Cassava and bamboo shoots available in Australia and New Zealand are safe to eat provided you prepare them properly. These foods contain cyanogenic glycosides; chemicals that can be broken down to release hydrogen cyanide, which can be harmful to consumers.
Under the Food Standards Code cassava and bamboo shoots must be labelled with (or if unpackaged accompanied by) a statement indicating they must be fully cooked (and peeled in the case of cassava) before eating.
The simplest method of detoxifying cassava roots is the wetting method1:
- Peel the tubers, chop them and grind them into flour
- Mix the flour with water in a ratio of 1 part cassava flour to 1.25 parts water, by weight
- Spread the mixture of flour and water in a layer not more than 1 cm thick, and stand for 5 hours at 30°C.
Other methods include2:
- Soaking cassava roots for 6 days, then grating them and fermenting the resulting mash for 4 days. This has been shown to remove 98% of cyanogenic glycosides.
- Soaking fresh cassava roots for 3 days followed by 3 days of drying. This removes around 86% of cyanogenic glycosides.
The extent of detoxification of roots by cooking methods such as boiling, steaming, baking or frying varies from 10 to 75%. None of these are reliable to ensure that the cyanogenic glycoside content is decreased to a level that does not pose a risk to human health3.
Cassava leaves are a better source of protein, minerals and vitamins compared to cassava roots however the leaves contain a higher concentrations of cyanogenic glycosides. Simple methods to detoxify cassava leaves, that largely preserve proteins and vitamins, include4:
- Pounding leaves for a minimum of 10 minutes until the leaves are well macerated, followed by washing the leaves in twice their weight of water at ambient temperature This reduces cyanide content by 92%.
- Soaking leaves in 10 times their weight of water at 50°C for two hours, changing the water and soaking the leaves again in in 10 times their weight of water at 50°C for two hours.
Bamboo shoots are an Asian food sourced from the underground stems of the bamboo plant. Of the many bamboo species, only a small number are used as food.
Like cassava, unprocessed fresh bamboo shoots contain cyanogenic glycosides.
To make them safe, slice fresh bamboo shoots in half lengthwise, peel the outer leaves away and trim any fibrous tissue at the base. Then slice them thinly into strips and boil in lightly salted water for eight to ten minutes. Discard the cooking water after use.
Canned or dried bamboo shoots are widely available and are safe because processing reduces hydrogen cyanide to safe levels.
1Bradbury JH and Denton IC (2010) Rapid wetting method to reduce cyanogen content of cassava flour. Food Chemistry 121: 591-594
2Montagnac JA, Davis CR and Tanumihardjo SA (2019). Processing techniqus to reduce toxicity and antinutrients of cassava for use as a staple food. Comprehensive Reviews in Food science and Food Safety 8: 17-27
3Burns AE, Bradbury JH, Cavagnaro TR and Gleadow RM (2012) Total cyanide content of cassava food products in Australia. Journal of Food Composition and Analysis 25: 79-82
4Bradbury JH and Denton IC (2014) Mild methods of processing cassava leaves to remove cyanogens and conserve key ingredients. Food Chemistry 127: 1755-1759