Levels and management of glycosidic nitrile production in North American grown barley varieties

Abstract

Glycosidic nitrile (GN) from malted barley has been identified as the primary precursor of ethyl carbamate (urethane) in new-make whiskey. A specific GN, epiheterodendrin (EPH), is responsible. EPH is a type of cyanogenic glycoside, forming toxic hydrogen cyanide in the pathway leading to ethyl carbamate (EC). The presence of EC, a known carcinogen in many fermented foods, is regulated to varying degrees. For whiskey, the Canadian government has mandated a 150 ppb limit, while the US has a voluntary limit of 125 ppb. In Europe, standards call for newly released distilling barleys to be of the non-GN type. North American breeders are just beginning to select for non-GN and options are likely a decade away. This work considers GN levels of common North American varieties and evaluates malting regime variations, including steep out moisture (40 percent and 45 percent), length of germination (two, four, and six days), and temperature (14 °C, 15 °C and 16 °C) to determine impacts on GN. General standards hold that low producers fall under 0.5 g/tonne GN while high producers sit over 1.5 g/tonne. Varieties tested here averaged 0.20 – 1.52 g/tonne across treatments. As expected, management to minimize acrospire growth mitigated GN while all three process variations had significant impacts: ranges being 0.70 – 1.38 g/tonne (germination time), 0.83 – 1.09 g/tonne (temperature) and 0.56 – 0.96 g/tonne (steep out moisture). While this work does not provide a long-term solution, management is a tool while breeding programs develop North Americana non-GN varieties.