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I'm making 15 bean soup from a bagged dry bean mix that contains red kidney beans. Following the instructions, I soaked them overnight and threw out the water, but then thought I'd be clever and throw them in the slow cooker instead of cooking on the stove. They simmered in the cooker on high for probably about 15 hours (not entirely on purpose... I sort of forgot about them for a little while...)

Today I learned too late that kidney beans have a high amount of a toxin called phytohaemagglutinin, and you're supposed to boil them at least 10 minutes before putting them in the slow cooker. Apparently some slow cookers don't get hot enough to destroy the toxin no matter how long you cook them.

Can I just boil the soup on the stove after the fact to make it safe, or is it too late now? Is there any chance this will not turn my bean soup into unappetizing mush?

(It might be worth noting that Hurst beans, who makes the soup mix, has a slow cooker recipe on their website that says nothing about boiling them first.)

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I found this question interesting because I'd never heard of poisoning from red kidney beans before, and have certainly cooked them solely in the slow cooker without ill effects that I can recall, so I did a little internet research. Here's the most authoritative opinion I found:

Particularly, I found this specific advisory in at least 4 internet sources, including this one:

Beans cooked at 80 degrees Celsius, which is common in some of these cooking methods, increase the toxicity potential 5 times higher than eating raw beans.

This startling theory is never sourced anywhere; all of the sites I can find that mention it provide the information without attribution, even the serious medical ones. Many use the exact same words.

So it's up to you whether or not you believe this; personally, with a possible night of stomach cramps on the line, I would probably choose to dump them in a pot for a quick boil. On the other hand, I might consider what % of the soup is kidney beans and chance it.

  • Given that 5 beans is enough to cause real problems, if they're undercooked you're going to suffer, no matter what the proportions – Chris H Jul 7 '18 at 6:25
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    Possible source? ncbi.nlm.nih.gov/pmc/articles/PMC2271815/pdf/… – Yumecosmos Jul 10 '18 at 6:13
  • @Yumecosmos: yes, I think you have it, although that study specifically invalidates that theory. Typical. I've learned that when multiple articles fail to cite a source for a "health fact", it's probably false. – FuzzyChef Jul 11 '18 at 5:06
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Most slow cookers on high are probably hot enough. Probably isn't good enough.

I normally boil my beans for 10 minutes before putting them in the slow cooker (some sources say 30 but they cite sources that say 10). There's no safety reason (in anything I've read) why this boiling can't be done at the end instead, even though the texture might not be quite what you were aiming for.

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