanide as precursor, which causes comparably high levels in spirits derived from cyanogenic plants (i.e. predominantly stone-fruit spirits and cachaca).