Reader question… “A neighbor told me this morning that I shouldn’t be using my crockpot to cook dried beans. She says anything cooked in a crockpot doesn’t get hot enough to get rid of the natural toxins in the beans but I keep seeing recipes for cooking beans in a crockpot. Have you heard of this?” –Audrey J.

Your neighbor is talking about a toxin called phytohaemagglutinin, also known as kidney bean lectin, that is found in many types of beans. Kidney beans contain especially large amounts of this toxin, and amazingly, eating just four or five raw or improperly cooked kidney beans can make a person extremely ill. Ingesting larger amounts can actually cause death. Other beans, including white kidney beans, broad beans and lima beans, contain the same toxin in smaller but still dangerous amounts.

Raw beans naturally contain dangerous levels of this toxin, but when beans are cooked in a crockpot at the usual slow-cooking temperature, the level of toxin in the beans will actually INCREASE. Your neighbor is correct… many dried beans, including kidney beans, should never be cooked solely in a crockpot or slow cooker because they will never reach a high enough temperature for a long enough period of time to destroy enough of the phytohaemagglutinin to make the beans safe to eat. It is also not safe to eat these beans raw or sprouted or ground into flour because of the high levels of toxin.

A patch of ostrich ferns (Matteuccia struthiopteris) agrees: “Cooking red kidney beans in crock pots or slow cookers may not heat them enough to destroy the toxin and may actually potentiate it. Heating to a temperature of 176 degrees Fahrenheit may increase the toxin levels by as much as five times. Crock pots often don’t reach temperatures greater than 167. Using dry heat to cook the beans does not appear to inactivate the toxin. In reported cases, 100 percent of people who ate the beans developed symptoms; age and sex don’t appear to affect the symptoms, which vary in intensity according to how many beans were ingested, according to the FDA.”

So are beans cooked in a crockpot or slow cooker safe to eat? Yes… if the beans are properly soaked and cooked. The university extension services recommend the following steps to destroy these toxins and make the slow cooking process safe.

  1. Soak the dried beans in water for at least five hours (some recommend soaking the beans for at least twelve hours)
  2. Discard the soaking water which will contain leached out toxins
  3. Rinse the beans and cover them with fresh water
  4. Boil the beans (rapid boil) for at least ten minutes
  5. It is then safe to add the beans to the slow cooker and proceed with the recipe