ETHYL CARBAMATE FORMATION IN GRAIN-BASED SPIRITS: PART III. THE PRIMARY SOURCE

Abstract

Low concentrations of ethyl carbamate, which may occur in distilled spirits are shown to originate from traces of cyanide, produced in distillates by thermal decomposition of the cyanohydrin of isobutyraldehyde (IBAC) which is present in fermented wash. This compound arises during fermentation by the hydrolytic action of yeast beta-glucosidase on a naturally-occurring cyanogenic glycoside, identified as epiheterodendrin (EPH). EPH, which is a heat-stable precursor of IBAC is located in the acrospires of malted barley and is readily transferred to worts during mashing. Although many barley varieties display the ability to produce volatile cyanide, some low-yielders have been identified. EPH is absent from unmalted barley and its development is strongly influenced by malting conditions. Conversion of measurable cyanide (MC) into ethyl carbamate takes place during- or after distillation but, apparently, not before.