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Fermented bean curd, also known as sufu, fermented tofu, skinky tofu, furu, nanru, or mildew tofu is a soft, spreadable, cheese-like condiment that originates from China. It is typically salty, known for its strong aroma, cheese-like consistency and either white, red or grey colour. A traditional Chinese dish, fermented bean curd is often served with steamed buns or breakfast rice. Fermented bean curd is typically cut into cubes and is packaged in a clear glass container and covered in brine to ensure a long shelf life.



Processing
There are several ways to process tofu to create fermented bean curd (also known as sufu). The four primary methods of processing include; 1) mould fermented; 2) naturally fermented; 3) bacteria fermented; and 4) enzymatically ripened. The first three methods involve four main steps including; 1) preparation of tofu, 2) preparation of pehtze, 3) salting and 4) ripening. These three methods differ by the fermentation technique used in the preparation of pehtze step. Mould fermentation and bacteria fermentation involve using a pure mould or bacterial culture to conduct the fermentation whereas natural fermentation does not involve the addition of anything before the salting and ripening phases. The fourth method (enzymatic ripening) does not require fermentation before ripening and therefore only requires step 1, 3 and 4 mentioned above. Processing traditionally occurred domestically but now occurs both on a commercial and household scale. A diagram of processing steps can be seen here:

Preparation of Tofu
Soybeans are soaked in water overnight, then ground into a slurry. The slurry is then diluted and pressed into soymilk. Calcium sulphate or magnesium sulphate is then added to the soymilk to precipitate out soy which is then pressed to remove access water to create soy whey. The result is a soft, but firm tofu.

Preparation of Pehtze
Pehtze, otherwise knowned as moulded tofu, are placed on wooden trays and surrounded by straw where they are left to inoculate and ferment naturally. Because the pehtze is left in a natural environment, which is not favourable in temperature for yeasts or other bacterias, Mucor spp. is typically the bacteria which contributes to fermentation. Fermentation typically occurs over 5 to 15 days. Before the pehtze is sent for salting, it is flattened in order to press the mycelium of the mould into a firm film on the sufu surface so that it keeps its shape throughout the rest of the processing steps.

Salting
Pehtze is transferred to jars, where salt is spread in between layers of the fermented tofu. Once salt content reaches approximately 16% (usually over 6-12 days), the pehtze is removed from the jars and rinsed with water.

Ripening
During the ripening phase, previously salted pehtze is layered in jars with a dressing mixture (brine) which is unique based on the location, climate and culture of the region where the fermented bean curd is made. Dressing mixtures are the main reason for different types, flavours and colours of sufu. Commonly, dressing mixtures include angkak, alcoholic beverage, salt, sugar, flour (or bean) paste, and spices. Once layered, the jars are sealed with bamboo leaves and clay. The jars are typically allowed to age for 6 months.

Preparation of Tofu
Preparation of tofu is similar to traditional methods, however steps are highly mechanized. In addition, 20% more coagulant (such as calcium sulphate or magnesium sulphate) is added to the soymilk to precipitate out desired contents. Again, large machines are responsible for pressing the water from the resulting precipitate (soy whey) in order to obtain the soft but firm tofu product.

Preparation of Pehtze
Instead of allowing pehtze to ferment naturally, pure culture moulds of the Mucor spp., Actinomucor spp., or Rhizopus spp variety are sprayed onto the surface of the tofu to initiate the fermentation process. Ideal conditions in temperature, humidity and cultivation time must be kept in consideration depending on the type of mould being used. If conditions do not favor the growth, fermentation times could be greatly delayed or inhibited all together.

Salting
Several ways of commercial salting can be used such as: 1) being transferred to containers and salted by layer; 2) being transferred to vessels with highly saturated salt solutions; or 3) being submerged in an alcoholic saline solution.

The first method is most similar to traditional salting methods, however, this method often requires more time to reach optimum salt concentrations. In addition, inconsistent salt concentrations throughout the pehtze can be a result of this method. The second method is widely used and takes approximately 4-5 days for the pehtze to reach optimal salt concentrations of over 12%.

The third method involves submerging the pehtze in a solution with 12% NaCl and 10% ethanol. The salting and ripening occur in this solution; therefore, the pehtze can be sold directly following this method of salting.

Ripening
Again, previously salted pehtze is mixed with a dressing according to the type of desired sufu and left to ripen. Commercial ripening, though quicker than traditional methods, still requires 2-3 months. Ripening is able to occur quickly because of lower salt and alcohol contents, more consistent and controlled ripening temperatures and the use of smaller jars. By lowering salt concentrations to quicken the ripening process, commercially process tofu has the challenge of a shorter shelf life. As a solution, a paraffin layer may be added to the surface of the pehtze to prevent spoilage. In addition, stem bromelain may be added to the tofu to speed up the ripening process."(There is a that in a fermented bean curd factory, however it's not in English.)"

Health and Nutrition
Naturally, soy beans are already high in proteins and lipids with different kinds of valuable minerals such as calcium, phosphorous and iron. However, they are also known to have low bioavailability. By fermenting tofu, larger molecules (peptides) break up into smaller molecules by hydrolysis, which makes the nutrients easier to digest. Fermented bean curd has shown to have anti-mutagenic and anti-oxidative properties which regular tofu does not. Every fermented bean curd varies in the strain of bacteria, addition of ingredients, spices, condiments, and different fermentation conditions (humidity and temperate which affect the overall benefits of fermented bean curds.

Isoflavones in fermented bean curd are enhanced through the fermentation process. They inhibit osteoporosis, cardiovascular diseases, and can alleviate women’s menopausal symptoms. Most importantly isoflavones are anti-mutagenic. In addition, red fermented bean curd shows 50% more anti-mutagenic activity compared to white fermented bean curd. Hot peppers, garlic, yellow rice wine and sesame oil are common ingredients in this type of fermented bean curd with higher anti-mutagenic activity.

Phenolic components contribute to the majority of the anti-oxidative properties of fermented bean curd. Also, tofu fermented with common ingredients such as rice malt, sesame oil, and chilies showed more anti-oxidative activities compared to regular, non fermented tofu.

Glycinin and β-conglycinin are also found in fermented soy products and have numerous health benefits such as anti-hypertensive, antimicrobial, antioxidant, anti-diabetic and anticancer properties.

There is also nutritional difference between the brine used for fermentation and the fermented bean curd itself. The brine shows anti-oxidative and anti- mutagenic properties but at lower levels then the fermented tofu.

Cultural Relevance
===Origin === Fermented bean curd originated in China, where the first documentation of it was in 1596 by Li Shizhen during the Ming Dynasty. Instructions on how to make tofu by heating soymilk was written. After heating the soy milk, he stated any film that forms on the surface should be taken and “dried to give yuba ”. He also mentioned the types of soybeans such as black and green as well as their uses.

Li Rihua in 1610 is the next to mention fermented bean curd. The process is described as taking off “the hair” of the tofu at which point it is then finished. The book states that "the hair" Rihua refers to describes fungal mycelium found on the surface of tofu during the fermentation process.

Frozen tofu is first mentioned by Shixian  hongmi in 1680 where the appearance is described and instructions on how to cook it are given. Making fermented tofu is also mentioned during this period, where it is stated to press all the water out of the tofu, cut it into squares and place it on bamboo steamer pads. Specific dates of when to cover the steamers and wait for the hairy growth are noted.

Hitsujun Ka in 1783 provides illustrations of a woman making fermented tofu and provides reference to Japan.

In 1878, Wells Fargo & Co were the makers of the earliest recorded commercial tofu product in the west and the first soy product in California. Another prevalent publication on soy in Europe was written by Auguste Paillieux in 1880. It was the biggest book on soya during that time.

In 1898 Nguyen Hanh Tran wrote a book on soybeans to describe how Europeans could use it. He described six different types of food made from the soybeans: tofu, pressed tofu, yuba, fermented tofu, chao and dau-hu-oa and gave instructions on how to make them.

A book review in the New York Tribune in 1902 gives the earliest mention of fermented tofu in English.

Yu-ying Li gave a speech at the 2nd International Dairy Congress in 1905. He discussed the use of milk from sources such as soy, as an alternative to animal milk because of the cost of raising cows in China. At the time vegetable milk made by "Soja hispida" seeds was used to make tofu. Li also listed the benefits of using soy over other products.

Current Use
Fermented bean curd usually is divided into three categories which are white (bai-fang), red (hong-fang) and grey (qing-fang). Since the fermented bean curd is cut into small cubes, the word "fang" (which means sharp square) is used as its trivial name. In China, fermented bean curd can be utilized as a soybean cheese which is recognized as vegetarian cheese as well. In Japan, it is also named Tofuyo (豆腐ょぅ). White fermented bean curd maintains the original color of tofu which is the same as the original soybean color. The red variety gets its red color by adding red yeast rice and sorghum wine during fermentation. The grey variety, also known as stinky tofu, emits a pungent odor and appears iron blue in color. Though each type of fermented bean curd has an unique flavor, they can all be matched with a wide variety of foods, mainly starchy side dishes like bread and rice. To enhance flavor, ingredients such as sesame oil, chili oil or rose wine may be added to the fermented bean curd.

White fermented bean curd
The white fermented bean curd (Chinese: 腐乳/白方,pinyin: furu)is widely used in Asian cuisines especially in southern China. Compared to the other two types of fermented bean curd, white fermented bean curd has the lightest flavor. Therefore, it is considered as a prefect match for plain rice porridge as salt. It is one of the traditional ingredients in Cantonese cuisine. The most famous dish is

Red fermented bean curd
The red fermented bean curd (Chinese: 南乳/紅方,pinyin: nanru) is more salty in flavor than white fermented bean curd. It contains a strong bouquet from the red yeast rice and sorghum wine and can be distinguished from other two types of fermented bean curd by its aroma and bright red colour. A traditional dish of Chinese lunar new year's dinner is. Currently, the red fermented bean curd is not only utilized on traditional cuisine and also combined with Western style as a special type of ingredient such as which is used as a BBQ sauce.

Grey fermented bean curd
The grey fermented bean curd is also called fermented stinky tofu or fermented stinky sufu (Chinese: 臭豆腐乳,霉豆腐/青方, pinyin:choudou furu) or mildewed tofu. The most famous grey fermented tofu is in Beijing, China and the stinky smell is consider a symbolic icon for the grey fermented bean curd. To create grey fermented bean curd, the tofu it is added to a unique stinky brine from vegetable or seafood ingredients, which allows it to become mildewed and absorb a stinky odor. The traditional way of eating is to mash it onto a steamed bud, similar to cheese on the burger. It is also considered a perfect dipping ingredient for Chinese Hotpot in Beijing, China.

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