Fermented soybean products

Fermented soy products include sufu, miso, soy sauce, tempeh, and natto.  

Fermented bean curd or sufu (tou fu ru, fu ru) is the vegetarian equivalent to mold-ripened milk cheeses.

Most fermented soybean products suffer a two-stage fermentation process where to start, dormant green spores of Aspergillus molds are mixed with cooked grains or soybeans, and kept well aerated and moist. The spores germinate and produce digestive enzymes that break down the beans/grains. After two days, the enzymes are at their peak. The mixture, called chhü in China and koji in Japan, is immersed in salt brine and more cooked soybeans. In this oxygen-poor brine, the molds die, but their enzymes continue to work. To end, anaerobic, salt-tolerant lactic-acid bacteria and yeasts grow in the brine and contribute their own flavorful by-products to the mixture.

Traditionally miso making allows the mixture to ferment for months to years at a warm temperature. Browning reactions generate deeper layers of color and flavor. Modern, industrial production cuts the fermentation and aging from months to weeks, and compensates the resulting lack of color and flavor with additives.

Soy sauce in the West is mostly Japanese soy sauce, which includes an even mixture of soybeans and wheat. The starch from the wheat gives it a characteristic sweetness, higher alcohol content, lighter flavor and color. 

Chinese soy sauce and Japanese tamari are almost exclusively made from soybeans. It is darker in color and richer in flavor due to the higher concentration of soybean amino acids. 

“Chemical” soy sauce is a non-fermented approximation of soy sauce that uses defatted soy meal left over from soybean oil production and is hydrolyzed with concentrated hydrochloric acid. The mixture is neutralized with sodium carbonate and later flavored and colored with corn syrup, caramel, water, and salt. To make it more palatable, it is blended with some portion of genuine fermented soy sauce. To ensure buying genuine soy sauce, avoid labels containing added flavorings and color.

Tempeh originated from Indonesia and is a perishable main ingredient, not a preserved condiment. It is made by cooking the whole soybeans, placed in thin layers, and fermented with a mold. The mold forms hyphae that binds the beans together and digests proteins and fats that turns it into flavorful bits. Fresh tempeh develops a nutty, almost meaty flavor when sliced and fried.

Natto, like tempeh is a perishable product. It is notably alkaline and develops a sticky, slippery slime that can be drawn with the tip of a chopstick into threads up to 3 ft/1 m long. It is made from whole cooked beans and inoculated with a culture of Bacillus bacteria and held at warm temperatures for 20 hrs. Its stringiness derives from long chains of glutamic acid and long branched chains of sucrose.