Contribution of the fermenting yeast strain to ethyl carbamate generation in stone fruit spirits

Fermented fruit and beverages frequently contain ethyl carbamate (EC), a potentially carcinogenic compound that can be formed by the reaction of urea with ethanol. Both are produced by the yeast Saccharomyces cerevisiae with ethanol as the major end product of hexose fermentation and urea as a by-product in arginine catabolism. In spirit production, EC can also be derived from cyanide introduced by stone fruit. To determine the relative contribution of yeast metabolism to EC production, we genetically engineered a diploid laboratory strain to reduce the arginase activity, thus blocking the pathway to urea production. For this purpose, strains with either a heterozygous CAR1/car1 deletion or a homozygous defect (car1/car1) were constructed. These strains were compared to the parental wild type and to an industrial yeast strain in cherry mash fermentations and spirit production. The strain with the homozygous car1 deletion showed a significant reduction of EC in the final spirits in comparison to the non-engineered controls. Nevertheless, using this strain for fermentation of stoneless cherry mashes did not completely impede EC formation. This indicates another, as yet unidentified, source for this compound.