Cassava or manioc (Manihot esculenta, Euphorbiaceae) is the world’s easiest crop to grow. Simply cut the leggy branches into 30 cm sticks and plant them in the soil. The tuberous roots can be harvested after 9-18 months. Cassava chips are similar in taste to potato chips.
This is how we make cassava chips at Dokmai Garden: Peel and wash the tubers to remove the bulk cyanide. Slice the tubers as thin as you can and then throw the slices into a wok with hot soybean oil. After being fried until yellow transfer them to a piece of cardboard to remove excess oil and add salt.
This is a nice tropical snack straight from your monsoon garden. Enjoy the chips with a cold beer and a good friend.
Since cassava can survive dry conditions, it grows very well here in Chiang Mai and in Esan, making Thailand a major exporter of cassava. Hundreds of millions of tonnes/year are produced worldwide as pig feed or tapioca.
The word ‘cassava’ comes from the West Indian Taino language. ‘Manioc’ is derived from the Tupi language of coastal Brazil.
The plant is protected from hungry animals by the compound linamarin, which looks like a glucose sugar with a cyanide ion attached. Linamarin can release cyanide gas when digested. Cyanide chokes cells by inhibiting the mitochondrial enzyme cytochrome c oxidase. Although there are 99 species of the genus Manihot, all native to tropical and warm America, Manihot esculenta is the most important species for cooking. Like in the species ‘apple’ there are many different cultivars of cassava. The ‘sweet’ (non bitter) ones contain lower concentrations of linamarin, and this linamarin is mostly located to the peel.
Are the chips safe to eat in spite of the cyanide? The NSW Food Authority in Australia recommends consumers not to eat more than 100 g of cassava chips a day. Since levels of cyanide vary a lot due to cultivar (15-400 mg HCN/kg fresh cassava), the limit is set to make sure that even if you eat the most cyanide rich chips you would still be OK. Some ‘sweet’ cassava may only contain 2% of the cyanide content in bitter strains.
A risk assessment has been made by Food standards Australia New Zealand (2008): “Two hundred grams of cassava chips is considered to be a reasonable and possible dietary intake for a 20 kg child in a two hour eating session. Hence 200 g of chips eaten by a 20 kg child equates to 160 mg (8 mg/kg bw) linamarin (or 0.15 mg/kg bw available HCN)”. The deadly dose is 60 times higher (9 mg HCN/kg body weight), i.e. it would be dangerous if the child manages to swallow 12 kg (120 bags) in two hours.
Cyanogenic glycosides can be found in marzipan, bamboo shoots and cherries too. Variation in food ingredients is a recipe for joy and health.
Text: Eric Danell
Photo: Eric Danell & Anna Kiss