How Tofu Is Processed

Methods to produce various types of tofu will be described, as will effects of processing on the final product properties of this healthy food.

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Tofu originated in China. It is thought to have been developed first by Liu An, a Han Dynasty prince who lived during the second century B.C. During the 1960s, the Japanese Food Research Institute recommended modernizing and standardizing tofu production throughout Japan. This effort led to significant advances in tofu processing. Although tofu has been made in the United States since the beginning of the 20th century, its consumption didn’t increase rapidly until around 1970.

Today, the United States is one of the largest producers of soybeans in the world. Yet tofu is consumed at relatively low levels in the United States compared with other countries. Tofu sales during 2014 were $274 million in the United States, according to the SoyFoods Association of North America. Tofu is largely consumed as an ethnic food or as a high protein, vegetarian alternative to meat and cheese. Tofu can also be found in a variety of other foods including hot dogs, burgers, ice cream, sauces, desserts, and shakes.

There are numerous types of tofu, including extra firm, firm, soft, and silken tofu. Extra firm and firm tofu have textures similar to cooked meat and raw meat, respectively. Their rigidity lends them to use in stir-fry dishes, grilling, and soups. Soft and silken tofu are fragile and have soft and silky textures. Soft and silken tofu can be blended into sauces or used as desserts or drinks. Other types of tofu include fermented tofu, flavored tofu, fried tofu, and frozen tofu.

Nutritionally, tofu is cholesterol free, low in saturated fat, and high in protein. On a moisture-free basis, tofu contains about 50% protein and 27% fat, most of which is polyunsaturated fatty acids. Tofu is also a good source of calcium. The U.S. Food and Drug Administration approved a soy health claim in 1999, and tofu has been shown to have numerous health benefits (Rekha and Vijayalakshmi 2013).

Tofu Processing - Step 1

Soaking, Grinding and Cooking the Soybeans

Tofu production begins with soaking and grinding the soybeans. Soybeans can be soaked anywhere from 9 to 10 hours at lower temperatures (22°C) or 4 to 6 hours at higher temperatures (32°C). If the beans are ground prior to soaking, the soaking time can be reduced. In some cases, soybean hulls are removed prior to grinding. Dehullers use soft, rotating rubber rollers to remove the hulls. This improves the color and reduces the beany flavor of the final tofu (Kang et al. 2014). In addition, soybeans can be pretreated with sodium bicarbonate to decrease beany flavor and increase smoothness of the final tofu (Rekha and Vijayalakshmi 2013). Grinding can be performed using a variety of types of equipment, including micro-cutters, hammer mills, and other similar devices. The more thoroughly ground the slurry, the more protein extracted and the better the yield. Next the ground slurry is cooked, typically to 100°C to 110°C for 3–10 min. This process denatures the soy protein and removes volatile beany flavors.

Tofu Processing - Step 2

Separating the Soy Milk

Then the soy milk needs to be separated from the solid soy pulp or fiber, also known as okara. This can be done through centrifugation and/or filtration. Alternately, the soy milk can be separated from the okara prior to heating. In some cases, the soy milk is concentrated prior to coagulation. This can be performed though a variety of processes, including heat, reverse osmosis, vacuum evaporation, or nanofiltration. The texture of the final tofu depends largely on the solid content of the soy milk prior to coagulation. Soy milk can be concentrated to between 10% and 22% solids (Kang et al. 2014).

Tofu Processing - Step 3

Coagulating the Soy Milk

The coagulation step is the most important step in the manufacture of tofu. Its purpose is to coagulate the protein and oil in the soy milk. Different coagulants are used to produce different types of tofu. The three main categories of coagulants that are commonly used are salts, acids, and enzymes. They can be used alone or in combination. Coagulants are typically added at concentrations between 1.5 and 5.0 g/kg while stirring the soy milk at temperatures between 60°C and 90°C. Stirring the milk for the first 5 seconds of coagulation improves yields (Rekha and Vijayalakshmi 2013).

Reference

McHugh, T. (n.d.). How tofu is processed. IFT.org. https://www.ift.org/news-and publications

Kang, C. S. et al. 2014. Tofu Manufacturing Process. U.S. Patent Application 20140302199 A1.

Onodera, Y. et al. 2009. “Homogeneity and Microstructure of Tofu Depends on 11S/7S Globulin Ratio in Soymilk and Coagulant Concentration.” Food Sci. Tech. Res. 15(3): 265–274.

Rekha, C. R. and G. Vijayalakshmi. 2011. “Influence of Processing Parameters on the Quality of Soycurd (Tofu).” J. Food Sci. Technol. 50(1): 176–180.