Beans, Beans: The Potentially Toxic Fruit?
Wait, what?! I’ve lived over 6 decades and never knew what trouble I could get into from not cooking (some) beans properly. I love beans and have probably been lucky in not having a bean-related food poisoning. What clued me in? While researching the Traditional Chinese Medicine thermal properties of foods, I read about sword beans which were previously unknown to me. Apparently, they contain toxic ingredients that are rendered safe when boiled long enough. Was this true of other beans?
Enter the rabbit hole. On further investigation, I discovered that sword beans as well as kidney beans, and less so cannellini beans contain lectins, proteins that make them toxic to bugs and other predators that nibble on them. Sword beans contain not only a lectin, phytohemagglutinin, but also notorious gut irritants called saponins. Kidney beans too have plant-based hemagglutinins as do cannellini beans, although in lesser concentrations. Moreover, raw lima beans and butter beans contain a toxic cyanoglycoside compound, linamarin, which is broken down into cyanide by an enzyme that is released when you chew them.
So how do we manage to eat these beans safely? Most cookbooks recommend the “soak, bring to a boil, then simmer until cooked” regimen that I learned long ago, but it is not enough for the beans mentioned above. Soaking will remove only a bit of these compounds but boiling at 212°F or 100°C for 10 or more minutes will deactivate both the phytohemagglutinins and cyanide-catalyzing enzymes. Simmering (180–190°F) over low heat on the stove or cooking in a crockpot will not achieve this level of heat.
If kidney beans are inadequately cooked, nausea and vomiting, diarrhea, and abdominal discomfort or pain can occur within 3 hours of eating them and last about 4 hours. Many people might attribute this to irritable bowel disease or food poisoning by something else. Indeed, about 20% of all cases of food poisoning involve undercooked kidney beans.
Wow, this was news! People have been eating beans for millennia. There are edible pod beans like green beans (AKA string beans), wax beans, and the wide Italian Romano beans. Shell bean types include kidney, cannellini, garbanzo, pinto, navy, soy, lima, butter, and black beans. There is a spectrum of phytohemagglutinin levels in beans, with red kidney beans having the highest amounts, cannellinis in the middle, and most other shell beans containing much less. There is also a range of sensitivities to these hemagglutinins. I can eat many freshly picked raw green beans from my garden with no ill effects, but my husband tolerates eating only a few without stomach discomfort.
Legumes are an excellent source of protein, fiber, and micronutrients and have health benefits related to blood sugar and cholesterol control. So, what are the ways to make sure that we can eat them without getting sick or uncomfortable? One technique is to sprout them before cooking. Adzuki and mung beans sprout easily and you can cook them once you see the little rootlets appear. Processing soybeans into curds to make tofu or fermenting soybeans to make tempeh also helps with edibility. Boiling pod beans deactivates any phytohemagglutinins; regular green and wax beans should be boiled for about 5 minutes in salted water and the wider Italian green beans require more like 8 minutes to cook. Cooking dried beans thoroughly and discarding both the soaking and cooking water reduces problems with digestion. I used to think that once dried, beans keep forever, but they become hardened with prolonged storage so they take longer both to soften and to deactivate any phytohemagglutinins. In any case, you might consider composting beans that are over a year past their “best used by” date.
Prior to cooking shell beans, you can soak them using the following methods. For quick turnaround, place the beans in a pot, bring them to a boil, turn off the heat, cover, and let them sit for about 2 hours prior to cooking. If planning ahead, place the beans in a container, add 3x the amount of cool water (i.e., 1 cup dried beans to 3 cups water), and soak for about 4 to 8 hours on the counter or overnight in the fridge. Drain and discard the soaking water since it contains irritating saponins and gas-producing alpha-galactosides.
To cook, place the soaked shell beans in a pot, add 3x the amount of water and boil for about 10 to 15 minutes. Then, turn down the heat to simmer the beans until they soften. Depending on the size of the beans and how dried out they are, this can take 1–1/2 hours to 4 hours. Pressure cooking the beans (which takes way less time anyway) is another alternative. Discard the cooking water prior to adding the beans to the final dish.
Some recommend adding salt to the soaking water, but I add salt at the time of simmering. Others add salt after cooking. There are lots of culinary arguments about this.
For many, gastrointestinal distension from bean-related gas production may cause abdominal distress. To reduce gassiness from canned shell beans, I recommend emptying them into a colander and rinsing since this removes some of gas-producing factors (and a bit of the added salt). Eating beans slowly and chewing them thoroughly also helps. Additionally, Beano®, available over the counter, aids in their digestion. Bon appétit!
This article was originally published on the author’s site.
