Production of prussic acid, also known as hydrogen cyanide, occurs naturally in all types of sorghum when the plant tissue is damaged from a freeze or drought. This damage causes dhurrin, a product found in sorghum, to come into contact with enzymes, producing prussic acid.
Although all sorghum types can produce prussic acid, sudan grasses produce the least. Grain sorghum and Johnson grass produce the most. Accumulating almost exclusively in the leaves, new leaf growth can be particularly high in prussic acid. Very little can be found in the stalk and none can be found in the grain.