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Saturday, October 13, 2012

A method for cooking dried beans to increase mineral absorption

As the one in our family who does the grocery shopping and meal prep, I've always taken an interest in nutrition. I read up on foods that are new to me. I loosely track the nutrient content of our meals (I say loosely, because I'm not counting grams or anything that specific. I just pay attention to the key nutrients in the foods that I've planned for us to eat, and try to keep everything in balance.) And I seek out foods to fill what I believe could become nutrient deficits in our diet.

Recently I was researching magnesium, iron and zinc. The information that I learned about these, and other minerals, and their absorption came as something of a surprise. And I have now changed the way I prepare some foods, specifically dried legumes.

We know that dried legumes are an inexpensive source of protein, as well as other nutrients. In our family we have some form of beans several nights of the week. However, many of us are not absorbing the maximum nutrients from beans, due to our soaking process. We are losing out on a good share of calcium, magnesium, iron and zinc.

A better method for soaking your dried beans

For many years, I thought that a quick soak (bring beans and water to a boil, turn off the heat and let sit for 1 hour), was as good as a long overnight soak. In fact, while the long overnight soak is better than a quick soak, there's an even better method for soaking dried legumes.

As it turns out, there's a component in these dried beans called phytic acid. (Phytic acid is also present in whole grains, nuts and seeds.)  Phytic acid binds key minerals, preventing our digestive system from adequately absorbing them. And it inhibits the production of digestive enzymes, resulting in gastrointestinal problems.

There's no need to give up beans, however. Several studies have found that soaking dried beans in very warm water for about 24 hours, reduces the phytic acid levels substantially. The optimum temperature for a soak is 140 degrees F. But for practical purposes, there's a simplified method for this soak, resulting in significantly reduce levels of phytic acid.

  • Begin the morning of the day before you plan to cook the beans. 
  • Rinse your beans. 
  • Bring a kettle of water to a boil. 
  • Place beans in a large vessel and pour equal parts boiling water and tap water over the beans, yes, equal parts boiling and room temp water. This will give you roughly 140 degrees F. 
  • Put the lid on, and place in the warmest part of your kitchen, without actually heating your pot. If you'll be cooking on the stove or in the oven, place it very close. 
  • As the water is absorbed throughout the day, add more. 
  • Allow to soak for about 24 hours.
  • The next morning, pour off all the soaking water, and rinse well. 

  • For cooked, plain beans (to add to bean and rice mixtures, to marinate, or for making refried beans), add new water and begin your cooking process. When all cooked, pour off this water and rinse well again.
  • For making a soup, where you want to flavor your beans, after rinsing the soaked beans, begin the cooking process with vegetables, soup bone, seasonings, etc. 
The long soak in warm water will result in beans with significantly-reduced phytic acid levels. Your beans will not only provide you with higher mineral absorption, but will be more digestible as well.

Have a look at these 3 articles for more detailed info on mineral absorption and phytic acid, herehere and here. The first two articles discuss beans in specific, and the preferred method of soaking. The third of these articles gives in depth information on phytates, and grains, nuts and seeds, and how to counteract some of the complications stemming from high phytate content in these foods.

edited 10/13 8:45 AM  reason: to include additional cooking information


  1. Interesting information. How do you handle using the beans in a soup - say, when you begin cooking them with a ham bone and vegetables and herbs? I believe part of the purpose of adding these items is to flavor the beans as well as the broth. I will keep this in mind for the fall, when beans and soup play a more dominant role in our diets.

    1. Hi Valarie,
      Ooops! I left out cooking with seasonings and bones. The above directions are if you want cooked plain beans, for something like rice and beans, or refried beans, or marinated beans.

      I'll adjust the text above. For making a soup, after the long 24 hour soak, drain and rinse your beans, then cook as usual adding veggies and soup bones, etc.

      I have been thinking how best to cook lentils and split peas, as those are usually added dry to the soup liquid. I think I'll be soaking those, too.

      Sorry about leaving something off. And thanks for asking!

  2. Thank you for the information. I use only dried beans, and always used the over night soak, but never realized I should have them in hot water. I then cook mine in the slow cooker.

    For lentils and split peas, couldn't you do a shorter hot water soak, then you wouldn't have as long to cook them. My favorite soup is split pea so I thought I would try this method after reading your post.

    1. Hi Lois,
      From what I've been reading, it looks like best mineral absorption is obtained from a long warm water soak, drain, rinse, then cook. I've read as little as 18 hours, as long as 36 hours for the soak on all legumes. Most of the data indicates that a 24 hour warm water soak on all types of legumes (including lentils, split peas and blackeyed peas) will reduce the phytic acid to levels that allow good mineral absorption.

      Anyways, I'll be using this method even for split peas and lentils. Although our family is not vegetarian, we do eat a lot of legumes, several days per week, and this info took me by surprise.

      An interesting thing about these studies and articles is I found them under a variety of health-related topics, from articles on depression, dental decay and osteoporosis (so I see the link between dental and bone issues, but also depression).

      As I learn more, I'll post additionally on this topic. Thanks for your interest.

  3. That's really interesting. I usually go for a long soak if I'm organised enough but always with boiling water to start with. Once I get my food thermometer I shall be able to make sure the temperature is just right! :-)

    1. Hi Sarah,
      That's good that you do a long soak (and starting with hot water, too). You're probably minimizing the phytates that bind minerals.

  4. Thank you so much for this information! I'll definitely put it to use going into the cooler months when we eat more soups.

    1. Hi Sharon,
      Your welcome. Glad to be of help.

  5. This is interesting. I do feel like I don't get enough iron. We use dried beans quite a lot in the colder months, mostly in soups, but also in a favorite casserole from my mother's recipe file. I'll use this method. Thanks for sharing.

    1. You're welcome, Helen. While I'm sure this is not the definitive answer to feeling low in iron, it is something we can do to increase our bodies' iron absorption. I'd love to hear what's in your mother's casserole recipe.


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