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I'd like to cook beans from dried, but I see a lot of contradictory safety advice about neutralising the toxins that occur in raw beans.

I've seen:

  • Rolling boil for 5 mins before simmering until tender.
  • Rolling boil for 10 mins before simmering until tender (that's what's on the cooking instructions on the back of my pack of cannellini beans, for example)
  • Rolling boil for 30 mins... (that was the FDA)
  • Just bring to a boil then simmer (lots of American recipe sources recommend this)

I assume there's maybe a trade off between safety/pleasantness i.e. hard boiling for longer at the start might result in less nice beans, but a lesser chance of poisoning?

Can anyone clarify the science on this? Why does advice vary so widely?

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  • which toxins are you referring to? Ricin is produced from castor beans, but those types of beans are not usually used to cook with.
    – Neil Meyer
    Feb 13 at 11:47
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    @NeilMeyer phytohaemaglutin in red kidney beans is the normal concern. That's destroyed by boiling. Different advice may apply to different beans, explaining the discrepancy. Pretty sure we've got at least one question covering this already, but no time to search now
    – Chris H
    Feb 13 at 12:34
  • Lectins web.archive.org/web/20170310134645/https://www.fda.gov/Food/…
    – samfrances
    Feb 13 at 12:35
  • @ChrisH The 30 minute advice was for kidney beans, but I have had read the 5 minute, 10 minute and "just bring to boil then simmer" advice for cannellini beans / generic "white beans", so there's still discrepancies for the same bean. Also not sure of the extent to which the 30 minute advice applied to cannellini beans, since the advice was for "kidney beans", of which cannellini beans are apparently a subclass.
    – samfrances
    Feb 13 at 12:37
  • "kidney beans" normally refers to red kidney beans even though cannellini beans are sometimes called "white kidney beans". Lots of beans are the same species but the toxin levels in red kidney beans are much higher than other varieties. Brief boils, less than 10 minutes come from the recipe writer's preference. Some sources say soak, rinse, bring to boil from cold, 10 minutes boil, rinse again is enough for (red) kidney beans even before slow cooking, but others say 30 minutes.
    – Chris H
    Feb 13 at 14:48

2 Answers 2

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Per discussion, we are talking about Phytohemagglutinins as "toxins".

Current research indicates that, regardless of the rest of your cooking routine, you should cook kidney beans at 100C (a roiling boil) for at least 5 minutes. Lower temperatures (90C to 97C) may also destroy the lectins, but they might not. This has obvious issues for folks living at altitude.

Many sources will recommend more than 5 minutes in order to make sure that cooks have the beans at 100C for at least 5 minutes.

Kidney beans are quite hearty; boiling them for 10 minutes will not harm their texture in any way.

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Time will also vary depending on pretreatment. I have seen recipes that cook beans over an hour if you skip presoaking the beans overnight.

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    I am not sure this answers the question? This post seems to be about cooking time until tender, but the question is specifically about food safety and about the parameters necessary to destroy lectins?
    – Stephie ♦
    Feb 13 at 16:58

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