Close-up of kidney beans
The culprit of this intestinal mayhem is the toxin Phytohaemagglutinin (Kidney Bean Lectin) found in quite a few beans, though kidney beans have the highest amount. For example, raw kidney beans contain between 20,000 and 70,000 hau (hemagglutinating units) while white ones contain a third of that and broad beans only contain 5-10% of the figure. The operative word here is ‘raw.’ Once they are cooked properly, they are detoxified.
Single seedling germinating early
Phytohemagglutinin, the sinister chemical that goes along with all the healthy ones that make kidney beans great, makes you very ill, starting with nausea and then onto extreme vomiting and finally ending in waves of diarrhea. You need to ingest a large amount of the compound but the bad news is that only three beans can be considered a high enough amount!
Boiled kidney beans
The reason you may not have heard of the kidney beans’ toxicity is twofold. One: most of the time kidney beans are properly soaked and cooked (it only takes 10 minutes at a high temperature to detoxify them) and of course canned ones are safe as can be due to having been processed.
Kidney bean flower
As very few people, if any eat, raw beans, you might wonder why it is an issue at all. Well this little nasty bacteria has a secret curve ball to throw. If they are undercooked rather than raw or completely cooked at a high temperature (they absolutely must boil for 10 minutes) kidney beans at an internal temperature of 75 or 80 degrees increase their toxicity level 5 times over raw beans!
Kidney beans being cooked
Many to most slow cookers or stews cooked at a gentle simmer will not reach temperatures high enough to render the beans safe. Tests have found slow cookers are often only at 75 degrees. This is fine for a long 8 hour simmer of almost all ingredients apart from kidney beans. Some people blame the symptoms on a bad stomach, bad salad or mayo in a meal when it is really the beans. The good news? It generally resolves within 4 or 5 hours, though some victims need hospitalization.