黄豆的“前世今生” - 2016年01月15日

Soybeans are a quintessential part of Chinese cuisine — from that glass of soymilk in the morning to spicy Mapo tofu, a perfect rice companion, at lunch. Tofu comes in a variety of tastes and textures, from soft to hard, from relatively bland to the "stinky" tofu that people seem to either hate or love.

Tofu is believed to have originated in Han Dynasty (206 BC- AD 220). Its popularity has spread beyond China's borders. Packed with protein and calcium, it's a favorite on vegetarian menus, a popular grilled topping for salads, and is even used to make specialty chocolate cake.

How tofu is made

There are three types of fresh tofu popularly sold in China: soft, firm and dried.

The traditional way of making tofu uses stone mills to grind the soybeans, then the mass is filtered through gauze to extract the milk, which is boiled.

"In olden times, people bought beans according to the season, but now they are available throughout the year," said Gao Xiaosheng, executive Chinese chef at the Pudong Shangri-La. "Although, it must be said that soybeans grown in greenhouses don't have the same savory, rich taste as those grown outdoors in the proper season."

A coagulant is added to the soymilk to form the curd. Chinese people traditionally use yanlu, or bittern, which is magnesium chloride, to make tofu. Some factory-made products use gypsum or other chemicals as coagulants. Gypsum is a soft sulfate mineral composed of calcium sulfate dehydrate.

Gao said current emphasis on food safety standards means that all coagulants must meet strict regulations.

"The most important step in making tofu is soaking the beans in clean water after sorting out the bad beans," he explained.

The beans have to soak overnight, even when machines are used.

"When I was young, my parents made their own tofu in the traditional way," Gao said.

Soft tofu, also known as silken tofu, is smooth and tender, with high moisture content. It is much more delicate than standard tofu. Soft tofu is commonly served as a cold dish with sauces and toppings like spring onions and preserved eggs, or in hot dishes like braised bean curd with crab meat and roe.

Soft tofu is also used in soups, such as the famous Wensi bean curd soup in Huaiyang cuisine. It requires the chef to have remarkable skills to cut the soft tofu into shreds almost as thin as hair.

The Wensi bean curd soup with sliced abalone that Gao makes at Gui Hua Lou is very silky, with a mild flavor that doesn't detract from the taste of the fresh tofu.

Firm tofu is made using gypsum as a coagulant. It is great in stir-fries and stews.

In Henan Province, firm tofu is prepared in the simplest way to preserve all the flavors of the soy. It is cooked in a steamer without cutting it into cubes or slices, and served with hot sauce and sesame sauce.

In the Chaoshan cuisine of Guangdong Province, Puning fried tofu is a popular snack. Tofu wedges are deep fried in hot oil and served with a dipping sauce made of leeks and chili peppers.

Dried tofu is produced by pressing most of the liquid out of the tofu. That renders it very firm.

"To make good quality dried tofu, the sieve must not have any holes to guarantee that every sheet is evenly formed," Gao said.

Dried tofu comes in different textures. Stronger varieties can be tied into knots and used in stews like braised pork, while some varieties are often used in stir-fries, cold dishes and hot pots.

In Yangzhou, there's the famous dish of stewed dried tofu shreds served in a high-quality soup stock.

"The dried tofu shreds used in this dish must have the right balance of tenacity and softness, and the soup is also very important," Gao said.

Tofu skin is a byproduct in the process of making tofu. Many people regard it as a nutritious delicacy. When boiling the soy milk in a big open pan, a skin of soy protein forms on top. That is collected and then dried into yellow-colored sheets.

"It's the essence of tofu," Gao explained. "The more skin you collect from boiling the soymilk, the greater is the chance that the tofu produced will break up more easily and lose flavor. There are factories that make only tofu skin and don't care much about the tofu itself. But I don't think those skins have that rich taste."

There are three main reasons when some tofu sold in markets doesn’t taste all that good: the water used to soak the beans wasn’t changed frequently in hot weather, the beans were ground too long or the production process wasn’t up to standards.

Fermented tofu

When tofu undergoes fermentation, two varieties are produced: doufuru, or fermented tofu, and "stinky" tofu.

Stinky tofu is a popular streetside snack. Its strong odor comes from fermentation in a special brine.

"Stinky" tofu is often fried and served with a hot sauce on top. Some people love it; some people don't.

In Jianshui County, Yunnan Province, the famous Jianshui grilled tofu is made with "stinky" tofu. The tofu cubes puff up when heated and are served with chili pepper, salt and ground pepper.

Fermented tofu comes in white, red and green varieties. Green fermented tofu is also stinky. The most popular brand is Wang Zhihe, which originated in the Qing Dynasty (1644-1912).

Fermented tofu is often eaten as a spread with steamed buns and flatbread. Red fermented tofu is also used to make sauces for stews and braised dishes, or stir-fried with water spinach.

Health tips

Though tofu is regarded as a very healthy food and an alternative protein source for vegetarians, there are still factors to keep in mind.

In summer, soft tofu with spring onions is a popular cold dishes, but eating raw tofu has its risks.

Gao said a restaurant in Tianjin that was known for its soft tofu with spring onions now makes its own tofu every day to ensure food safety after a food poisoning incident when tofu was purchased from a supplier.

"You must know how the tofu used in cold dishes is made, whether the quality is reliable and if the factory is certified," Gao said. "The tofu should be made the same day it is served."