Course:FNH200/Projects/2025/Soybeans: Small Beans, Big Impact

Introduction & History

Tofu

Tofu, a staple of East Asian cuisine, traces its origins to soybean domestication in China, later spreading to Japan and Korea. The method of curdling soy milk and pressing the curds into blocks emerged during the Han dynasty (206 BC–220 AD). By the Tang and Song dynasties, tofu had spread across East Asia, becoming integral to Buddhist vegetarian diets.

Culturally, tofu is more than food, but it is identity. In China, it is called “vegetable meat” for its role as a protein-rich meat substitute. In Korea, fermented soy products like 'doenjang' and 'cheonggukjang', recorded as early as the 3rd century AD, highlight soy’s deep culinary roots. Folklore often uses tofu as a metaphor for modesty and kindness.

Nutritionally, tofu is a complete plant protein containing all nine essential amino acids. It is rich in calcium, iron, magnesium, and potassium, and its isoflavones are linked to better bone health, cardiovascular benefits, and reduced cancer risk. Eating tofu once a week has been associated with an 18% lower risk of heart disease.

In Canada, soy is classified as a priority food allergen and must be clearly declared on labels for prepackaged foods, either in the ingredient list or in a “Contains: soy” statement. The Canadian Food Inspection Agency (CFIA) enforces these rules under the Food and Drugs Act and the Safe Food for Canadians Act, with penalties for non-compliance including product recalls.

Processing & Fermentation

In the factory, soybeans undergo a series of processing steps from raw materials to soy milk, then to curdling and pressing to form tofu. The tofu is cut into pieces and left to ferment for several months, eventually resulting in fermented tofu.

Soybean to Soy Milk

The first stage in tofu production involves processing raw soybeans into soy milk. The soybeans are cleaned to remove impurities such as dust, stones, and damaged seeds, and then soaked in water for several hours to soften their texture and facilitate grinding. After soaking, the soybeans are drained, rinsed, and ground with water to form a paste, which is then mixed with water and ground again to make soy milk. And then cooked to inactivate enzymes, improve flavour, and aid protein extraction. The cooked slurry is filtered to separate the liquid soy milk from the solid residue, known as okara. The quality of soy milk is influenced by factors such as the soaking time and temperature, the bean-to-water ratio during grinding, and the efficiency of filtration. Optimizing these parameters can enhance protein yield, improve flavour, and produce a smooth, uniform soy milk suitable for coagulation in the next stage of tofu production.

tofu processing to add coagulation

Soy Milk to Tofu

After previous steps, cool the filtered soy milk to about 80 °C, then add the coagulant while stirring gently. Allow the mixture to rest undisturbed to achieve full coagulation. Once set, break the curd, carefully transfer it into a mold, and press it using an automatic press. The pressed curd is then released from the mold, yielding the finished tofu.

Adding a coagulant is one of the important steps in converting soy milk into tofu curd. Coagulants can be salt, acid or enzymes. Among the most commonly used coagulants are calcium sulfate, nigari (NGR), magnesium chloride and glucose acid-δ-lactone (GDL). Adding these substances can result in a satisfactory texture of tofu. The types and concentrations of the coagulants play a crucial role in the formation of the internal network structure of tofu. Besides the thermal processing methods such as filtration boiling method (FBM), boiling filtration method (BFM), and repeated boiling filtration method (RBFM), modern non-thermal technologies such as ultra-high pressure homogenization, cold atmospheric plasma, plasma-activated water, and high static water pressure have been widely applied in tofu processing.

Tofu

After being molded and pressed, the tofu has completely taken shape, forming a large block of tofu. Then it is cut into pieces, soaked in water, and packaged for sale.

Soybean yellow whey (SYW) is a yellow liquid by-product obtained during the process of making tofu through pressing, or it is formed when soy protein reacts with a coagulant. Fresh soy whey was fermented with multiple strains to produce fermented yellow whey (FYW) rich in organic acids (lactic acid, acetic acid, citric acid, etc.) and probiotics (lactic acid bacteria, acetic acid bacteria, etc.). By adjusting the pH of soy milk to the isoelectric point of soy protein, FYW forms a gel and is used as a natural coagulant recycled in the process of making tofu. By using the optimized boiling filtration method (ideal parameters: bean-water ratio 1:5, boiling temperature 105°C, boiling time approximately 6 minutes, and 26% FYW), the yield and protein content of tofu can be significantly increased, which is nearly 48 grams/100 grams higher than that of the standard method and 4.16% higher in protein content.

The tofu products made with FYW have high nutritional value, good hardness, excellent water retention ability and unique flavour. Soy yellow whey is also the waste material containing nitrogen and nutrients that remains after the production of tofu. Its fermentation application can reduce the generation of waste and thereby achieve increased production and efficiency.

Fermented Tofu

process for fermented furu

The tofu is then cut into even smaller pieces. After one round of fermentation, it becomes mao tofu or hairy tofu. And after a second round of fermentation, it can be transformed into furu.

mao or hairy tofu:

The production of mao tofu begins with inoculating soybeans with Mucor moulds. After 3-4 days of cultivation, these moulds will form a distinctive layer of white mycelium. Lactobacillus and Trichosporon are the most important strains throughout the fermentation process. As the fermentation progresses, the bacterial diversity increases while the fungal diversity gradually decreases. The physical and chemical changes include a decrease in moisture and pH, an increase in hardness, viscosity and chewiness, as well as the production of delicate umami flavours from proteins, peptides and free amino acids.

furu:

To make furu, the moldy sections of the bean curd blocks are placed in a brine made with salt, rice wine, spices or various seasonings for secondary fermentation (3 to 6 months) to form different flavours of furu. During the maturation process, the action of microorganisms and enzymes will further break down the bean curd, making its flavour, aroma and nutritional value more abundant. Mucor proteases can remove or reduce the bitterness of the fermented tofu, and the Mucor fungus can also secrete a catechol oxidase, making the fermented tofu present an attractive golden colour and stimulating appetite.

Preservation

Koya-dofu (frozen-dried)

Tofu has been preserved for centuries using non-fermentative methods that limit microbial growth and moisture. Traditionally, techniques included smoking, storing in salted brine, freezing, and freeze-drying. Tofu was frozen outdoors and then dried to make kori-dōfu / kōya-dōfu. Freezing creates large ice crystals that, upon sublimation/drying, leave a porous, low-moisture matrix that resists microbial growth and rehydrates quickly during cooking. Government-affiliated research (JIRCAS/JARQ) documents the classical sequence: freezing → ageing → thawing → seasoning → drying, and its modernization into controlled, continuous freezing for consistent quality. Contemporary studies on frozen or vacuum-sealed frozen tofu further show that freeze-thaw treatments alter water distribution and texture while extending storage stability when held at -20 °C. Modern preservation builds on these principles with improved control over temperature, packaging, and sanitation. Vacuum-sealing and pasteurization are commonly used to extend refrigerated shelf life, while aseptic packaging allows silken tofu to be stored unrefrigerated for months.

Another long-standing approach is drying and brining of pressed tofu (e.g., dried/marinated “dougan” styles). Drying lowers water activity, while salt and acid in brines suppress spoilage organisms and oxidative changes; recent work on leisure dried tofu shows marination reduces total viable counts and stabilizes texture during storage. Storage studies on dried tofu products also describe quality limits driven by lipid oxidation and textural hardening, underscoring why moisture and oxygen control remain critical.

Across both traditional and modern methods, the throughline is water activity reduction, temperature control, and exclusion of oxygen and contaminants, the very preservation mechanisms we have already linked to in the processing and fermentation sections.

Conclusion

From its origins in ancient China to its place in modern kitchens worldwide, tofu has stood the test of time as both a cultural symbol and a nutritional powerhouse. What began as a simple method of curdling soy milk has evolved into a diverse array of products, from fresh silken blocks to richly flavored fermented varieties like mao tofu and furu. These transformations showcase not only the creativity of culinary traditions, but also the role of science in refining texture, taste, and shelf life. Modern processing techniques and innovations, such as fermented yellow whey, have improved efficiency, reduced waste, and enhanced tofu’s nutritional value—demonstrating how tradition and technology can work hand in hand. Beyond its health benefits, tofu carries deep cultural meaning, serving as a staple in vegetarian diets, a metaphor in folklore, and a bridge between generations. In many ways, tofu’s story is more than just about food—it’s about adaptability, sustainability, and the enduring power of simple ingredients to shape history and connect communities.

Question

Question

In Mao Tofu (“hairy tofu”) fermentation, which option correctly matches the dominant microbes to their primary roles? (no more than one correct answer choose all that apply)

A. Mucor - forms white surface mycelium; secretes enzymes that reduce bitterness and contribute color/flavor;

B. Lactobacillus - produces lactic acid, lowers pH and aids preservation;

C. Trichosporon - proteolysis releasing peptides/amino acids that boost umami.

D. Penicillium camemberti - surface mycelium;

E. Saccharomyces cerevisiae - ethanol production driving acidification;

F. Acetobacter - minor role in aroma only.

G. Clostridium botulinum - proteolysis at low pH.

Correct Answer

A, B, C

Explanation:

Links microbial fermentation to changes in tofu’s texture, flavour, and safety - key food science concepts in FNH 200.