Over thousands of years, Indigenous peoples transformed it from a weedy plant into a crop that stores enormous amounts of starch in potato-like tubers, grows in the poor soils of Amazonia, and is virtually impervious to pests.
Cassava’s many assets seem to make it an ideal product. But there’s a problem: Cassava is highly toxic.
How can cassava be so toxic and yet dominate diets in the Amazon? It all depends on the creativity of the locals. For the past 10 years, my colleague César Peña and I have been studying cassava gardens along the Amazon River and its numerous tributaries in Peru. We discovered numerous varieties of cassava, growers using advanced cultivation strategies to manage cassava toxicity, and elaborate methods to process their hazardous but nutritious product.
The long history of plant domestication
One of the biggest challenges faced by early humans was finding enough food. Our ancient ancestors relied on hunting and gathering, poaching and collecting edible plants at every opportunity. They were surprisingly good at it. So well that their population has rapidly increased from Africa, the birthplace of humanity 60,000 years ago.
Still, there was room for improvement. Foraging for food in the field burns calories from the very resource sought. This paradox forced hunter-gatherers to make a choice: burn calories while searching for food, or preserve calories by staying home. This compromise was almost insurmountable, but people found a way.
Just over 10,000 years ago, they broke the barrier with one of the most transformative innovations in history: the domestication of plants and animals. People discovered that when plants and animals were domesticated, they no longer needed to be chased. And these can be selectively bred to produce larger fruits, seeds and bulkier muscles to eat.
Cassava was the champion domesticated plant of the neotropics. After its initial domestication, it spread throughout the region, reaching areas as far north as Panama within a few thousand years. Growing cassava did not completely eliminate people’s need to search the forest for food, but it eased the burden and provided an abundant, reliable food source close to home.
Today almost every rural family in the Amazon has a garden. Visit any home and you’ll see cassava roasted over a fire, fried into a chewy flatbread called casabe, fermented into beer called masato, and steamed into soups and stews. But before adopting cassava in these roles, people had to figure out how to deal with its toxicity.
Processing a poisonous plant
Pest resistance, one of cassava’s most important strengths, is provided by a strong defense system. The system is based on two chemicals produced by the plant, linamarin and linamarase.
These defensive chemicals are found in cells in the leaves, stems and tubers of the cassava plant, which are usually idle. But when the cells of cassava are damaged, for example by chewing or crushing, linamarin and linamarase react, causing an explosion of harmful chemicals.
One of these is famous: cyanide gas. The explosion also contained other nasty substances, including compounds called nitriles and cyanohydrins. Large doses of these are lethal, and chronic exposures permanently damage the nervous system. These poisons deter herbivores so much that cassava is virtually pest-proof.
No one knows how humans first solved the problem, but ancient Amazonians devised a complex, multi-step detoxification process that transformed cassava from inedible to delicious.
It begins by grinding the starchy roots of cassava on chopping boards decorated with fish teeth, rocks, or nowadays often a rough sheet of tin. Crushing mimics chewing by pests, causing the release of cyanide and cyanohydrins from the root. However, they are dragged into the air, not into the lungs and stomach as when eaten.
The chopped cassava is then placed in rinsing baskets, where it is rinsed, squeezed by hand, and drained repeatedly. The movement of water releases more cyanide, nitrile and cyanohydrin, and squeezing rinses them away.
Finally, the resulting pulp can be further detoxified by drying or baking to complete the process using heat. These steps are so effective that they are still used on Amazon today, even though thousands of years have passed since they were first designed.
A powerful product is poised to roll out
The Amazonians’ traditional methods of grinding, rinsing and cooking are a sophisticated and effective way to turn a poisonous plant into food. But Amazonians took their efforts even further, turning it into a truly domesticated crop. In addition to inventing new methods for processing cassava, they began pursuing and selectively breeding varieties with desirable characteristics, gradually creating a suite of species used for different purposes.
In our travels we have found over 70 different varieties of cassava that are extremely diverse physically and nutritionally. These include a variety of species that range in toxicity, some requiring laborious chopping and rinsing, others that can be cooked as is, but none of which can be eaten raw. There are also species with different tuber sizes, growth rates, starch production and drought tolerance.
Their diversity is valued and they are often given fanciful names. Just as American supermarkets stock apples called Fuji, Golden Delicious and Granny Smith, Amazon orchards stock cassava of bufeo (dolphin), arpón (harpoon), motelo (turtle) and many other varieties. This creative breeding secured cassava’s place in Amazonian cultures and diets, ensuring its manageability and usefulness; just as the domestication of corn, rice, and wheat cemented their place in cultures elsewhere.
Although cassava has been native to South and Central America for thousands of years, its story is not over yet. In an age of climate change and increasing efforts towards sustainability, cassava is emerging as a possible world crop. Its hardiness and flexibility make it easy to grow in variable environments, even if soils are poor, and its natural pest resistance reduces the need to protect it with industrial pesticides. In addition, although Amazon’s traditional methods for detoxifying cassava can be slow, they are easy to replicate and accelerate with modern machinery.
Moreover, Amazon growers choose to preserve various cassava species, making the Amazon a natural repository for genetic diversity. In modern hands, they can be bred to produce new species suitable for purposes beyond Amazonia. These advantages encouraged the first exports of cassava beyond South America in the 1500s, and the range quickly spread into tropical Africa and Asia. Today, production in countries such as Nigeria and Thailand far exceeds that in Brazil, South America’s largest producer. These achievements increase optimism that cassava can be an environmentally friendly source of nutrition for populations worldwide.
While cassava isn’t a familiar name in the U.S. yet, it appears to be on the way. It has long flown under the radar in the form of tapioca, the cassava starch used in pudding and boba tea. It also takes its place on the shelves in the snack section in the form of cassava chips and in the baking section with natural gluten-free flour. Raw cassava is also an emerging entity, appearing under the names “yuca” and “manioc” in stores that cater to Latin American, African, and Asian populations.
Follow it a bit and try it. Supermarket cassava is perfectly safe and there are many recipes available. Cassava fritters, cassava fritters, cassava cakes… the possibilities of cassava are almost endless.
This article was co-authored by César Rubén Peña.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and analysis to help you understand our complex world.
Written by Stephen Wooding University of California, Merced.
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Stephen Wooding receives funding from Project Amazonas, a nonprofit organization that supports humanitarian aid and research projects in the Peruvian Amazon.