I was reading up on toxic foods when I saw them on the list: kidney beans.

Toxic kidney beans? That was new information for me, and it didn’t make sense. Just weeks earlier, I’d eaten a tossed salad with cold kidney beans in the mix, and I had noticed no side effects. Could kidney beans really be toxic?

As it turns out, the toxin Phytohaemagglutinin occurs naturally in several kinds of raw beans, including broad beans, white kidney beans, and red kidney beans. This toxin causes gastroenteritis, an unpleasant condition that sends most folks to the bathroom.

Boiling beans

The good news is that the toxin can be deactivated by simply boiling the raw beans for ten minutes. This temperature degrades the toxin without cooking the beans. The FDA also recommends soaking the beans for five hours to remove any residual toxins and then tossing the water out. Canned beans go through a pressurized canning process that makes them safe to eat, which explains why my salad didn’t give me gastrointestinal trouble.

The dangers of raw beans

The danger comes from eating raw beans or undercooked beans. Eating just four raw, soaked beans is enough to cause symptoms of foodborne illness. Crockpots are popular methods for cooking raw beans, but this method can yield dangerous results. Slow cooking raw beans normally requires hours of cooking on a low setting, but crockpot temperatures vary. If the low setting on a crockpot is below 180°F, then slow cooking the beans won’t make them safe to eat. In fact, undercooking beans increases the toxicity by five times. Yikes!

The moral of the story is to eat beans from a can or to boil raw beans properly before cooking. For added safety, follow the FDA recommendation to soak beans for five hours before cooking them. Kidney beans may be toxic, but they’re easy to cure for good eating.

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—Suzanna Sandridge

Editor’s note: This post was originally published in July 2014 and has been updated for freshness, accuracy, and comprehensiveness.