Simple wetting method to remove cyanide from flour

Mixing cassava flour samples with water and standing at 30°C for 5 hours, gives a 3-6 fold reduction in cyanide content (Bradbury, 2006; Cumbana et al., 2007). Water rapidly swells the flour and allows contact between the cyanide containing compound linamarin and the enzyme linamarase that catalyses the breakdown of linamarin to acetone cyanohydrin, which then breaks down spontaneously to give hydrogen cyanide gas. Experiments show that the amount of hydrogen cyanide lost from the flour increases as the amount of linamarase is increased. The method is a gift from God.

The simple method field tested in Mozambique is as follows:

A bowl is filled with cassava flour and a mark made on the inside of the bowl. Water is added with mixing until the wet flour comes up to the same mark. The wet flour is spread in a thin layer not more than the depth of a fingernail on a basket and left in the shade for 5 hours for hydrogen cyanide gas to escape. The same day the wet flour is mixed with boiling water as is the custom, to produce a stiff porridge.

During the field testing in northern Mozambique in 2005, local volunteers were asked to compare stiff porridge made from untreated cassava flour and that made from flour that had been treated. It was found that 60% of the volunteers preferred the taste of stiff porridge made from treated flour, probably because the wetting process removed the bitter-tasting linamarin. The rural women readily accepted this very simple wetting method, which does not require additional equipment, use more water or cause additional work (Muquingue et al., 2005, CCDN News 6, P 3-4, Bradbury, 2007; Bradbury, 2008).

In 2006 Dr Dulce Nhassico of the Faculty of Medicine at Eduardo Mondlane University in Maputo, organised two Workshops for nutritionists and health workers in Nampula City and Quelimane in Mozambique. Mr Arnaldo Cumbana, a chemist at the Provincial Health Laboratory in Beira, who was involved in developing the wetting method (Cumbana et al., 2007), explained the method and the reduction in cyanide content of the flour. A poster was prepared in Portuguese that describes the wetting method. This poster has been modified, translated into many languages and is available for free as a laminated poster (see Posters on cyanide poisoning, konzo and wetting method).