Cooking your own beans is a great way to save money, reduce waste and lower your sodium consumption, but eating improperly cooked beans can lead to serious illness. This is especially true for kidney beans.

Eating raw or undercooked kidney beans can lead to food poisoning, including symptoms such as nausea, vomiting and diarrhea. Only a few beans are needed to cause poisoning.

Kidney beans, or red beans, contain a natural protein, Lectin, that is found in many plants, animals and humans. However, at high levels, like that found in raw or undercooked kidney beans, the protein can act as a toxin.

How to properly cook kidney beans and destroy toxins 

  • Beans should be soaked in water for at least five hours.
  • Soaking water should be dumped, and the beans should be boiled in fresh water for at least 30 minutes.
  • Do not use a slow cooker. Slow cookers do not get hot enough to destroy the toxins in kidney beans.

The science
Lectins are widely occurring, sugar-binding proteins, but some of them may become toxic at high levels. Lectins are known for their ability to agglutinate many mammalian red blood cell types, alter cell-membrane transport systems, alter cell permeability to proteins, and generally interfere with cellular metabolism, according to the Food and Drug Administration.

Among the lectins known to have toxic effects is phytohemagglutinin (PHA), which occurs at high levels in the seeds of legumes. This compound is the legumes seeds’ natural defense against plant pests and pathogens. PHA is destroyed by adequate cooking.

Some variation in toxin stability has been found at different temperatures. However, it has been found that boiling the beans for 10 minutes at 100 degrees C (212 degrees F) completely destroyed the toxin. To be safe, consumers should boil the beans for at least 30 minutes to ensure that the product reaches sufficient temperature, for a sufficient amount of time, to completely destroy the toxin.

Slow cookers should not be used to cook the beans or dishes that contain them. Studies of casseroles cooked in slow cookers revealed that the food only reached internal temperatures of 75 degrees C (167 degrees F) or less.

Several outbreaks have been associated with beans cooked in slow cookers or in casseroles that had not reached an internal temperature high enough to destroy the Lectin.

Symptoms of poisoning include vomiting and diarrhea within a few hours of eating the raw or undercooked beans. Only a few beans are needed to cause poisoning.

Diagnosis of this syndrome is difficult because it is not well known in the medical community and other possible causes, such as Bacillus cereus, staphylococcal food poisoning and chemical toxicity, must first be eliminated. However, if beans were a component of the poisoned victim’s meal, testing can be done based on the hemagglutination of red blood cells.

More in-depth information on beans and other foods can be found in the Food and Drug Administration’s Bad Bug Book.

You can also find general information on foodborne illnesses at

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