I think there might have to be a Part 3 (and, who knows, maybe a Part 4, 5, and 6) to deal with all the questions regarding soaking foods. I might not do them in consecutive posts.

The flatulence caused by eating beans is normally attributed to the oligosaccharide content of the beans. Oligosaccharides are chains of sugar molecules, usually two to ten in length, and comprising of at least some sugars other than glucose. (Long chains of glucose-only molecules are considered starches and are typically easy to digest.)

The flatulence is caused by the fact that humans do not have digestive enzymes to break down the oligosaccharides and, instead, they are broken down by bacteria in the lower intestines which produce gas in the process.

Soaking reduces the amount of oligosaccharides in beans. But how does it compare to simply cooking? Unfortunately, in the time I had to search, I did not find a study that compared soaking and cooking to only cooking. But I did find a study that compared the oligosaccharide reduction in pinto beans among different preparation methods (1):

– Soaking for 18 hours: 10% reduction
– Soaking for 18 hours, then boiling for 90 minutes: 50% reduction
– Soaking for 18 hours, then autoclaving for 30 minutes: 57% reduction

Autoclaving is approximately the same as pressure-cooking.

It’s not clear from this study that you first need to soak the pinto beans to produce the 50% reduction in oligosaccharides.

In her article on reducing flatulence in veg diets, Dina Aronson, MS, RD suggests, “If you make beans from scratch, soak them overnight first, rinse them well, and rinse them several times during the cooking process, as this will help get rid of more of the gas-causing oligosaccharides. Also, the longer you cook beans (with rinsing), the better.”

It should also be noted that in their comments, the authors of the study above say, “Soaking of Great Northern, kidney, and pinto beans and their subsequent boiling for 90 min decreased the amount of [the oligosaccharides] raffinose and stachyose by 70-80%. In marked contrast, sucrose, raffinose, stachyose, and verbascose contents increased [emphasis added] following the cooking of red, Bengal, black, and green grams (1).”

Sigh. Luckily, I don’t think too many of us eat “grams,” so we probably don’t need to worry about that. I looked up the study and they did not soak the beans before cooking, so perhaps that was the problem (2).

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References

1. Song D, Chang SK. Enzymatic degradation of oligosaccharides in pinto bean flour. J Agric Food Chem. 2006 Feb 22;54(4):1296-301. | link

2. Rao PU, Belavady B. Oligosaccharides in pulses: varietal differences and effects of cooking and germination. J. Agric. Food Chem. 1978 26:316-319 | link

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