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I would like to try to cook some dried, red kidney beans via sous vide but am having difficulty finding anything authoritative on how to do this safely.

If you google "cooking beans safely" most articles point to this PDF from the FDA where on page 255 they say beans must be boiled for a minimum of 10 minutes but that 30 minutes is the recommended amount of time, otherwise the beans are not safe to eat.

I cannot find any chart that measures the amount of Phytohaemagglutinin against time and temperature. With such a chart it would be convenient to determine how long and at what temperature one must sous vide beans.

Most sous vide recipes online for beans I have seen recommend 6 hours at 190F, but I have not seen any data backing this as safe.

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  • You should include a question mark somewhere in your question
    – The Photon
    Jul 20, 2019 at 3:08
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    Related cooking.stackexchange.com/q/90849/35357
    – Debbie M.
    Jul 20, 2019 at 5:16
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    I've been trying to construct an answer for this question, but haven't come up with anything more definitive than the related question, and what @Chris H wrote. Being a user of sous vide myself, I guess I wonder why you would want to use that tool for the job. In terms of speed and safety, I think of pressure cooking first (my preferred method)...then, the boil method. Even without the potential risk, I would probably not choose sous vide for this task.
    – moscafj
    Jul 20, 2019 at 11:16
  • Agreed with moscafj. The benefits of sous vide (controlled temperature ceiling, no additional water content, sealed from evaporation) are unnecessary or undesirable for cooking dried beans.
    – Sneftel
    Jul 22, 2019 at 10:41
  • @moscafj The sole reason I was interested in sous vide over using a stove was to reduce the cost of cooking beans. Jul 22, 2019 at 16:34

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Given the temperature, it sounds like advice from slow cooking should apply - it's not far short of boiling. You can actually increase the (bioavailability of) phytohaemaglutinin by cooking at that sort of temperature for long periods unless you boil properly first. Only a few varieties of beans are an issue, mainly red kidney beans.

When slow cooking mixed bean chilli (for example), I soak the kidney beans separately from the other beans, then rinse them and bring them to the boil in plenty of new water for more than 10 minutes, discarding that water as well. You should do something similar. It's not all that convenient, but it is necessary.

The chart you'd like would be difficult to produce because each bean isn't at a uniform temperature - 10 minutes becomes 30 to ensure the low of each bean gets hot enough. The amount in a particular batch of beans will be quite variable as well.

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I agree it might be much easier to just use a pot.

That said, I did find on Wiki that 2 hours at 80 C / 176 F will make them safe. I didn't track down the source (it looks legit in the reference) so you'll need to verify yourself.

https://en.wikipedia.org/wiki/Phytohaemagglutinin

Measured in haemagglutinating units (hau), a raw red kidney bean may contain up to 70,000 hau. This can be reduced to safe levels by correct cooking by boiling unsoaked beans for at least 30 minutes, presoaked beans for 15 minutes, 2 hours at 80 °C (176 °F), or 45 minutes pressure cooked at 15 psi.[5][6] Insufficient cooking, such as in a slow cooker at 75 °C/ 167 °F, may not completely destroy the toxins.

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  • It's worth reading the Thomson paper (academia.edu, free but annoying) has it for download. From the abstract: At 65”C, no significant decrease was observed even after 12 hr heat treatment and from the introduction A recent study of Bender (1981) in fact showed an increase in activity after heat treatment at 80°C for 45 min. But the paper is correctly cited in that it says At 80°C, lectin activity decreased to below detectable levels in 2 hr.
    – Chris H
    Jan 28, 2022 at 9:04
  • So if you can be sure you get to 80°C for more than 2 hours, through the whole volume that paper suggests you should be safe. Sous vide should ensure the temperature better than my slow cooker, which I don't measure though I'm pretty sure it gets well above 80°C on high, but heat penetration to the middle is still an issue to be wary of.
    – Chris H
    Jan 28, 2022 at 9:06

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