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The Best Way to Cook Beans

Beans (also known as legumes) are an excellent source of protein and fibre, and are also one of the lowest GI (glycemic index) foods available. They are also relatively cheap.

However, legumes contain sugars known as galactooligosaccharides (GOS) which are non-digestible, and hence ferment in the gut. While they have benefits, such as being a prebiotic (stimulating the growth of healthy bacteria in the gut), the fermentation process can cause gassiness, bloating, flatulence and even nausea.

Furthermore, beans also contain compounds known as antinutrients, which prevent uptake of minerals and even protein. These include tannins, phytic acid and lectins. Some substances, such as the lectin phytohaemagglutinin, are even toxic.

Of note, there are also the following methods which while not described in the literature, I believe to have an effect:

  • Discarding cooking water after cooking (i.e. you must have used sufficient water to cook, more than the beans would absorb)
  • Rinsing the beans again after cooking
  • Combining the above

Reducing GOS

Percentages represent decrease compared to control.3

Method Raw Cooked Autoclaved
Unsoaked Control 40-45% 65-71%
Soaking 12H, water 40-45% 60-66% 74-77%
Soaking 12H, baking soda 43-48% 61-67% 77-80%
Sprouting 24H 41-51% - 62-83%
Sprouting 48H 80-88% - 83-93%
Sprouting 72H or more 100% - 100%

Notes:

  • Unless otherwise specified, cooking and autoclaving were done in water, and soaking water was discarded.
  • Autoclaving (121C, 15psi/103kPa) can be replicated at home with the use of a pressure cooker.
  • Cooking unsoaked beans in baking soda is generally more effective than in plain water, but the result varies depending on type of bean2, with some beans actually worse off with baking soda.
  • Soaking for 12H is more efective than 6H1. 12H appears to be the point beyond which additional soaking will not improve GOS/antinutrient loss significantly6. Soaking also appears to increase the soluble fibre content slightly, with no change in insoluble fibre content6.
  • Soaking in alkaline medium (e.g. baking soda), as compared to water, may cause a destruction of certain B vitamins3.

Reducing Antinutrients

Antinutrients can be classified broadly into two types, heat-stable and heat-sensitive. Heat-stable antinutrients are not easily destroyed with heat, but decrease with sprouting. Heat-sensitive antinutrients are destroyed with heat.

Examples of heat-stable antinutrients include tannins (decreases iron absorption) and phytic acid (decrease absorption of iron, zinc, magnesium and calcium).

Examples of heat-sensitive antinutrients include lectins (which interfere with absorption of calcium, iron, phosphorus and zinc), and saponins (which interfere with normal nutrient absorption).

Heat-stable antinutrients were best removed by sprouting for 24hr or more (87-100%). The combination of soaking and cooking/autoclaving was less effective (60+%) 35.

Heat-sensitive antinutrients were not significantly reduced by sprouting, but were removed almost totally by soaking and cooking/autoclaving.

In both cases, autoclaving was more effective than cooking.

Cooking with/without discarding soaking water

Tables from this paper4.

ANTINUTRIENTS RESULT OF DISCARDING SOAKING WATER
Phytates and phytic acid Desirable and greater loss
Total phenolic compounds Desirable and greater loss, most lost by cooking
Tannins Desirable and greater loss, most lost by cooking
Oligosaccharides Desirable and greater loss
NUTRIENTS RESULT OF DISCARDING SOAKING WATER
Proteins and respective digestibility Varied among studies. No influence.
Ashes, loss of solids, minerals and bioavailability Greater loss, but mineral bioavailability increases
Carbohydrates Varied among studies, does not decrease resistant starch content
Fibres Varied among studies. Reduces substances causing flatulence.

Notes on Sprouting

  • Mung beans are most often used.
  • Adding a weight on top of the sprouts, while they are growing, helps to make them plumper.

Conclusion

Applying heat is the best way to remove heat-sensitive antinutrients, while sprouting was the best way to remove GOS and heat-stable antinutrients.

Therefore, the best method, taking into account time considerations, would be to soak the beans for 24-48 hours (with not much more benefit over 48 hours), and subsequently autoclaving.

The second best method would be to soak the beans in water and then autoclave them, although this would result in slightly higher levels of GOS and antinutrients.

  1. Jood, S., Mehta, U., Singh, R., & Bhat, C. M. (1985). Effect of processing on flatus-producing factors in legumes. Journal of Agricultural and Food Chemistry, 33(2), 268-271. ↩

  2. Oboh, H. A., Muzquiz, M., Burbano, C., Cuadrado, C., Pedrosa, M. M., Ayet, G., & Osagie, A. U. (2000). Effect of soaking, cooking and germination on the oligosaccharide content of selected Nigerian legume seeds. Plant Foods for Human Nutrition, 55, 97-110. ↩

  3. Shimelis, E. A., & Rakshit, S. K. (2007). Effect of processing on antinutrients and in vitro protein digestibility of kidney bean (Phaseolus vulgaris L.) varieties grown in East Africa. Food chemistry, 103(1), 161-172. ↩↩↩

  4. Fernandes, A. C., Nishida, W., & da Costa Proença, R. P. (2010). Influence of soaking on the nutritional quality of common beans (Phaseolus vulgaris L.) cooked with or without the soaking water: a review. International journal of food science & technology, 45(11), 2209-2218. ↩

  5. Kalpanadevi, V., & Mohan, V. R. (2013). Effect of processing on antinutrients and in vitro protein digestibility of the underutilized legume, Vigna unguiculata (L.) Walp subsp. unguiculata. LWT-Food Science and Technology, 51(2), 455-461. ↩

  6. Njoumi, S., Josephe Amiot, M., Rochette, I., Bellagha, S., & Mouquet-Rivier, C. (2019). Soaking and cooking modify the alpha-galacto-oligosaccharide and dietary fibre content in five Mediterranean legumes. International Journal of Food Sciences and Nutrition, 70(5), 551-561. ↩↩

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