How to Cook Black Beans to Remove Toxins

All legumes, including black beans, contain a compound called phytohemagglutinin, which can be toxic in large amounts. This is a serious problem with red beans as well, which contain such high amounts of this substance that raw or undercooked beans can be toxic when consumed.

However, the amount of phytohemagglutinin in black beans is generally significantly lower than in red beans, and toxicity reports have not been associated with this component.

If you still have doubts about phytohemagglutinin, then the good news for you is that careful cooking reduces the amount of toxins in beans.

Black beans need long soaking (12 hours) and rinsing. This in itself removes toxins. After soaking and rinsing, bring the beans to a boil and skim off the foam. Experts recommend boiling the beans over high heat for at least 10 minutes before drinking. You should not cook dried beans over low heat, because by doing this we do not destroy, but only increase the content of the phytohemagglutinin toxin.

Toxic compounds such as phytohemagglutinin, lectin, are present in many common varieties of legumes, but red beans are especially abundant. White beans contain three times less toxins than red varieties.

Phytohemagglutinin can be deactivated by boiling the beans for ten minutes. Ten minutes at 100° is enough to neutralize the toxin, but not enough to cook the beans. Dry beans must first be kept in water for at least 5 hours, which should then be drained.

If beans are cooked below boiling (and without pre-boiling), on low heat, the toxic effect of hemagglutinin is increased: beans cooked at 80 °C have been known to be up to five times more toxic than raw beans. Cases of poisoning have been associated with cooking beans over low heat.

The primary symptoms of phytohemagglutinin poisoning are nausea, vomiting, and diarrhea. They begin to appear one to three hours after consumption of improperly cooked beans, and symptoms usually resolve within a few hours. Consuming as few as four or five raw or unsoaked and unboiled beans can cause symptoms.

Beans are known for their high content of purines, which are metabolized into uric acid. Uric acid is not a toxin per se, but may contribute to the development or aggravation of gout. For this reason, people with gout are often advised to limit their intake of beans.

It’s very good to cook all beans in a pressure cooker that maintains a temperature well above the boiling point during the cook time and during pressure relief. It also greatly reduces the cooking time.  


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