Glycosidic nitrile and ethyl carbamate in malting barley How serendipity lead to GN0 varieties and an outlook for the barley supply chain Written by Campbell P. Morrissy1,2, Dr. William Thomas3, Dr. Harmonie M. Bettenhausen4, Scott P. Fisk1, and Dr. Patrick M. Hayes1
Glycosidic (sugar) moiety CH3
Malting process
HO
pFriem Family Brewers, Hood River, OR, U.S.
3
James Hutton Institute, Invergowrie, Scotland, U.K.
alt whisk(e)y is a category that is firmly rooted in Scotland but has spread globally and is now being produced by distillers worldwide. The category in the United States is more than three decades old and has recently received a boost with a formal designation from the federal Tax and Trade Bureau currently in review (as of October 2022). Despite being a growing industry there is little domestic barley grown and malted specifically to meet the needs of malt whiskey producers in the United States. As the category grows in North America, there has been an increased interest and focus on glycosidic nitrile (GN) in barley and malt and the resulting ethyl carbamate concentration in final spirit. While other spirits are known to contain ethyl carbamate (EC) — particularly stone fruit brandies — much of the work on the topic has focused on malt whiskey due to global category size. The emphasis in the industry has resulted in breeding efforts that have successfully released barley varieties that are non-producers of glycosidic nitrile
78
CH3
Cyanogenic moiety
N
Epiheterodendrin (EPH), cyanogenic glycoside, defense mechanism for plants
Barley
ß-glucosidase inactive at mashing temps, but new ß-glucosidase is introduced from yeast through arginine (amino acid) metabolism. HO
4 Center for Craft Food and Beverage, Hartwick College, Oneonta, NY, U.S.
M
O
OH OH
1 Department of Crop and Soil Science, Oregon State University, Corvallis, OR, U.S. 2
O
HO
N Isobutyraldehyde cyanohydrin (IBAC)
Fermentation
Heat
N
CH
Hydrogen Cyanide (HC) Distillation H3C
+
OH O
Ethanol and Copper (Cu) react with HC
O
NH2
Ethyl Carbamate (EC), urethane Figure 1. Pathway from epiheterodendrin to ethyl carbamate showing the catalysts involved at each step. Adapted from Bringhurst, 2015 (1). W W W . ARTISANSPIRITMAG . C O M