Grown as an annual crop, the root is dried and ground into flour, which can be used similarly to wheat (and is so used by some people with allergies to other grain crops). Cassava root is also made into tapioca. The root contains free and bound cyanogenic glucosides[?] which are converted to HCN in the presence of linamarase[?], a naturally occurring enzyme in cassava. In the past, cassava was categorized as either sweet or bitter, signifying the absence or presence of toxic levels of cyanogenic glucosides. Sweet cultivars can produce as little as 20 mg of HCN per kg of fresh roots, while bitter ones may produce more than 50 times as much. Bitter varieties must be processed so as to remove the cyanogenic gluosides.