Effects of processing of grated cassava roots by the 'screw press' and by traditional fermentation methods on the cyanide content of gari

The extent of the loss of hydrocyanic acid (HCN) from grated cassava roots, selected from both the sweet and bitter varieties, was compared in the roasted grit (gari) derived from their fresh pulp which had been dewatered and fermented by two different processes; the quick (1-day) 'screw press' method (QSP) and the slow (3-day) traditional one (STD), respectively. The relative amounts of HCN which had disappeared after 1 day, in the case of QSP, and 3 days, in respect of STD, were comparable (92–100%) for either free (non-glycosidic) or bound (glycosidic) cyanide content of the two cultivars, indicating that the former method was more efficient than the latter in the detoxification of the grated pulp. The QSP method appeared to retain some of the bound cyanide while with the STD method, virtually no bound cyanide was detectable. About 83–91% of the total HCN content of the grated roots was present as free cyanide. It would seem that varietal differences in HCN contents of cassava may not be a critical factor in the preferential selection of the roots for 'garification'.