Course:FNH200/Projects/2020/Tofu

Introduction

Originated from China, tofu is a food that many people, especially Asians, have been enjoying. There are a lot of different tofu dishes from different parts of Asia such as China, Japanese, Korea and Indonesia. It has also gained its popularity in other parts of the world due to the various health benefits that it offers. Tofu is a good source of protein, making it a suitable substitute of meat for vegans. It also contains fibre as well as a variety of minerals such as potassium, magnesium, iron, copper and manganese. Tofu is made of soybeans that are soaked in water, heated and coagulated with calcium or magnesium salt, and the resulting curd is then pressed into blocks. There are different types of tofu which are extra-firm tofu, firm tofu, soft tofu and silken tofu, depending on its softness.

History of Tofu

Tofu was first discovered about 2,000 years ago in China. However, there are different theories regarding the origin of tofu such as the Liu An theory, Accidental Coagulation theory, Indian Import theory, and Mongolian Import theory. The Liu An theory states that tofu was invented by Liu An, a Han Dynasty prince. The Accidental Coagulation theory states that tofu was invented by accident around AD 600 in Northern part of China. The Indian Import theory states that tofu was imported from India by the dairying tribes or Buddhist monks. The Mongolian Import theory states that the idea of tofu innovation was modified from cheese making process which came from milk-drink Mongolian tribes that lived in Northern border of China.

Processing

Processing of soybeans

The first step in the production of tofu is soaking the soybeans. Soaking helps to accelerate the extraction of protein from the beans, which creates tofu with better protein content. In some cases, removal of soybean hulls happens first before soaking, which helps to make the colour and taste of tofu more appealing. The protein content and texture of tofu can also be improved by freezing the soaked soybeans or by using sprouted soybeans in the production process.

Afterwards, soaked soybeans are ground to form a slurry. This soybean slurry can be treated in three different ways before being filtrated to obtain soy milk: without cooking, with cooking or hot water mixing. During filtration, soy milk is separated from the soy pulp (okara), generating soy milk with 10% to 22% solid content.

Coagulation of soy milk

Soy curds formed after coagulation

After filtration, the soy milk is coagulated to solidify the protein and oil present in it. There are three different types of coagulants commonly used in tofu production: salts, acids and enzymes. These coagulants can be used by themselves or in combination with one another.

Salt coagulants

Calcium sulfate is the most commonly used salt coagulant in tofu production, which also creates the unique aroma and taste of tofu. Another type of salt coagulant is nigari, which consists of magnesium chloride combined with calcium chloride. Since nigari is produced by removing sodium chloride and evaporating seawater, its contents can vary depending on the components of seawater used, which may be difficult to use in standardized large-scale tofu production.

Acid coagulants

Edible acids like glucono delta-lactone (GDL) are used as coagulant in the production of soft or silken tofu, as it creates a softer tofu texture in a shorter time. This allows silken or soft tofu to be produced directly in its container, reducing the formation of air gaps such that they can be transported without breaking. Calcium sulfate is often used together with GDL to minimize the sour taste of the final product.

Enzyme coagulants

Enzymes such as papain and proteases can be used as a coagulant as it helps to catalyze cross-linking between amino acids in the proteins.

Pressing and packaging of tofu

Tofu pressing is especially important in the production of firmer tofu as it squeezes excess liquid out of the soy curd. It is often done with a hydraulic press, where the soy curd is pressed with varying weights to reach the desirable firmness. The heavier the weight used, the firmer the tofu will be. Afterwards, the pressed tofu is cut into desired sizes and packaged. Pasteurization or UHT (ultra high temperature) technology and aseptic packaging are often used to increase the shelf life of tofu.

Silken or soft tofu production does not involve pressing, as the coagulation process happens directly inside the packaging with the help of water bath to maintain the optimum temperature for the coagulants to work.

Varieties

Silken tofu

Varieties of Fresh Tofu can be divided into two big categories; silken and regular tofu. Fresh tofu is usually categorized further by its firmness. It is based on how much water is pressed out of the tofu; the more is pressed out, the firmer it gets while simultaneously increasing its protein and fat content.

Silken Tofu

The type of tofu with the highest water content with a custard-like texture. Silken’s tofu consistency depends on the amount of soy it contains. Its texture made silken tofu a perfect substitute for almost everything from soy milk to cream. It is used in a lot of vegan recipes as a substitute for eggs and dairy products. Silken tofu is usually labeled as soft, firm, or extra firm; however, the difference is minimal.

Soft tofu

Regular tofu

Regular tofu or non-silken tofu is pressed tofu with a sponge-like texture. It comes in varieties from soft tofu up to super firm tofu; the more firm the tofu, the denser it gets and has lower moisture. The more solid the tofu, the harder it is to infuse flavour to the tofu, which is a crucial consideration in choosing what tofu to use.

Soft tofu

This is the Chinese equivalent of silken tofu with similar properties, making it used in similar ways when cooked. However, compared to silken tofu, it is less smooth.

Medium tofu

Firm tofu

Denser than soft tofu but still have a delicate texture. Used in soups such as miso or frequently served cold.

Firm tofu

Normally stir-fried or pan friend, this kind of tofu absorbs flavours well. How well firm tofu hold its structure is based on the brand and its production. Firm tofu may also be scrambled in food and substitute to ricotta cheese in vegan recipes.

Extra-firm tofu

This kind of tofu holds its shape very well, making it great to cut, slice, cube, all kinds of frying, baking, and grilling as it won’t easily crumble down like the softer tofus when being cooked. In vegan dishes, it is sometimes used as a substitute for ground meat by crumbling it down before cooking.

Extra firm tofu

Super firm tofu

This kind of tofu is very dense with high protein content. Excellent when it is cooking in a hurry as it would not fall apart, and there is less water to cook. However, because of its low moisture, it dries out fast when baked or grilled high heat.

Tofu dishes

Indonesia

Tofu has been a staple in Indonesian dishes for many many years now. Almost every region and province in Indonesia has their own tofu dish. They are often fried, sautéed, poached, and many more.

Here are some examples of tofu dishes in Indonesia:

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  Gulai tempe dan tahu: fried tofu slathered in Indonesian curry (gulai), usually eaten with tempeh.

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  Tahu bacem: tofu slowly simmered in traditional Indonesian spices

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  Tahu kecap: tofu dish that has different versions in each province of Indonesia. It is generally tofu sautéed with sweet soy sauce and often chili.

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  Tahu isi: tofu stuffed usually with vegetables and sometimes meat.

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  Mun tahu: tofu dish served in a thick sauce, usually eaten with meat such as shrimp and minced beef.

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  Ketoprak: tofu dish that is mixed in a peanut sauce, usually served with rice noodles. This dish also has different versions that vary from province to province.

China

Some would say that tofu in China is synonymous to pasta in Italy. It plays a really important role in Chinese culture and diet.

Here are some examples of Chinese tofu dishes:

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  Mapo tofu: traditional Chinese tofu dish served spicy with minced meat. Usually eaten with rice.

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  Pidan doufu: tofu served with thousand year old egg.

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  General Tso's tofu: tofu dish that has been westernized, but it actually originates from the Zou province of China.

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  Almond tofu: tofu served as a dessert, usually also made with almond milk and agar.

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  Stinky tofu: tofu that has been fermented for a long time and has a distinct smell.

Japan

Tofu in Japan has also been especially popular and important. Here are some dishes served in Japan:

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  Agedashi tofu: fried tofu in tsuyu sauce, often topped with bonito flakes that is often served as an appetizer

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  Yudofu: tofu in a dashi kombu.

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  Tofu donburi: tofu served over rice, usually with seafood and other types of meat sautéed with vegetables.

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  Miso soup: tofu is usually served in miso soup, which is a fermented soybean-based soup.

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  Tofu curry don: deep fried tofu with breadcrumb batter, slathered in Japanese curry sauce.

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  Inari sushi: seasoned rice wrapped in a sweet marinated tofu skin

South Korea

South Korea also has many tofu dishes. They are mostly eaten as sides, but has many main dishes that use tofu as the star of the show. Here are some dishes:

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  Dubu Jorim: braised tofu dish, served with Korean spicy sauce

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  Jjigae: Tofu is often served in Korean stews, which also contains other vegetables, meat and sometimes kimchi.

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  Kongbiji jjigae: soft and creamy tofu dish that is made from the leftover pulp of making tofu, usually eaten with pork ribs or beef.

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  Dubu gui: a simple Korean tofu dish, the tofu is pan-fried and eaten with different types of sauce

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  Sundubu jjigae: another type of Korean stew, made with soft or silken tofu

Potential Final Exam Question

What thermal preservation method is commonly used in the processing of tofu?

A. UHT

B. Pasteurization

C. Commercial sterilization

D. A and B only

E. All of the above

Explanation:

After firm tofu is pressed and cut, it will then be packaged in individual packagings. In order to increase the shelf life of tofu, packaged tofu is usually pasteurized at about 180°F (82°C).

Ultra-high temperature (UHT) processing can also be used in which the soy milk is heated to a temperature between 60°C and 105°C, deaerated and homogenized in order to create aseptic soy milk. This aseptic soy milk will then be coagulated, pressed and packaged in aseptic packaging.