Course:FNH200/2012w Team09 Tofu

Introduction

What is Tofu?

Japanese Silken Tofu [1]

Tofu is a custard-like product made from soybeans and it is an important source of protein in Asian cuisine. It can also be called bean curd and is often described as being cheese-like. It is high in protein and often used as a meat substitute for vegetarian cuisine, thus illustrating how it has become popular enough to not only be a staple food in Asia, but in Western culture as well. Furthermore, there are two types of tofu: silken (or soft) tofu and firm (or regular) tofu, which are cooked differently.

How did tofu get its name?

According to William Shurtleff and Akiko Aoyagi, tofu in Mandarin is written as 'doufu'. Interestingly, tofu is actually a Japanese word, and though it is used worldwide and in Japan, articles coming from China called it “bean curd” or “soybean cheese”.

Nowadays, popular culture has readily accepted tofu and its uses vary from being fried, to being used as pizza toppings, sandwich fillers, and even in desserts.

Questions to think about...

Due to its nutritional value and its role as an alternative in the constitution of a meal, many have found tofu very appealing and quite tasty too. Due to our curiosity about tofu preservation and how different preservation methods can affect the tofu, that has brought this page to be. As you will see, different tofu preservation methods affect the final product significantly. Different methods include, frozen, freeze-drying, deep frying, pasteurization, fermentation, and the use of preservatives. Consequently, here are a few questions to keep in mind while reading the rest of this text:

1) Coagulants are a type of additive. We mentioned different types of coagulants applied in tofu making, what are the functions of these coagulants? Are certain coagulants favoured over others?

2) There are several kinds of tofu products in the markets, could you describe the ways of preservation methods in some tofu products?

3) Which method do you consider to be the safest (or best) to effectively preserve tofu? How much does the intended shelf-life of tofu influence your choice?

4) Does the video ease your understanding of preservation methods by enabling you to see a visual representation?

5) Do the benefits and disadvantages of tofu influence your consumption of the product? Why?

History: Tofu Discovery in Different Parts of the World

China

Tofu was first introduced as a common food in lower class people during the Sung Dynasty. This soon escalated in the Ming Dynasty when tofu became a popular food amongst both the rich and the poor. Within the different types of tofu, firm tofu and fermented tofu, which are both unique to Chinese origin, were the most popular. The most common preservation methods used by the Chinese to achieve these types of tofu included: 1) Pressing tofu to reduce the moisture content 2) Deep- frying tofu 3) Dipping tofu into soy sauce or spicy sauces as salt and spices can act as antimicrobial agents 4) Fermentation by preserving the tofu in a salt or alcohol mixture

Japan

Tofu was first introduced to the upperclassmen of Japan from China. However, tofu was often used as a ritual offering instead of being eaten as a food. It was only around 1333, when tofu began to appear in regular homes, and by 1338, tofu was recognized as a daily food eaten by all members of the society. Tofu was very popular because it was a rich protein source that was relatively inexpensive.

The Japanese invented dried-frozen tofu, deep-fried tofu burgers and pouches, grilled tofu and silken tofu, all which were non-existent in China. As tofu increased in popularity, famous tofu restaurants opened and tofu was developed to become softer, whiter and more flavourful.

World War II brought about new developments to the processing of tofu. One example is the replacement of the curding agent, Nigari, with calcium sulphate. Calcium sulphate was easier to use and yielded a higher amount of tofu which lead to increased profits. It also increased the calcium content of tofu which was desirable.

During the 1960s, tofu factories were developed and pasteurization of tofu was introduced. This method allowed tofu to have a longer shelf life.

East Asia

Tofu did not originate but was transmitted from Southern China to countries such as Malaysia, Indonesia, Vietnam, Philippines, Taiwan and Thailand in the 1900s.

Western Countries

Many references were made about tofu by different people in western countries; however, no records of tofu inventions were discovered. Many large tofu plants owned by Asians were built during the late 1900s in large cities found in Europe and the United States.

Tofu Processing

Coagulants

If you look at the ingredients list on any packaged tofu, you will see either one or more of these terms: calcium sulphate, magnesium chloride, or glucono-delta-lactone. These are coagulants which are necessary in tofu production and are also legal additives in Canada.

Tofu coagulants serve many functions, including their various contributions to flavour, texture and of course curd development. Additionally, each of the coagulants differ in their simplicity and usage. The difference in bulk yields also explains why some coagulants are favoured over others.

Traditionally, the most commonly used coagulant for tofu was known as nigari. Refined nigari is made of 99.5% magnesium chloride and is a powder that can be isolated from sea water. It is still widely used in Japanese tofu industries because it produces the most delicious flavor in tofu. Generally, nigari is used to produce firm tofu because it incorporates little water during curd formation. Nigari is also difficult to handle due to its rapid reaction with soymilk, causing the decrease in water absorption. Additionally, because it produces much lower yields, and causes the tofu to have a coarse texture , many countries have switched to using calcium sulphate during World War II.

Nowadays, the most popular coagulant is calcium sulphate which produces a mild flavour with a plain taste. It helps to assemble curds by forming small water bubbles inside the tofu. Calcium sulphate is easy to use as it is a non-hygroscopic powder (does not absorb water). Having low solubility, it allows the protein of the tofu to coagulate at a slower rate resulting in smoother curds, higher water absorption and softer texture. Compared to the traditional coagulant, nigari, calcium sulphate also helps to yield more tofu contributing to a potential increase in profits.

It is thought that neither calcium sulphate nor nigari (magnesium chloride) extends the storage life of tofu.

However,glucono-delta-lactone, an example of a relatively newly discovered food additive can yield higher production as well as increase storage stability. It is made through the fermentation of corn starch and differs from calcium sulphate and nigari because it carries out the coagulation process as an acid instead of a salt. It is mainly used to make soft, silken tofu, though it can be combined with calcium sulphate or other coagulants to make firmer tofu.

Additives have often been a concern of consumers; however, the amount of additives that are being consumed along with tofu is actually quite little. When reacting with proteins, the coagulants break down into ions. Most parts, which are not reactive, will dissolve in the liquid and be eliminated before the tofu is ingested.

Traditional vs. Commercial Methods

Tofu-making originated in China, then spread to Japan. It is in Japan where much of the making process became modernized and standardized.The commercial method of processing is similar to the traditional process, however, it is much more automated. With the use of high technology equipment, a more efficient way of tofu production can be carried out with faster production and decreased contamination. The following chart outlines a commercial method of tofu production developed by the Superior Tofu company. (Please note that the use of this information is for educational purposes only.)

	Commercial Method	Traditional Method
Coagulants	Calcium sulphate, magnesium chloride, glucono-delta-lactone (nigari is still used in countries such as Japan)	Nigari (sea salt)
Ingredients	soybean milk, water, coagulating agents	soybean milk, water, coagulating agents
Processing Procedure	1) Soak the soybeans in water 2) Pump soybeans through various high speed grinders and extract the juice with multi-stage centrifugal filters and ultra-fine sieve shakers 3) Juice is pumped into a boiler that is temperature and pressure controlled 4) Remove contaminants via sophisticated filter systems 5) Use high power ultraviolet sanitizers to kill germs in the water 6) Add coagulant to form curds 7) Blend the soy pudding in several stages 8) Pour the blended soy pudding into a forming box to drain 9) Press the tofu to release excess moisture 10) Cut and package tofu	1) Soak the soybeans in water for 12-14 hours. 2) Mash and mix soybeans with water and boil it. 3) Squeeze out the soy milk. 4) Add the coagulant to form curds. 5) Press the curds. 6) Cut and package tofu
Additional Preservation	Apply thermal processing by sending boxes into a hot bath and then place in cold water for a few minutes. Products are stored in cooling facilities before delivery to retail stores and restaurants.	Pasteurized at 82˚C which extends shelf life for about 30 days. The tofu must be stored below 7˚C after that.

Preservation Methods

With the long history that tofu has, many different ways of tofu preservation have been introduced and are currently implemented around the world. The methods that people are most aware of involve exposure to low temperatures or high temperatures which can often create new textures in the tofu. Fermentation is also a unique way of preserving tofu. This section provides a brief overview of the common ways to preserve tofu as well as methods that are currently under investigation.

Low Temperature Preservation Methods

Dried-Frozen Tofu

Dried Frozen Tofu[2]

This type of preserved tofu originated in Japan. This preservation method allowed lightweight tofu to be produced, which could be stored well. One of the origins of dried frozen tofu is Mt. Koya in Japan. The system developed there was to have firm tofu frozen outdoors and then allowing it to remain in a shed for 5-15 days exposed to below freezing temperatures. The tofu was then thawed with warm water and pressed lightly to remove melted ice. Lastly, the tofu was heated using charcoal braziers which allowed it to dry.

Another technique which was more accessible was developed on the mountains of Nagano, Japan. First, firm tofu was frozen in the snow and wrapped in straw mats to store in a cold barn for 1-7 days. After 7 days, the tofu was tied with rice straws and hung from poles under farmhouses where there was no sunlight. The tofu was allowed to dry for a few weeks.

The basis behind making frozen tofu is to apply cold temperatures and drying methods to increase its shelf life. Once the tofu is coagulated, cut, and pressed, developing a firmness equivalent to that between silken tofu and firm tofu, it is allowed to freeze at a temperature of approximately -10°C. Tofu is stored in the freezer until it is completely solid. Note that after freezing, the colour of the tofu will become yellow. The frozen tofu will be stored at -3°C for 20 days and then thawed by spraying warm water. The thawed tofu will be pressed to remove excess water before the final drying step. The drying takes place in a series of four rooms with controlled humidity and decreasing temperature from 100°C to 40°C. Hot air is blown onto the tofu until it is dried. This process takes about 2 hours to complete.

Baking powder containing potassium carbonate and other various salts are used to soak the tofu before the drying process. This makes the dried tofu softer, less bristle and also changes the yellow colour of frozen tofu to pristine white. Tofu dried in this method has a very porous structure, making them effective in absorbing seasoning flavours. Before cooking, this type of tofu must be reconstituted by soaking the tofu in plain water.

Dried-frozen tofu can be stored in normal room temperature for up to 8 months and up to 1 year if refrigerated.It must be stored away from sunlight and moisture because it can slowly turn brown if not stored correctly.

At home, tofu can be preserved by first draining the tofu, then freezing the tofu and thawing it before consumption. This type of preservation method for freezing tofu is not available commercially.

Freeze Drying Tofu in miso soup package required water to rehydrate[3]

Freeze Drying

Freeze Drying Tofu in miso soup [4]

Not to be confused with dried frozen tofu from above (although some websites do use the term "freeze-dried" to describe Dried Frozen tofu), freeze drying is a new technology that involves a completely different process. Specialized equipment must be used, thereby making it a rather expensive procedure, but it allows food to be stored at an ambient temperature.

Freeze-Drying involves changing solid ice directly to gas. The food product first needs to be frozen. The method and temperature used is very critical to the success of the freeze drying procedure. As water freezes to form ice crystals, the freezing temperature of pockets of solute lowers and becomes more and more concentrated. So the initial freezing of the food needs to take place at a temperature where everything including the solute in the food is properly frozen. If this is not achieved, those pockets of solute could expand and damage the structure of food during the freeze-drying process. Once the food is properly frozen, drying can take place. During this process the temperature is raised and the pressure is lowered just enough for the solid ice to sublime. A moisture trap will be used to collect the leaving water vapour to ensure the drying of the food.

The tofu seen in AMANO Miso Soup Mix is an example of freeze-dried tofu During freeze drying, tofu is placed in a chamber at a temperature around -30°C. The chamber is then pressurized to 0.3 atm and the ice is heated by raising the temperature. The ice will soon begin to sublime leaving the tofu behind. There will be no change in the texture, taste or flavour of freeze-dried tofu, and it will appear to be a freshly made piece of tofu once water is added. AMANO’s miso soup mix has a shelf life of 1 year.

High Temperature Preservation Methods

Aseptic Packaging

Aseptic packaging is a method used to sterilize packaged foods with the goal of killing microorganisms inside the food.The process involves packaging sterilized products into sterilized containers. The packaging material is also sterilized in order to prevent recontamination. Methods of sterilization can include using high temperatures, radiation, and chemical substances such as hydrogen peroxide.

In order to increase the shelf life of tofu, aseptic packaging is an effective method. Before packaging the tofu, the soy bean milk used to make the tofu is first sterilized using Ultra High Temperature treatment . The aseptic packaging system will then add the coagulating agent and package the tofu.

One example of aseptically packaged tofu is MORINAGA silken tofu. They used the Tetra Brik packaging developed by TETRA PAK of Sweden The soy milk used in its tofu production is treated with ultra high temperature of around 140°C briefly for sterilization and the tofu container is sterilized by going through a 30% hydrogen peroxide bath at 70°C for 6 seconds. The sterile environment is then achieved through hot air and steam. After the coagulant is added to the soy milk, the package is sealed and then heated to around 90°C to help the tofu solidify. Unopened MORINAGA tofu has a shelf life of 1 year under a cool dry environment.

Deep-Fried

Fry the cubes of tofu till turning to golden-brown colour by submerging them with oil. by Foodlover

Tofu can be deep fried, which involves heating it in oil at a high temperature. The hot oil causes water in the the tofu to evaporate. This phenomenon leads to the drying of the tofu, replacing the water content with oil. The decrease in water activity and increase in oil content will enable the extension of the storage life of tofu, since microorganisms require free water in order to carry out chemical and biological reactions, helping them survive and multiply. With the deep-frying of tofu, the texture of the tofu could range from porous to crispy depending on the type of tofu used and the preparation method. With proper packaging and refrigeration, deep fried tofu could be stored up to about one month.

Although lowering the water content will minimize the risk of bad microorganisms in food, our group agreed that the high fat content of deep fried tofu could also be harmful to one's health by increasing the risk of cardiovascular disease upon consumption.

Pasteurization

Pasteurization is a process that uses a specific temperature for a specific length of time to kill disease-causing microorganisms. It is a process invented by French scientist, Louis Pasteur.

Pasteurization of tofu takes place after the tofu has been packaged to increase shelf life. The pasteurization temperature applied varies with different manufacturers. The Mastuda-Hinode tofu factory pasteurizes the packaged tofu at 85°C for 50 minutes and then cools it at 1-2°C for another 50 minutes. Tofu that goes through this pasteurization process can last at least 3 weeks. Pasteurized tofu must be kept refrigerated.

Fermentation

Spicy Stinky Tofu [5]

There are two basic types of fermentation tofu products, the Traditional Chinese Style and the Western style which is known as Tofu Cheese. We focus mainly on the Chinese fermentation style.

The Traditional Chinese Style has many different fermenting methods where each may result in a tofu with different colour, texture and taste. One type of tofu has a stinking smell, and is known "Chou Dofu" or Stinky Tofu. This kind of tofu is made by fermenting fresh tofu in rice wine. It is a fast fermentation process lasting around 12 hours. Spiny amaranth, bamboo shoot and wax gourd, decomposed by natural fermentation for over 6 months, are the main components of the fermented brine. The tofu is then immersed in the stinky brine to carry over the stinky odor. The additions of Chinese medicinal herbs, such as orange peels, result in different flavours in different kinds of stinky tofu. Sometimes this tofu is green in colour due to the addition of Mucor mold. This kind of stinky tofu is very popular in Hunan, Jiangsu, and Zhejiang provinces as street snacks.

Pickled Tofu[6]

Wang Zhihe Fermented Bean Curd is an example of this kind of tofu that is available in glass jars sold at market places. This brand has a history of over 300 years. Wang Zhihe's special fermentation recipe produces a special fragrance among the strong smell that makes it popular in the market.

The most popular type of fermented tofu in China is pickled tofu which is usually used as food seasoning or served as part of a Chinese breakfast. It is also called Wine-Fermented Tofu or "Furu", and is usually made in white or red colour. The production process starts by using firm tofu that has been cut up into 1 inch cubes. Mold spores such as Actinomucor elegans, Mucor racemosus, or Rhizopus speciess, are inoculated into the tofu cubes and then incubated for 3 days at 20°C.

If individuals want to make their own pickled tofu at home, the tofu may be fermented by itself when left in open air. It will take approximately 2-10 days for the moldy coating to appear on the surface. The freshly molded tofu can be stored in sealed bottles together with rice wine, salt and other spices for around 2-6 months.

Hwang Ryh Shiang Co., LMT, produces this type of fermented tofu and is available in three flavours: chili, orginal, or red date.

Preservatives

Curcumin is protected by Microcapsule to improve curcumin solubility and stability.[7]

Curcumin Microcapsules

Curcumin is a pigment which can act as both a natural colorant and a preservative for food due to its antimicrobial effects. Curcumin(Kurkumina) is the extract from the popular Indian spice turmeric which is a member of the ginger family. It is especially affective against Bacillus subtilis, Escherichia coli and Staphylococcus aureus. When preserving tofu, curcumin is added after heat treatment of the tofu, and studies have shown that mold growth was eliminated. This preservative is currently being investigated in China and it is not used in tofu preservation in Canada. We suggest that scientists should complete more testing on the safety of this additive. Approval of this preservative may spark a new and useful preservation tool for tofu and other processed foods in the near future.

Ocimum Sanctum

Ocimum Sanctum, a.k.a. Holy Basil[8]

Ocimum sanctum is a natural preservative in tofu, contributing to the storage of tofu. It is also known as the Indian Holy basil or sacred tulsi. After treating with tulsi, the pH of tofu will decrease to a value lower than that of regular tofu within the first 24 hours of storage. Generally, after a week of storage, tofu protein will loosen and water absorption will increase to about 5%; however, tulsi-treated tofu minimizes this water absorption to 1%, thereby proving that the structure of the tofu is still intact. Experiments have determined that the flavor, aroma, appearance and quality of the tofu is not affected. The application of the preservative also allows the tofu to be stored without refrigeration for more than 7 days. This preservative is currently being tested in India and widely used as one of Indian traditional tofu preservation methods; however, it is not used for tofu preservation in Canada, yet. More experimentation should be completed to ensure the safety of the substance.

Video of Tofu preservation

In this video, we demonstrated how to preserve tofu in three different ways. First, you will see how fermented-pickle tofu and deep-fried tofu methods are used; then, you will see commercially and home-made frozen tofu. Finally, we will show you a freeze drying version of tofu.

Benefits of Tofu Consumption

Nutrition

Made from soybeans, tofu provides a great source of protein that is low in fat. Unlike most plant-based proteins, soy is a complete protein . This means that it contains all the essential amino acids necessary for optimal body functioning for humans. As a result, Best Health Magazine suggests that soy products such, as tofu, are suitable vegan substitutes for meat products in the diet. .

In addition to being a great low-fat protein source, packaged tofu commonly contains several nutrients. The Dietitians of Canada states that tofu consists of major minerals:

Calcium: essential for building and developing strong bones and teeth
Zinc: necessary for growth, immunity, wound healing and perceiving taste
Iron: used to carry oxygen to tissue and muscle cells

Other important minerals in tofu include magnesium, selenium, potassium, and phosphorus. .

Health Claims associated with Soy Products

In 1999, after the evaluation of 27 studies, the U.S. Food and Drug Administration (FDA) approved the health claim that a diet low in cholesterol that includes 25g of soy protein per day may reduce the risk of heart diseases . A certain soy food product qualifies for a label containing this soy health claim must contain at least 6.25 g of soy protein, less than 3 g of fat (less than 1 g saturated), less than 20 mg of cholesterol, and less than 480 mg of sodium per serving. As a dietary intervention to lower cholesterol, the National Cholesterol Education Program suggests substituting high-fat animal proteins with soy proteins A study involving 42 healthy adult males was conducted to investigate the difference between diets containing 150g of lean meat per day was compared to a diet substituted with 290g of tofu. Over the course of a month, it was found that the tofu intervention lead to a significant decrease in HDL levels while lowering LDL levels.

Although there is a health claim regarding the consumption of soy products in the U.S., no such health claim is approved in Canada. As Health Canada has not accepted health claims involving soy products, this must mean that more studies must be conducted by Canada in efforts to investigate whether soy intake improves cardiovascular outcomes as well as other concerns. We believe that it is necessary for Canada to stay strict about their approval of health claims with evidence from effective research and experiments.

Another benefit of tofu would be Phytoestrogens that are found in soy--especially isoflavones. According to WHFods, the isoflavones, genistein, and diadzein (found in tofu) are able to attach to estrogen receptors and act as weak imitations of estrogen. These substances are able to provide enough estrogen activity to reduce the uncomfortable symptoms resulting from a sudden drop in estrogen levels during menopause. Moreover, controlled studies regarding isoflavones in soy products have also suggested that the substances contribute to a lowered risk of breast cancer and bone loss in premenopausal women.

Disadvantages of Tofu Consumption

Health Risks

The Centers for Disease Control and Prevention reports cases of foodbourne botulism resulting from preparation of fermented tofu at home. Foodbourne botulism results from consuming foods containing Clostridium botulinum spores. . Although C. botulinum spores normally exist in the environment, the practice of correct food-preparation steps inhibit spore germination and toxin production. The rare growth of C. botulinum and production of toxin in the tofu was suggested to have been facilitated by the almost neutral pH of the fermented tofu, boiling the tofu, potentially (creating an anaerobic environment) and storage at room temperature for days after preparation

The Cancer Science Journal reported that eating excess amounts of fermented tofu can lead to gastric cancer as compared to eating non-fermented soy products The high risk is associated with high levels of nitrate or nitrite, large amounts of salt, and loss of key nutrients under acidic and, oxygenic conditions as a result of fermentation processes

Our group realized that the presence of nitrites in foods is a controversial topic. As we discussed in FNH 200 lecture, the presence of nitrites and nitrates in food leads to the formation of nitrosamines which is a potential carcinogen. However, it is known that nitrites inhibit growth and thus toxin production by C. botulinum. As fermenting tofu is associated with a risk of foodbourne botulism, it is also beneficial. Although nitrites naturally occur in fresh food, exposure to nitrites from fermented tofu on occasion is not an extreme concern. However, it is definitely the most beneficial to minimize nitrite intake whenever possible to reduce harmful effects.

Allergen

Health Canada notes that soy is one of the top ten priority food allergens. Individuals who are allergic to soy should avoid all food and products containing soy or soy derivatives with soy protein such as tofu (which are made of soy beans). If soy is part of the product formulation, Health Canada states that it must be declared in the list of ingredients or in a separate "contains:" statement immediately following the list of ingredients.

Undesirable Flavours

Another disadvantage, although not a health risk, is the chance of undesirable flavors produced during the process of making tofu. During the production of tofu, there are often undesirable, or “off-flavors” produced through enzymatic lipid oxidation and autoxidation during the processing of soybeans. More specifically, the off-flavors are produced when soaking the raw soybeans for long periods of time and at high temperatures before the grinding process. One method of reducing these undesirable flavors from occurring is soaking the beans at a lower temperature, usually 2-4̊ C.

Because there are microorganisms present during the soaking and grinding processes of soybeans, heat can help reduce the microbial content. However, this heat will not destroy all microorganisms at this stage. During the grinding process, the temperature used during grinding is very important and could result in mushy or produce undesirable flavors. For example, high temperature water will produce a bland flavor of soy milk during the process. Not only is there a risk of off-flavors during the process of tofu, the temperature of the water during the grinding process can have negative effects on the overall texture of the finished product. If the temperature of the water is increased, between 0 and 50̊ C, then the firmness of the tofu decreases.

Shelf Life

Many tofu products are packaged in trays of water and because these products are usually pasteurized, the shelf life will only last 3 to 4 weeks if kept properly refrigerated. However, if the tofu is “fresh,” it is unlikely that the product has been pasteurized. Therefore, the shelf life of the fresh tofu will be 1 to 3 days if properly refrigerated. Silken tofu, because it has been sterilized, will have a longer shelf life of up to 6 months.

Genetically Modified Organisms (GMOs)

Because of genetically modified soybeans, there is concern about genetically modified crops. For example, Brazil nut genes were spliced with soybean genes for the purpose of additional protein. However, this poses potential allergy risks for people allergic to nuts. Also, phytoestrogen compounds, which are believed to help protect against disease and cancer, are lower in genetically modified soybeans.

Exam Review Question

One day your mother is making miso soup using a pack of soup mix. You curiously test her to see if she knows how the tofu in the soup package is preserved. She replies that it is preserved in the same way as the dried frozen tofu. Is she right? Explain the preservation method of each type of tofu if they are different.

ANSWER:

Tofu in the miso soup mix is preserved through freeze-drying methods.

Dried-frozen tofu is preserved by freezing and thawing, followed by a drying procedure.

Freeze-dried tofu: The tofu is first frozen at about -30degrees celsius, then placed in a vacuum-sealed chamber/freeze dryer. In order to dehydrate the frozen tofu, heat and pressure is applied from within the freeze dryer to sublimate the ice(ice to water vapour). The water content leaves the tofu as a gas.

The texture and taste of the tofu is unchanged before and after the freeze drying process.

Dried-Frozen Tofu

Once tofu is coagulated, cut and pressed to develop a firmness of that between silken and firm tofu, it is frozen at a temperature of about -10degrees Celsius until completely solid. After, it is to be stored at -3degrees Celsius for 20 days and then thawed using warm water. The tofu is then dried in controlled environments.

Dried-frozen tofu will change colour and develop a more meaty texture after processing.

• Note that although the two methods may seem similar both in their names and their preservation methods, they are actually very different. Freeze-dried tofu does not encounter any water during processing whereas dried-frozen tofu does. The product produced by both methods is also significantly different!

Conclusion

During tofu processing, most coagulants work in similar ways. The traditional Nigari (magnesium chloride) enhances tofu flavour; however, the rapid tofu formation gives lower yields and crude texture. The application of calcium sulphate produces tofu at a slower rate to ensure a smoother and softer texture. Yet, both coagulants do not increase the shelf-life. On the other hand, glucono-delta-lactone can yield higher productions as well as increase storage stability. Though it is mainly used to make soft tofu, it can be combined with other coagulants to produce different textures. Hence, glucono-delta-lactone may be the potential coagulant favoured over others. We believe that the use of this additive will become more widespread in the future.

While some preservation methods change the colour, texture, odor, and flavour of tofu, such as deep frying and fermentation, these methods also add more characteristics to the tofu product which may be appealing to certain consumers. However, we think that the best way to preserve tofu is by freeze-drying. This allows the tofu to be stored for a long period of time in a dried form, and since its texture is not destroyed through the process, it will turn out to be the same as regular tofu when rehydrated. This allows for flexibility for the tofu to be used for different purposes, whereas fermentation and deep frying may limit the variation in consumption methods. We believe that freeze-drying should be more widely used to preserve tofu of larger sizes, which implies that a more effective and cheap method must be incorporated. Some preservation methods can be completed at home as listed in the video; however, much attention needs to be given towards avoiding contamination and using proper handling to ensure that the tofu is safe for consumption.

Most people think tofu is a good resource for protein, based on its nutrition facts and the health claims related to soy products; yet, there are still some disadvantages because of issues related to health risks, allergen, undesirable flavours, shelf life, and GMOs on tofu. We encourage increased research to be applied to tofu in order to make it a more appreciable product for consumers.

Through this project, we were able to explore the unique ways of preserving tofu, broadening our exposure to historical and newly discovered knowledge. We hope that readers will have felt the same way after reading through this wiki page.