No. NO! Seriously, it is not safe. Red kidney beans contain a potent toxin called phytohaemagglutinin which can cause severe gastrointestinal symptoms, including nausea, vomiting, and diarrhea. Fortunately, this toxin is deactivated by the heat of boiling. So boiled kidney beans, and this includes canned beans, are perfectly safe. But slow cooking uses lower temperatures than boiling, which is 212 degrees Fahrenheit. The actual temperature reached in a slow cooker varies by model and the setting used, but it is always below boiling−this is the very definition of slow cooking! Thus, the toxin in kidney beans will not be deactivated, at least not fully, by slow cooking.
You can safely cook kidney beans in a slow cooker if you soak them overnight and then boil them for 10 minutes before putting in the slow cooker, but it hardly seems worth the trouble! And as I already mentioned, canned kidney beans are perfectly safe.
By the way, other beans (for example cannelini and turtle beans) also contain phytohaemagglutinin but in much lower concentrations than red kidney beans. I have not seen any warnings about cooking those in a slow cooker.
They are, to tell the truth, quite similar. But not the same. In most cases it does not make any practical difference. Navy beans are smaller yet take longer to cook than great northern beans. They feature in famous recipes such as Boston baked beans and Senate bean soup. But great northern beans taste pretty much the same. So don’t worry about which kind you have as long as you are aware of the cooking time difference.
There are three “facts” you’ll often hear about cooking dried beans, such as kidney and great northern beans. It turns out they are all myths.
- You must soak beans before cooking. You can soak beans of course, but the only advantage it provides is to shorten the cooking time. There’s no reason not to start cooking dry beans directly as long as you have the time to simmer them long enough.
- You must not add salt to beans during cooking or they will not soften. Tests show that the only difference between beans cooked side by side with and without salt is that one is salty and the other is not. Some people feel that salting during cooking gives better flavor because some of the salt ends up inside the beans.
- You must not add acid, such as tomatoes, to beans during cooking or they will not soften. Acid does in fact have an effect on beans, tending to keep the skins intact, while alkaline substances (baking soda) help the skins to break down. In both cases however the beans cook perfectly well. You can use this to your advantage, adding tomatoes during or after cooking depending on whether you want whole beans or mushy beans.
Note, however, soaking can help reduce the “gas attack” effect that some people experience after eating beans. Bring dry beans and water to a boil, remove from heat, and let sit for an hour. Drain, add fresh water, and continue cooking. This removes some of the chemicals in the beans that cause the gas.
