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.

Palatable soybean forms (non-fermented)

• A few legumes are parched in dry heat to create a crisp texture. Peanuts are the most commonly roasted legumes, but soybeans and chickpeas are also roasted.
• Fresh soybeans are more palatable before they fully mature. Fresh soybeans, Japanese edamame, or Chinese mao dou are special varieties harvested at 80% maturity. They have lower levels of gassy and antinutritional substances.  The beans are sweet, crisp, and green. They are boiled for a few minutes in salted water. Green soybeans are around 15% protein and 10% oil.
• Soy milk has become a popular alternative to cow’s milk, though it must be fortified with calcium to make it an adequate substitute.
• The traditional method of making soy milk involves soaking the beans until soft, grinding them, and either sieving out the solids and cooking the milk (China) or cooking the slurry, then sieving out the solids (Japan). This process produces milk with a strong soy flavor.
• Modern method minimizes enzyme action and soy flavor. The dry beans are soaked, then either cooked quickly at 180-212 degrees F/80-100 degrees C before grinding, or grinding them at that temperature. 
• Bean curd or Tofu is curdled soy milk, a concentrated mass of protein and oil formed by coagulating the dissolved proteins with salts. Invented in China around 2,000 years ago, the Chinese have traditionally coagulated with calcium sulfate. The Japanese and coastal regions of China coagulate it with nigari, a mixture of magnesium and calcium salts that are left over after sodium chloride is crystallized from seawater.
• To make it, soy milk is cooled to 175 degrees F/78 degrees C, and then coagulated with salts. The curd is pressed to form a continuous mass. Commercially, it is cut in blocks and pasteurized.
• Freezing bean curd is a useful application as it concentrates the proteins. Once thawed, the liquid leaks out, and leaves a spongy network that is ready to absorb other flavors. It also develops a chewier, meatier texture.

Soybeans and health

In On Food and Cooking, Harold McGee describes the soybean as

“exceptionally nutritious, with double the protein content of other legumes, a near ideal balance of amino acids, a rich endowment of oil, and a number of minor constituents that may contribute to long-term health.” page 493.

Soybeans contain storage forms of isoflavones. These are phenolic compounds are liberated by intestinal bacteria as phytoestrogens, a form that resembles the hormone estrogen. Boiled whole beans contain the most isoflavones. Some research suggests that they may slow bone loss, prostate cancer, and heart disease, but due to their hormone-like effects on the body, soybeans can worsen pre-existing breast cancer. This process is not completely understood.

Soy beans are also a rich source of saponins, which are soap-like defensive compounds that are both, water- and fat-soluble. Soy saponins bind cholesterol so that the body can’t absorb it efficiently. Furthermore, soybeans have phytosterols, chemical relatives of cholesterol, which also interfere with cholesterol absorbtion.

For all their goodness, soybeans are at the same time, unappealing. They contain abundant antinutritional factors, fiber, and oligosaccharides. They contain negligible amounts of starch. Their texture tends to remain firm. To make them more appealing, the Chinese and others have developed ways to alter their taste, such as via extraction of the protein and fermentation.

Common legumes (not including peanuts)

Fava or Broad Beans – Vicia faba – are the largest legume. They originated in Asia and are believed the earliest domesticated plant. Evidence of cultivation found in Mediterranean sites date back to 3000 BCE. Today, China is the world’s largest producer.

People who have an inherited G6PD deficiency should not consume fava beans as they can develop a hemolytic reaction called “favism.”  Fava beans contain two unusual amino-acid relatives, vicine and convicine, which are oxidants that become toxic to people with an inadequate supply of glutathione, as are people with G6PD deficiency. Favism is found most commonly in the southern Mediterranean and Middle East. In areas where malaria has been historically endemic, G6PD deficiency appears to have been a result of natural selection, as it suppresses the growth of the malaria parasite in red blood cells.

Chickpea/Garbanzo is native of southwest Asia. Two main varieties are available: desi and kabuli. Desi are small, thick, tough seed coat, and dark. These are mainly grown in Asia, Iran, Ethiopia, and Mexico. The kabuli type is most common in the Middle East and Mediterranean. It is larger, cream-colored, with a light seed coat. Chickpeas have 5% oil by weight compared to 1-2% of other legumes.

Hummus is a chickpea paste usually flavored with garlic, paprika, and lemon. Chickpeas are the most important legume in India.

Common bean is native of southwestern Mexico, and most widely consumed in Latin America. The common bean has developed hundreds of varieties. Large varieties originally from the Andes, include kidney, cranberry, large red, and white. Smaller-seeded Central American types include pinto, black, small red, and white.

Popping bean or nuña is cultivated in the high Andes. It can be popped in 3-4 min of high dry heat (i.e. microwave). It does not expand as much as popcorn as it remains fairly dense, with powdery texture and nutty flavor.

Lima bean originated from Peru (named for its capital of Lima). It was introduced to Africa via the slave trade, where today they remain the main legume in the African tropics. Some wild types contain potentially toxic quantities of cyanide, so they must be cooked thoroughly to be safe. Commercial varieties are cyanide-free.

Tepary beans are native of the American southwest, and are unusually tolerant of heat and water stress. They are rich in protein, iron, calcium, and fiber. Tepary have a distinctive sweet flavor.

Lentil is probably the oldest cultivated legume. Native of Southwest Asia, there are two groups: large flat (>5mm across) and small rounded (<5mm). Large are most commonly grown. Varieties include brown, red, or green seed coats. Their flat shape and thin seed coats allows water to penetrate easily, thus they cook quickly, in  one hour or less.

Peas are a cool climate legume. Historically, peas have been an important protein source in Europe, especially around the Middle Ages, from when the following children’s rhyme came: “Pease porridge hot, Pease porridge cold, Pease porridge in the pot, Nine days old.”

There are two main varieties: smooth and wrinkly. Smooth makes for dried and split peas. Wrinkly has higher sugar content, and are usually eaten immature as a green vegetable.

Black-eyed pea/cowpea is not really a pea, but an African relative of the mung bean, brought to the southern US with the slave trade. It has a characteristic eye-like anthocyanin pigmentation around the hilum.

The pigeon pea is distant relative of the common bean. It is native to India. It has tough, reddish brown seed coat.

The “Grams” include several small seeded, quick-cooking beans. The green gram or mung beans are native to India, and widely grown in China. Grams also include the rice bean and the African bambara groundnut.

The azuki bean is an East Asian species of deep maroon color. It is mainly cultivated in Korea, China, and Japan. Azuki are a favorite sprouting seed, and are candied in Japan.

Lupins are mostly found in Italy. They are unusual because they contain no starch and 30-40% protein, 5-10% oil, and up to 50% soluble, but indigestible carbohydrates. They require special processing as many have toxic alkaloids. L. mutabilis is grown in the Andes and has a protein content approaching 50% of the dry seed weight.

Soybeans are the most versatile legume. Domesticated in China more than 3,000 years ago, the soybean spread widely as a staple food throughout Asia encouraged by the vegetarian doctrine of Buddhism. It only became known to the West until after the 19^th century. Today the US supplies half of the world production. However, most US soybeans feed livestock, not people, and much is processed for manufacturing purposes.