Healthy Soy: Fermentation Makes Soybeans Digestible

Soybeans have a 35 to 40 percent protein content and are a perfect complement to the carbohydrates, proteins and amino acids found in the inner grain of rice. They have been a mainstay of the Japanese diet for centuries, but usually in a processed form, because they are almost indigestible otherwise. Many of these processing methods involve fermentation, and though the resulting product is sometimes salty, it is always more nutritious than the unfermented beans.


Miso is a fermented product made from soybeans and higher grades of polished rice, wheat or barley. Salt is added to preserve the mixture and malt to provide the fermentation enzymes. The quality of the miso is defined by the length of the fermentation process. Light sweet miso that is fermented for a short time is high in simple sugars, whereas the dark variety is higher in protein and contains more fatty acids. Very dark, older miso also contains a type of amino acids, known as umami, which is highly prized in Japanese cooking.

Shoyu and Tamari

Tamari is the liquid that pools on the surface of fermented miso whereas shoyu is a product that is brewed in its own right and not derived as by-product. Westerners tend to confuse these two products, but there is a big difference between them, especially for those who are gluten-intolerant. Shoyu is often brewed with wheat to temper the flavor, and is much more glutinous than tamari.

Properly brewed tamari and shoyu are far from the thin, salty liquids found in Chinese restaurants. They are rich and complex, much like fine wine, and the best varieties command a hefty price. The flavor varies with the vintage, the length of the fermentation process and the handling of the soybeans.


Cooked soybeans inoculated with natto bacillus and left to sit in a container at 40 degrees Centigrade for one or two days become natto ¬– a stringy, somewhat daunting concoction. It is full of enzymes, Vitamin B2, Vitamin K and protein and is much more digestible than unfermented soybeans because of the beneficial action of the natto bacillus. It is also an anti-oxidant and contains nattokinase, a blood thinner. Because the beans are allowed to ferment and grow bacteria, it is also a probiotic food. Natto has a strong smell and taste, and is definitely a acquired taste, but those who love it often enjoy it mixed with a little shoyu and mustard as an accompaniment to rice

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