Slow Cookers and Red Kidney Bean Poisoning

I have to publish my first major retraction today. I can’t believe I didn’t know about this before, but…do NOT follow my old slow cooker beans technique when cooking beans, especially kidney beans, cannelini beans, or broad beans.

Old Technique:
Put the beans and 8 cups of water into the slow cooker. Cook on low for 8 hours.

Do this instead:
Put the beans in a pot, cover with 2 inches of water, and bring to a boil. Boil for ten minutes, then drain. Put the drained beans into the slow cooker and add 8 cups of water. Cook on low for 8 hours.

Red kidney beans contain high levels of a toxin that occurs naturally in beans, Phytohaemagglutinin (also known as Kidney Bean Lectin.) If raw or undercooked red kidney beans are eaten…well, bad things happen. Let’s just say you’ll be getting to know the pattern of tiles in your bathroom very well.
For all the gory details, check here.

With normal cooking, this isn’t a problem. The toxin is destroyed after ten minutes of boiling (cooking at 212*F or 100*C.), and most stovetop recipes easily take care of the toxin with their hours of simmering at that temperature. Raw, soaked beans are bad; eating four of them is enough to cause symptoms. Now, here’s the problem with slow cookers: undercooked beans (cooked at 80*C, roughly 170*F) increase the toxicity fivefold. And, most slow cookers have their “low” setting at about 180*F. If your slow cooker runs a little cooler than most… England tracks this more carefully than we do here in the US. They had seven outbreaks of kidney bean poisoning between 1976 and 1979, caused by raw, soaked kidney beans or kidney beans cooked in a slow cooker.

The toxin occurs in red kidney beans, and to a lesser extent in white kidney beans (cannellini beans) and broad beans. Other beans contain the toxin, but at much lower levels.

How did I miss this? I never had, um, gastrointestinal issues from slow cooked kidney beans. My slow cookers must run hot enough that the toxin was destroyed. Also, I prefer black or pinto beans to kidney beans, so those are the beans I’m usually slow cooking. In the future, I am always going to boil my beans for at least 10 minutes before cooking them in a slow cooker. This takes some of the simplicity out of the “dump and cook” technique that I use, but it’s still pretty simple. And the alternative is not pretty.

I want to extend my sincere apologies to anyone who followed my technique. I hope I didn’t cause you any…problems.

References: Phytohaemagglutinin (Kidney Bean Lectin) []

Related posts: Basic Technique: Slow Cooker Dried Beans


  1. Well, who knew??? I’ve cooked beans in the slow cooker forever, I had NO idea. Thank you for making me aware!

  2. @Linda:

    I think your slow cooker (and mine) run hot enough – that’s why I never had any problems with my old recipe. But…I don’t want to have someone get an unfortunate surprise if they have a slow cooker with a lower “low” setting than mine. Better safe than sorry…

  3. Linda Watson /

    Nice to meet a fellow cooking geek! I ran across your post while looking for any current cases of kidney-bean poisoning in the U.S. (so far, nothing).

    I don’t think your original method for kidney beans was wrong as long as they boiled for 10 minutes at some time during the cooking process. With my old slow cooker even on low, the beans boil away merrily well before they are finished cooking. (For non-geeks, I’ll mention that as long as the water has even a slow boil, with just a few bubbles rising, it’s as hot as it’s going to get.)

    Glad you are helping to spread the word about changing the soaking water and not eating partly cooked beans. And whoo-hoo for cooking dinner every night!

    … Linda at

  4. Anonymous /

    My wife and I got very sick from red kidney beans in a slow cooker, I did some research, you are right many people never had this problem, and here is the reason. Old slow cookers run hotter than the new ones. At some point they lowered the top temperature of new slow cookers for safety reasons, so if you have an older slow cooker, you could get away without boiling the beans first but if you get a new one you won’t be so lucky. I contacted several bean suppliers and asked them to change their labelling, they said they would but here we are several years later and they haven’t changed a thing, I hope this helps, take care.

  5. Anonymous /

    (For non-geeks, I’ll mention that as long as the water has even a slow boil, with just a few bubbles rising, it’s as hot as it’s going to get.)

    This is incorrect. A rolling boil is approximately 7 degrees hotter than a slow boil, and about 12-27 degrees hotter than a simmer.

  6. Why would any one want to eat something that has to be soaked overnight, then boiled for hours before you can eat it to get toxins out?? Why eat anything that once held toxins??

  7. Because they taste so good…once you’ve cooked them enough.

  8. Tami /

    Actually, I understand it to be the opposite; the newer slow cookers cook hotter for health safety reasons than the older slow cookers, which is why I didn’t use to have to add water to some things that I now have to because of a newer, hotter cooker.

  9. Tami /

    Would it be sufficient to just cook it on high for part of the time? Would that get it hot enough? I had never heard of this toxin issue either before now.

  10. Eric S /

    Don’t forget that 10+ minutes of boiling will destroy the toxin. Slow cooking is still a good method to cook a great bean. My new-ish cooker hits a boil on high. After many hours on a lower setting, it only takes about 10 minutes on high to get to a boil and then 10 to make it safe, and that short time won’t kill your beans. If your cooker won’t boil, transferring to a pot on the stove will do it. We usually just go from the cooker on low straight to a pot anyway since we’re usually adding our beans to soup and the soups need a bit of boil to meld flavors.

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