Cassava is a root vegetable native to the Americas. Cassava (scientific name Manihot esculenta, Crantz) goes by many common names, including yuca or yucca, manioc and Brazilian arrowroot. (Additional Brazilian names include mandioca, aipim or macaxeira).1 Tapioca (in North America) refers to the starch extracted from the cassava root.
The earliest firm evidence for cassava cultivation comes from a Mayan site dating back fourteen hundred years. Brazilians in the Amazon region may have domesticated cassava directly from a wild plant.2 In the sixteenth century, Portuguese traders from Brazil introduced cassava to Africa.
In the present day, cassava is a staple food for over half a billion people worldwide.3 Over ninety countries cultivate cassava, which is the third most common complex carbohydrate consumed (after rice and maize) in Asia, Africa and Central and South America. Nigeria is the world’s largest cassava producer.4 As a crop, cassava is drought-tolerant and can handle acidic soil and the removal of its leaves by pests.
There are both sweet and bitter varieties of cassava, with the sweet varieties more commonly grown for consumption. Both varieties contain antinutrients—the bitter varieties to a far greater extent.3,5 In addition, cassava contains naturally occurring toxins called cyanides or “cyanogenic glucosides” (the plant toxins linamarin and lotaustralin), which concentrate heavily in the peel but also are present in the flesh. Interestingly, cassava grown during times of drought is much more toxic.
A moderate intake of cassava’s cyanide compounds (such as those also found in apple cores and the pits of stone fruits) can produce a headache followed by mild heart palpitations. In the absence of proper preparation techniques (discussed in the next section), a number of more serious health conditions also can result from overconsumption of the cyanide found in cassava.3,6,7,8 These conditions include goiter, pancreatitis and a neurological disorder called ataxia or konzo, which affects the ability to walk. A person who experiences severe cyanide poisoning will exhibit symptoms such as vertigo, vomiting and collapse within four to five hours. The customary treatment is an injection of thiosulfate, which allows the patient’s body to detoxify by converting the poisonous cyanide into thiocyanate.
TRADITIONAL CASSAVA PREPARATION
Fortunately, there are ways to neutralize the cyanide and also reduce cassava’s phytic acid content (see Phytic Acid Content of Cassava, page 82). Notably, the enzyme linamarase is naturally occurring within cassava and “acts on the [cyanide] glucosides when the cells are ruptured.” 9 Many cultures traditionally have soaked their cassava roots in water, grinding them into a paste and spreading the paste out in the sun. Within five hours, the linamarase breaks down almost 85 percent of the cyanide, allowing the cyanogenic glucosides to convert to hydrogen cyanide (HCN), which then evaporates.
Other traditional practices include peeling the root and soaking, boiling, dehydrating and/or fermenting the cassava. Although peeling and thorough cooking generally are sufficient to make the sweet varieties safe for consumption, the bitter varieties require more steps to make them edible, such as squeezing, pressing and fermenting.10
Fufu and gari are examples of traditional foods that safely reduce cyanogenic compounds using fermentation.11 Both are important staples in Africa. Preparation of fufu involves mashing cassava root and allowing the cassava to ferment with Lactobacillus bacteria.12 Gari calls for peeling, grating, draining, pressing and fermenting the cassava pulp, and then amending the result by adding various ingredients such as palm oil, vegetable sauce, sugar, coconut, roasted groundnuts, dry fish or boiled cowpea (a leguminous seed).13
MODERN CASSAVA FLOUR
Grain-free enthusiasts have promoted cassava flour as the “holy grail” of grain-free flours because of its ability to substitute in many recipes for wheat flour.14 Production of cassava flour entails peeling, dehydrating and grinding the whole root. However, the manufacture of a high-quality cassava flour, “while simple in principle…requires great care.”15 This is because cassava presents some unique challenges.
On a small household scale, sun-drying and fermenting cassava is a time-honored traditional practice that has obvious benefits in terms of reducing antinutrient levels. For commercial cassava flours produced on a larger scale, however, fermenting cassava in the sun is difficult to control and can pose several safety risks. First, if the sun is not out or the outside temperature is not high enough and the material does not dry out sufficiently, the cassava flour may retain a moisture content that exceeds safe limits. Microbial growth will thrive in the moisture, increasing the risk of mold and other undesirable microorganisms. When allowed to sit for too long, cassava quickly grows Aspergillus flavus, a mold that produces toxic and carcinogenic aflatoxins.5 It is important, therefore, to promptly harvest and process young cassava roots and pay attention to drying parameters and moisture content. Even with adequate monitoring of moisture content, sun-drying cassava can expose it to inadvertent contamination with unwanted microorganisms or debris that can escape visual inspection. In addition, overly prolonged sun-drying can alter the chemistry of the starches in the flour.
The safest (from a mold standpoint) modern-day alternative to fermenting in the sun is to oven-dry the cassava and minimize storage time after harvesting. Ensuring a short storage time between harvest, followed by thorough washing, peeling and moderate heat application can drastically reduce mold risks. Industrial drying ovens and appropriate drying times can reduce the microbial presence to safe or negligible levels and produce a moisture content that is low enough to prevent further microbial growth after packaging and subsequent storage. Use of proper processing, drying and monitoring techniques also substantially reduces cyanide-based toxins,16 making it possible to produce cassava flour with cyanide levels well under the food industry standard for cassava flour of ten parts per million (ppm).17
BENEFITS OF CONSUMING CASSAVA
Cassava provides complex carbohydrates suitable for many who have trouble digesting other carbohydrates such as rice, quinoa or potatoes. Cassava also contains significant amounts of calcium, phosphorus and vitamin C.18 On the other hand, cassava root does not provide any protein or fat, and populations that are overly reliant on cassava as a primary food staple can end up nutrient-deficient.19 In contrast to the root, cassava’s leaves are high in protein and particularly the amino acid lysine, although they must be well cooked to dissipate the hydrocyanic acid content. A culinary use in Sierra Leone involves extensively pounding and shredding the cassava leaves, rinsing them many times to remove the bitter flavor and using them to cook palaver sauce.20 In locations such as Guyana, a process that involves boiling and then slowly simmering bitter cassava root sap creates a thick, spiced syrup called cassareep; the cooking eliminates the poisonous cyanide compounds.21
Many individuals and researchers are interested in cassava’s resistant starch content.22 Resistant starch is a prebiotic that remains undigested (i.e., “resistant”) in the small intestine and then feeds microflora when it ends up in the colon. Its fermentation in the colon helps to provide a healthy inner ecosystem through the production of a beneficial shortchain fatty acid called butyrate, which induces differentiation of colonic regulatory T-cells.23 T-cells are responsible for creating healthy immune responses and reducing inflammation. With age, humans produce fewer T-cells, making it helpful to take in more prebiotic foods. It is common to observe improvement with issues such as constipation after increasing one’s intake of resistant starch.
Heating and cooling cassava flour or root ensures that the cassava is safe to consume and also catalyzes production of cassava’s resistant starch.24 (The tapioca starch extracted from cassava root does not contain high amounts of resistant starch, however.) All high-quality brands of cassava flour will have already heated and cooled their cassava, which means the resistant starch is already present. Thus, any recipe that uses cassava flour will provide resistant starch.
PHYTIC ACID CONTENT OF CASSAVA
Cassava has a high phytic acid content compared to other roots such as potatoes and sweet potatoes, with phytate levels measured at 0.133 percent of the fresh weight of the cassava root.25 Phytates inhibit the absorption of minerals and other nutrients. Cooking and/or fermenting cassava root reduces its phytate content considerably.26 One study measured the phytate levels in various traditional Ghanaian dishes, including a dish called konkonte prepared from fermented cassava.27 Although phytate levels were high in some of the other dishes, the investigators detected zero phytates in konkonte, attributing this result to the fermentation process. This example provides excellent encouragement that fermenting cassava may not only reduce phytates, but in some instances, eliminate them altogether.
The phytate content of commercial cassava flours varies by brand, depending on the processes used to reduce the antinutrients. In general, fermentation reduces phytates to a greater extent than oven-drying.26 (When baking with oven-dried cassava flours, consumers can further reduce phytates by using the techniques discussed in the Recipes section.)
ON THE HORIZON
Unfortunately, field trials for a genetically modified (GM) cassava have been taking place for over five years28 and may pose a threat to cassava’s genetic heritage. The stated aim of the GM-biofortified cassava is to provide more zinc, iron, protein, vitamin A and vitamin E to undernourished consumers in low-income nations who rely on cassava as a staple, and also to reduce cassava’s levels of toxic cyanogenic glucosides and “delay postharvest deterioration.” 3 The Bill & Melinda Gates Foundation, an aggressive proponent of GM foods, is providing the funding for the not-yet-approved “BioCassava Plus.”29 Industry food scientists also have tried fortifying cassava products with soybeans in an attempt to address cassava’s “macronutrient and micronutrient deficiencies.”30
I have found that it is preferable to ferment cassava flour in the refrigerator rather than at room temperature. The general principle is to combine cultured or soured raw milk with cassava flour into a batter and let the batter sit in the refrigerator for three to five days. The probiotics in the raw milk predigest the antinutrients in the cassava. I use this method weekly with my delicious grain-free sourdough waffle batter, which I store in a mason jar. Once fermented, the batter provides an easy breakfast each morning. For further grain-free recipes incorporating cassava flour (including butternut squash muffins, sandwich bread, coffee cake and pumpkin pancakes), visit my Eat Beautiful blog.31
When buying cassava flour, be sure to obtain it from a company that uses appropriate processes to control temperature, moisture and toxicity (see recipes). With an awareness of proper techniques to eliminate cassava’s naturally occurring cyanide compounds and minimize phytic acid, cassava can become a satisfying addition to a varied, nutrient-dense diet.
SOURDOUGH CASSAVA WAFFLES
Makes 8 waffles.
1 1/4 cups cassava flour
(I recommend Otto’s Naturals brand)
4 eggs, preferably from pastured chickens
1 cup sour or cultured raw milk*
1 cup of a hard, aged cheese (e.g., Parmesan, Romano, Pecorino, Asiago), grated*
1/3 cup animal fat (such as lard, duck fat, butter or ghee), melted and slightly cooled, or avocado oil
1/2 teaspoon baking soda
1/2 teaspoon sea salt
*For a dairy-free alternative that uses sauerkraut juice to ferment the cassava at room temperature, visit my Eat Beautiful blog.32
Whisk together cassava flour, baking soda and sea salt. Puree or whisk together wet ingredients (eggs, sour milk and melted fat). Pour the wet ingredients into the dry and fold together. Add the cheese.
Store batter in the refrigerator in a quart-size mason jar. Store for a minimum of 24 hours to sour the dough and reduce phytic acid. Storing for three to five days will produce a stronger sourdough flavor and greater reduction in antinutrients. Cook in waffle iron, being careful not to overflow the batter.
GRAIN-FREE SOURDOUGH BREAD
Makes one loaf (about 10 slices).
2 cups raw nuts or seeds of choice (soaked for two hours in warm filtered water, then drained and rinsed)
1/2 cup filtered water
1/8 cup sauerkraut liquid
3/4 cup cassava flour (such as Otto’s Naturals brand)
3/4 cup chia seed meal (blend 2 cups chia seeds in a dry, high-powered blender on medium speed for 10 seconds, measure after blending)
1/4 cup tallow or butter (melted and cooled) or avocado oil
2 tablespoons raw honey
1/2 teaspoon sea salt
1/2 teaspoon baking soda
Purée wet nuts or seeds in a high-powered blender with filtered water until smooth (about 50 seconds). Add sauerkraut juice. Purée again until just combined (about 10 seconds). Transfer to a ceramic bowl and cover loosely with a towel or plate. Place in a very warm location (ideally 95 to 105 degrees Fahrenheit) for 12 hours or overnight. A dehydrator or oven with the light on works best, but the countertop will work, too, if your home temperature is 70 degrees Fahrenheit or higher. Fermentation will still occur at 70 degrees but will take about 24 hours.
After soaking for 12 to 24 hours, preheat oven to 325 degrees Fahrenheit.
Grease a loaf pan. Sift together cassava flour, chia seed meal, baking soda and sea salt. Set aside.
Place eggs, fat of choice (tallow, butter, avocado oil or other high-quality fat), and honey into a stand mixer or food processor and mix on medium speed until completely blended (about 30 seconds). Add nuts or seeds and cassava flour mixture. Mix with the paddle attachment until thoroughly combined, but not over-mixed. Pour into the greased loaf pan. Bake until a sharp knife inserted into the center comes out clean (about 50 to 55 minutes). Cool completely before removing from the pan and slicing.
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13. Integrated Cassava Project. Gari. http://cassavabiz.org/postharvest/Gari01.htm.
14. Bryan L. 5 things you need to know about cassava flour. Downshiftology, July 7, 2017. https://downshiftology.com/5-things-you-need-to-know-about-cassava-flour/.
15. Food and Agriculture Organization (FAO). Cassava flour and starch: importance of quick processing. http://www.fao.org/docrep/X5032E/x5032E02.htm.
16. Otto’s Naturals. FAQs. http://www.ottosnaturals.com/faq/.
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19. Gegios A, Amthor R, Maziya-Dixon B, et al. Children consuming cassava as a staple food are at risk for inadequate zinc, iron, and vitamin A intake. Plant Foods Hum Nutr 2010;65(1): 64-70.
20. Eat Your World. Leaf stews/plasas. http://eatyourworld.com/destinations/africa/general_sierra_leone/sierra_leone/what_to_eat/leaf_stews_plasas.
21. Nelson C. What is cassareep? How to make cassareep for Guyanese pepperpot. The Spruce, April 4, 2017. https://www.thespruce.com/what-is-cassareep-2138254.
22. Ogbo FC, Okafor EN. The resistant starch content of some cassava based Nigerian foods. Nigerian Food Journal 2015;33(1): 29-34.
23. Furusawa Y, Obata Y, Fukuda S, et al. Commensal microbe-derived butyrate induces the differentiation of colonic regulatory T cells. Nature 2013;504: 446-450.
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25. Phillippy BQ, Bland JM, Evens TJ. Ion chromatography of phytate in roots and tubers. J Agric Food Chem 2003;51(2): 350-353.
26. Food and Agriculture Organization. Phytate. http://www.fao.org/docrep/t0207e/T0207E09.htm.
27. Annor GA, Debrah KT, Essen A. Mineral and phytate contents of some prepared popular Ghanaian foods. Springerplus 2016;5: 581.
28. Donald Danforth Plant Science Center. BioCassava Plus. https://www.danforthcenter.org/scientists-research/research-institutes/institute-for-international-crop-improvement/crop-improvement-projects/biocassava-plus.
29. Nayar A. Grants aim to fight malnutrition. Nature, April 14, 2011. https://www.nature.com/news/2011/110414/full/news.2011.233.html.
30. Kolapo AL, Sanni MO. A comparative evaluation of the macronutrient and micronutrient profiles of soybeanfortified gari and tapioca. Food Nutr Bull 2009;30(1): 90-94.
32. Stevens M. Cassava flour sourdough waffles. http://eatbeautiful.net/2017/07/09/cassava-flour-sourdough-waffles-grain-free-reduce-phytic-acid-increase-nutrition-sourdough-learn-make-grain-freepaleo-sourdough-recipes/.
This article appeared in Wise Traditions in Food, Farming and the Healing Arts, the quarterly magazine of the Weston A. Price Foundation, Winter 2017.