By Harold McGee
Cyanogens are molecules that warn and poison animals with bitter hydrogen cyanide, a deadly poison of the enzymes that animals use to generate energy. When the plant’s tissue is damaged by chewing, the cyanogens are mixed with the plant enzyme that breaks them apart and releases hydrogen cyanide (HCN). Cyanogen-rich foods, including manioc, bamboo shoots, and tropical varieties of lima beans, are made safe for consumption by open boiling, leaching in water, and fermentation. The seeds of citrus, stone, and pome fruits generate cyanide, and stone-fruit seeds are prized because their cyanogens also produce benzaldehyde, the characteristic odor of almond extract.