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.

A note on hard beans

“Hard-seed” beans occur when temperatures are high, but humidity and water supply are low during the growing season. The outer seed coat gets very water-resistant. Hard-seed beans are smaller than normal and can be picked out before cooking.

“Hard-to-cook” beans are normal when harvested, but become resistant to softening when they are stored for a prolonged time (months) at warm temperatures in high humidity. This results from changes in the bean cell walls and interiors, including the denaturation of storage proteins and the formation of a water-resistant coating around the starch granules. There is no way to reverse these changes and no way of spotting them before cooking. Once cooked, they are smaller than normal and can be picked out.

Presoaking

Presoaking the dried beans in water can reduce the cooking time by more than 25%.

Heat penetrates a dry seed faster than water. If cooked directly from the dry state, much of the cooking time is spent waiting for water to get to the center. Meanwhile, the outer portions of the bean overcook and become fragile. Presoaking helps by allowing the water to reach the center first, before the heat cooks them.  

Soaking times depend on temperature. It is helpful to blanch the beans for 1.5 minutes in boiling water and then allowed to soak in the cooling water for two or three hours. Blanching rapidly hydrates the seed coat that controls water movement. If soaked in cool water, it takes 10-12 hrs before beans double in size.

Salt and baking soda speed cooking. Salt concentration at 1% (10g/l or 2 tsp/qt) speeds cooking greatly. Sodium displaces magnesium from the cell wall pectins and makes them more easily dissolved. Baking soda at 0.5% (1 tsp/qt) can reduce cooking time by 75%. It also contains sodium and its alkalinity facilitates the dissolving of cell-wall hemicelluloses. These additions, however, have an effect on the taste and texture of the cooked beans. Baking soda can give a slippery mouth feel and soapy taste. Salt reduces the swelling and gelation of starch granules within the beans, so the texture is mealy instead of creamy.

Cooking legumes

Fresh shell beans cook fairly quickly, in 10-30 min. Peas, lima beans, cranberry beans, and soybeans (edamame) are the legumes most commonly eaten fresh. Whole dried beans and peas take one to two hours to cook. Their larger size and water intake affect cooking time. Initially, water can only enter through the beans through the hilum, the little pore on the curved back of the bean. After 30-60 minutes, the seed coat has fully hydrated and expanded so that water flowing can pass across the entire seed coat surface, though the rate of flow is still limited.

The liquid in which legumes are cooked greatly affects both, the quality of the cooked beans and the time it takes to cook them. The greater the volume of cooking water, the more color, flavor, and nutrients are leached out of the beans, and the more they are diluted. Beans are best cooked in just enough water to soak up and to cook in.

Take into account the following:

• Boiling water speeds cooking, but damages seed coats and cause the beans to disintegrate.
• Temperatures below boiling (180-200 degrees F/80-93 degrees C) are gentler and better maintain bean structure.  
• Hard water with high levels of calcium or magnesium reinforces the bean cell walls, so cooking takes longer and may prevent the beans from softening fully.
• Acidity slows the dissolving of the cell wall pectins and hemicelluloses, so it slows the softening process but it helps maintain structure.
• Alkalinity does the reverse; it enhances the softening process.
• Sugar reinforces cell-wall structure and slows the swelling of the starch granules. It also helps maintain structure.
• Salt in the water slows the rate at which the beans absorb water, but it does get absorbed eventually. If beans are pre-soaked in salted water, they cook much faster.
• High altitude lowers the boiling point, so cooking dry beans is prolonged.

Note: ingredients such as molasses, which are somewhat acidic and rich in sugar and calcium, and acidic tomatoes can preserve bean structure during long cooking and reheating, such as in baked beans.

Legumes and flatulence

Many legumes contain large amounts of indigestible carbohydrates, such as oligosaccharides and cell-wall cements. The human body cannot break down these carbohydrates; therefore, they pass through the stomach in their complex form. Resident, symbiotic bacteria in the intestine break them down into absorbable forms. The increased growth and metabolism of the intestinal bacteria cause a sudden increase in gas production. 

Cooks can help minimize flatulence by manipulating legumes before consumption. Prolonged cooking helps break down much of the oligosaccharides and cell-wall cements into digestible single sugars. Oligosaccharides are also broken down during germination and fermentation, so sprouts, miso, soy sauce, and extracts like bean curd are less offensive than whole beans.

Legume structure and composition

Legume seeds consist of an embryonic plant surrounded by a protective seed coat. The embryo is made up of two large storage leaves, the cotyledons, and a tiny stem. The cotyledons are a transformed endosperm that provide the bulk of nourishment. The seed coat is interrupted at the hilum, a small depression where the seed is attached to the pod. It is through the hilum that the legume absorbs water.

Most beans and peas are mainly protein and starch, except soybeans and peanuts which have large contents of oil (between 25% and 50% respectively).

The colors of beans and peas are determined mainly by anthocyanin pigments in the seed coat. Solid reds and blacks survive cooking, while mottled patterns become washed out when their pigments leak into adjacent non-pigmented areas and into the cooking water. Color intensity is best preserved by cooking the beans in just enough water to keep them covered. It is best to add water only as needed to keep them barely covered.

Importance of legumes

Legumes have a high content of protein, two to three times that of wheat and rice. Their protein develops from a symbiotic relationship with species of the Rhizobium bacteria, which invade the roots of legume plants and convert nitrogen in the air into a form that is directly usable by the plant to make amino acids.

As a vegetable source of protein, legumes have been highly prized throughout history. No other food item has been so notably honored. Each of the four major legumes known to Rome lent its name to a prominent Roman family: Fabius (fava bean), Lentulus (lentil), Piso (pea), and Cicero (chick pea).

Legumes have been domesticated for thousands of years. Some date back to 3000 BCE. Today they make up staple ingredients in many food cultures.