What is stinky tofu made of?

In China's traditional cuisine, stinky tofu is undoubtedly a wonderful existence. That smell is enough to keep people who don't like it away; For those who like stinky tofu, it is the most delicious thing in the world.

That unique flavor, coupled with the frequent scandals in recent years, many people ask: what is this stinky tofu? Is it safe to eat?

First, stinky tofu is a fermented food.

In different areas, stinky tofu is made, processed and eaten in different ways, which can be roughly divided into two categories:

1, stinky tofu milk

That is, canned stinky tofu milk that can be bought in supermarkets.

It is made from tofu by natural fermentation to grow mold, and then pickled with salt and spices.

This stinky tofu is blue. It is said that it is famous for being loved by Empress Dowager Cixi and being named "Fang Yuqing". It is also eaten in the same way as ordinary tofu, for example, it is used to wrap steamed bread and pie, or as a snack with porridge.

2. Stinky tofu

The stinky tofu in the south is often not eaten directly, but is further cooked as ingredients, such as frying, charcoal roasting and steaming. This stinky tofu is easier to make than stinky tofu milk. Just soak the tofu in stinky salt water.

The fried stinky tofu often seen in snack street is made of this type of stinky tofu.

Either way, the core is tofu fermentation. Tofu is naturally fermented, mainly with mold; Dried bean curd is fermented with smelly salt water, and the strain is more complicated.

Second, why "smells bad and tastes good"?

"Smells bad and tastes good" is the unique feature of stinky tofu. This is not the exaggeration of fans, but has sufficient scientific basis.

Smell and taste are two different sensory experiences.

Smell is a process in which volatile small molecules enter through the nasal cavity and are perceived by olfactory cells. "Taste" is a comprehensive experience that food is perceived by taste bud cells when it is chewed in the mouth, while volatile molecules enter the nasal cavity from the mouth and are perceived by olfactory cells.

When we experience food, the molecules we "smell" and the molecules we "taste" are often different.

During the fermentation of stinky tofu, a part of protein of tofu is decomposed by complex microorganisms, and substances such as ammonia and sulfur-containing compounds are generated, which are the main sources of "odor"-yes, excrement is also rich in such substances. In addition, a large number of other kinds of volatile molecules, such as ethers, alcohols and esters, will be produced during the fermentation process, which constitutes the unique smell of stinky tofu.

At the same time, protease produced by microorganisms will also hydrolyze protein into peptides and amino acids, and these fermentation products have a strong fragrance. The most typical one is that glutamic acid is the effective component of monosodium glutamate and chicken essence, and all kinds of fermented bean products have strong fragrance, which is the mystery.

After cooking, especially frying and barbecue, on the one hand, those "odor molecules" volatilize fully and the smell is not strong; On the other hand, glutamic acid and other amino acids have outstanding umami flavor, and the Maillard reaction of amino acids at high temperature will further generate various flavor molecules, so it will be delicious to eat.

Third, "smelly brine" does have potential safety hazards.

In the production of stinky tofu, the key is the "stinky brine" used for soaking.

Different manufacturers make stinky brine in different ways. Some of them leave rice straw and meat in the open air for several months, allowing them to rot and ferment to obtain fermentation broth containing various microorganisms. Some people use Erythrina leaves, wild amaranth, bamboo shoots, Chinese cabbage, wax gourd, ginger, pepper and other plants to ferment, and it will take eight months or even longer to get qualified stinky brine without putting meat.

These traditional methods of making stinky brine can't control the kinds of microorganisms in it. Although "friendly microorganisms" needed for fermentation can be obtained, pathogenic microorganisms harmful to health cannot be excluded. In addition, many small workshops use inferior raw materials and sewage to make stinky brine, and the hygiene is even more uncertain.

In contrast, modern production can monitor the quality of stinky brine to a certain extent, such as monitoring the number of pathogenic bacteria. The stinky tofu made in this way is much safer.

4. Are "feces" and "chemical substances" stinky tofu true?

On the Internet, you will see some reports that stinky tofu is made of "dung water" or "chemicals".

From a technical point of view, it is impossible to make stinky tofu that smells bad and tastes good simply by using manure or chemicals.

However, it cannot be ruled out that the stinky tofu made by some unscrupulous traders has some flavor defects, such as the brine of stinky tofu is not smelly enough or the color is not deep enough, so they try to "optimize" it by adding manure or chemical reagents. Or some unscrupulous traders just heard that someone was doing it and did it.

5. Can stinky tofu still be eaten?

As a fermented bean product, stinky tofu is produced in a standardized way and is safe to eat. In the process of fermentation, the metabolism of bacteria will also produce some vitamins, such as vitamin B 12, which is easily lacking by vegetarians, and its nutritional value is even higher than that of tofu.

It should be noted that stinky tofu, like other traditional foods, has no uniform flavor standard or production technology-this diversity makes it difficult for people to objectively judge whether its flavor is good or not and whether it is safe and hygienic.

For diners who like to eat stinky tofu, it is undoubtedly more reliable to buy products from large enterprises with clear sources and under the supervision of the government than roadside stalls with unknown sources.

Author: Yun Orfila, Ph.D., Department of Agriculture and Biology, Purdue University, USA; Editor: Li Huai.