Ethyl carbamate (urethane, C(2)H(5)OCONH(2)) is a known genotoxic carcinogen of widespread occurrence in fermented food and beverages with highest concentrations found in stone-fruit spirits. Between 1986 and 2004, 631 cherry, plum or mirabelle (yellow plum) spirits were analysed for ethyl carbamate using gas chromatography in combination with mass spectrometry after extrelut extraction. The ethyl carbamate concentration of the samples ranged between 0.01 mg l(-1) and 18 mg l(-1) (mean 1.4 mg l(-1)). After exposure of the samples to UV light, significantly (p=0.001) higher concentrations between 0.01 mg l(-1) and 26 mg l(-1) (mean 2.3 mg l(-1)) were found. The ethyl carbamate concentration increased on average by 1.3 mg l(-1). A linear correlation between the year of sampling and ethyl carbamate concentration showed a statistically significant but very slight decrease (R=-0.10, p=0.024). However, if only samples which officially were non-compliant were considered exceeding the upper limit of 0.4 mg l(-1) more than twice, a significant reduction (R =-0.56, p=0.018) of the quota was evident. This shows that measures to reduce ethyl carbamate were successfully introduced in many distilleries. However, nearly 20 years after the first warnings about ethyl carbamate in spirit drinks, the problem persists especially in products derived from small distilleries. During experimental production of stone-fruit spirits using state-of-the-art technologies, it was shown that the occurrence of ethyl carbamate in stone fruit spirits is preventable. Even for small distilleries, simple possibilities like destoning exist to minimize the ethyl carbamate content.

To evaluate the influence of stone content on spirit quality from stone fruit, cherry and plum mashes were prepared and fermented with a commercial and a diploid laboratory yeast strain. Fermentation parameters such as sugar content and ethanol production were followed. Despite an initial lag phase in cherry spirits, both yeast strains performed similarly, as substantiated by the determination of specific flavor compounds, ethyl carbamate, and methanol in the mashes and after distillation. The spirits produced were subjected to sensory analyses by trained panels of at least 25 judges. Although mashes retaining the stones could be clearly distinguished from those where the stones had been removed, no significant preference could be attributed to either spirit, indicating that qualities added by the presence of stones during fermentation are largely a matter of personal taste. Interestingly, the yeast strain used for fermentation seemed to have little influence on the spirit quality.

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.

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