Soaking dried legumes: digestion, minerals and preparation

Dry seeds absorb water and swell. This hydration shortens cooking time and gives a more tender, even texture. It never replaces thorough cooking.

Soaking also changes the liquid. Some of the sugars in the raffinose family, the alpha-galacto-oligosaccharides, leach into the water. These sugars are fermented by gut bacteria and can cause gas in some people. A 2019 study on five Mediterranean legumes measured their decrease during soaking: about 10% for lentils and fava beans, about 40% for chickpeas, with a further decrease during cooking. These figures apply to the conditions studied, not to every pot.

Phytates are compounds naturally present in seeds. They can bind to iron and zinc and reduce their absorption. A review on the common bean notes that reducing phytic acid improves iron availability, which explains the interest in soaking, sprouting, or fermentation.

Household soaking, however, only reduces part of the phytates, in variable proportions. It doesn't turn a legume into a mineral supplement. And discarding the water also carries away a fraction of minerals: there's no single nutritional rule.

If beans cause you bloating, start by soaking and then discarding the water. If you digest them well, keeping the water isn't a mistake. Either way, cooking until tender remains the deciding factor.

Dried kidney beans contain a lectin, phytohaemagglutinin, destroyed by thorough boiling, but not by soaking alone or by insufficient cooking. In 2018, in Brittany, France, undercooked kidney beans in a chili con carne made about 200 of 1,700 diners sick, with digestive symptoms appearing within a few hours.

1. 01Sort the seeds, remove debris or damaged ones, then rinse them.
2. 02Cover generously with water. For a long soak, place the container in the refrigerator.
3. 03Drain and rinse if you choose to discard the water.
4. 04Cook in fresh water until the seeds are tender all the way through.
5. 05Cool leftovers quickly and store them in the refrigerator.

The quick method is to bring the seeds and water to a boil, turn off the heat, cover, let sit for about an hour, then drain before cooking. Lentils, split peas, and black-eyed peas generally don't need soaking, but they too must be cooked thoroughly.

It doesn't "detoxify" a legume and doesn't fully eliminate phytates, lectins, or fermentable sugars. Undercooking, a large portion, or a sudden increase in fiber often cause more discomfort than the choice of soaking water. Canned legumes, already cooked, are a convenient alternative: rinsing them reduces some of the liquid and salt. For combining them in meals, see the article plant proteins: do you need to combine foods at every meal?.

In case of persistent pain, diarrhea, vomiting, or an allergic reaction, ask for medical advice rather than multiplying culinary tricks.