TOFU, TEMPEH, SOYSAUCE AND MISO
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The differences in consumption patterns for soy protein foods between the West and the Orient were outlined by D. Fukushima of Kikkoman Foods, Inc. (U.S.A.), who wrote: " There are significant differences in the use of soy proteins for human consumption in the U.S. and in the Orient. In the U.S., the soy proteins are used as ingredients of a wide variety of foods, e.g. hamburgers, sausages, meat loaves, dairy products, breads, pastries and cookies. In the Orient, however, soy proteins have been consumed for thousands of years, not as an ingredient, but as characteristic, unique soy protein foods." (Fukushima, 1981).
A detailed discussion of the multitude of traditional soy foods of the Orient is beyond the scope of the present work. Only four traditional products and their production technology will be described. These four products were selected, not only because of their leading position in the Orient, in terms of consumption levels, but also in view of the growing interest that they have recently created among Western consumers and food manufacturers.
Traditional soy protein foods are usually divided into two groups: fermented and non fermented. Miso, soysauce and tempeh are representatives of the first group. Tofu, together with soymilk discussed in the previous chapter, belong to the second. Nevertheless, fermented varieties of tofu and soymilk also exist.
It should be stressed that each one of the four foods is, in fact, a group in itself, comprising many distinct variations.
Historically, most traditional soy protein foods originated in China and were introduced later to other countries in East and Southeast Asia. At present, however, Japan occupies the leading position in this field, with respect to industrialization, technology development, equipment manufacture and worldwide marketing.
9.2 Soy sauce
Soy sauce is a dark brown salty liquid with a peculiar aroma and a meaty taste. It is the chief savory seasoning agent in Oriental cookery, but it is becoming increasingly popular in many other regions of the world. Once a home-made staple, it has become an important industrial product. Industrialization has altered the production process, changed the raw materials used, standardized the products and modified somewhat their characteristics.
The main ingredients of soy sauce are soybeans (or defatted soybean meal), wheat, salt and water. The heart of the manufacturing process is a complex fermentation whereby the carbohydrates are fermented to alcohol and lactic acid and the proteins are broken down to peptides and amino acids. Chemical reactions between the original components and the fermentation products create the colour , consistency and aroma of soy sauce. Formulations and processing conditions differ from one country to another and in function of the type of soy sauce to be produced.
The process of manufacturing soy sauce can be divided into three stages: preparation of the "koji", fermentation in brine and product refining.
Fig.42 describes the basic outline of the manufacturing process of "koikuchi" sauce, a representative type of Japanese soysauce. Soybeans and/or defatted soybean meal are cooked in continuous pressure-cookers and mixed with roasted and coarsely broken wheat. The mass is inoculated with a mould- Aspergillus orizae (or A. sojae) and incubated in shallow vats with perforated bottoms and air is forced through the mass. After three days of incubation under controlled conditions of temperature and moisture, mould growth covers the entire mass which turns greenish as a result of sporulation. This mass is called "koji". Koji is the essential ingredient of most fermented products of the Orient. It is a concentrated source of amylolytic and proteolytic enzymes necessary for the decomposition of the carbohydrates and proteins.
Figure 42: Production of "koikuchi" Soysauce Source: Fukushima (1981)
In the refining stage, the fermented mash is pressed to separate the sauce from the solid residue. the sauce is filtered, clarified and heated to 70-80o C. Heating is necessary to pasteurize the sauce and to develop the characteristic colour and aroma. After final clarification the sauce is bottled.
The use of defatted soybean meal instead of whole soybeans is justified, since most of the oil is lost in the residue.
Tamari soy sauce is popular in Southeast Asia. It contains a much lower proportion of wheat and therefore less alcohol in the final product.
In modern soy sauce plants, all the steps of the process , including the making of koji, are mechanized and the process conditions are fully controlled. Material losses are minimized through recovery operations. Thus, 90% of the raw material nitrogen is recovered in the product.
Soy sauce typically contains 28% soluble solids (18% salt and 7% protein).
Miso is a fermented soybean paste. It serves as an all-purpose seasoning, a concentrated "instant soup" and a good source of protein. The main ingredients used for its preparation are: soybeans, rice (or barley), salt and water.
As in the case of soy sauce, the production of miso is a three-step process: preparation of the koji, fermentation in the presence of salt at high concentration and finishing.(Fig. 43)
Figure 43: Flow diagram for Miso production Source: Fukushima (1981)
Koji for miso is prepared from cereal grains (most commonly, rice) alone. When the mould has grown sufficiently on rice, salt is added to arrest further growth. The salted koji is mixed with cooked, mashed whole soybeans and water is added to reduce the solids content to about 50-52%. The mass is inoculated with salt tolerant lactic acid bacteria and yeast cultures and allowed to ferment at 30o C for two weeks to 6 months in closed tanks, under pressure.During this period, the semi-solid mash is transferred from one fermentation vessel to another for the purpose and mixing and accelerating the fermentation. When the paste is sufficiently ripe (depending on the type of miso) , it is blended, pasteurized and packaged. Benzoate and/or sorbate are sometimes added as preservatives.
Several varieties of miso are produced, differing in formulation, salt concentration and ripening time. "Mild" miso is light coloured while the ripe varieties are brownish-red.
Fat is an essential component of miso. Therefore, whole soybeans and not defatted meal are used as the starting material. A "hot" variety, flavoured with generous amounts of red hot pepper, is produced in Korea.
Dehydrated and freeze-dried miso are produced in Japan and the U.S.A. as ingredients for instant dry soups, or as seasonings.
Typically, miso contains 50-60% solids, 10-14% protein, 3-6% oil, 8-14% salt, 3% fibre. A special type of miso, made from soybeans and salt only, is produced in smaller quantities. It has a dark colour and higher protein content, over 19%.
Tempeh is a fermented soybean product of Indonesian origin. It consists of cooked, dehulled whole soybeans which have been fermented by Rhizopus moulds. It is a moist solid cake with a mild, pleasant taste . It is usually sliced, dipped into a salt solution and deep-fried in oil. The traditional product is highly perishable and is usually consumed the day it is made. In industrial production, it can be preserved by drying or freezing (after blanching to inactivate the mould and its enzymes.)
Production methods vary as with most traditional foods. In a typical process, soybeans are soaked in water, dehulled and then cooked in boiling water for one hour. After draining the soybeans are spread out for air-drying of the superficial moisture. Tempeh from the previous day is used as a starter. The prepared soybeans are thoroughly mixed with the starter, wrapped in banana leaves and left to ferment for one to two days. Mould growth is vigorous and the whole mass is soon covered and bound together by Rhizopus mycelium.
Typically, tempeh contains 35% dry matter, half of which is protein. Unlike the previously discussed fermented soy products, tempeh does not contain salt.
Tempeh is still, predominantly a home-made or cottage-industry product in Indonesia and Malaysia. It is practically unknown in Japan. However , it has been introduced to the U.S.A. and to Europe, mainly for the population of Indonesian origin and for the rapidly expanding Indonesian restaurant trade. It is made in modern, sanitary plants, using stainless steel equipment and sometimes, pure cultures of mould.
The traditional banana leave is replaced by suitable plastic materials or foil, perforated to provide the moderate aeration necessary for mould growth without excessive sporulation. Commercial dehulled full-fat grits can be used instead of whole soybeans.
A diagram describing a modern variation of the tempeh production process, developed at the Northern Regional Research Centre, in Peoria, Illinois, is shown in Fig. 44.
Figure 44: Flow diagram for Tempeh production Source: Wang (1984)
Tofu is the representative of the "bean curd" foods, the most popular type of traditional soy protein products. Bean curd (Fu Fu or Tu Fu) has been prepared and consumed in China for thousands of years and a written record of its preparation dates from the second century B.C. Bean curd is a product by itself or a starting material for a variety of related products, including fermented, salted, smoked, dried and fried derivatives. Tofu is the Japanese name for bean curd products.
Tofu has been made in the U.S.A since the beginning of the century, as an ethnic food. Its consumption in the West increased rapidly since the 1970s , mainly as a vegetarian alternative to meat and cheese or as a novel food by itself. The development of a highly successful tofu-based all-vegetable ice-cream was a significant factor in the recent growth of tofu production in the West. Today, a variety of types and brands are available in most supermarkets.
9-5-2 Regular and silken tofu
Basic regular tofu is a white, essentially bland, soft product, closely resembling pressed white milk curd. Its production starts with the preparation of soymilk, as described in the previous chapter. Soybean is boiled, then cooled to around 75o C. The thin protein-lipid film (surface scum) formed on the surface of the milk is removed. A coagulant, which consists of a slurry of gypsum powder or a solution of magnesium salts (nigari) is added. Curdling occurs. The free supernatant whey is removed and the curd is transferred to perforated boxes and pressed until a coherent block of curd is obtained. The curd is next immersed in cold running water for several hours, with the purpose of cooling and leaching out excess coagulant and entrapped whey solids. The block is cut to retail-size portions and wrapped for marketing. Fresh tofu is stored, transported and sold as a refrigerated perishable. The analogy between tofu production and cheese manufacture is evident.
A radically different method is used for the industrial production of "silken tofu", a softer and more fragile type of bean curd. Here the production process resembles yogurt rather than cheese manufacture. Soymilk wit a high content of solids (10% instead of 5-6% in regular tofu) is heated to 100o C., then cooled to room temperature. Glucono-delta-lactone (GDL) is added and the milk if filled into the retail containers. After sealing, the filled containers are heated in a water bath at 80-90o C for 40 to 60 minutes. At this temperature, GDL is transformed to gluconic acid, which causes the protein to coagulate as a homogeneous gel, with no whey separation.
Silken tofu prepared in this way is a pasteurized product which keeps well for a few days under refrigeration.
A diagram describing the manufacturing process of regular and silken tofu is shown in Fig.45.
A more advanced variation of the process described above is used for the production of long shelf-life silken tofu, using UHT technology. Soymilk with 10% solids content is heated to 130o C and cooled to room temperature in continuous aseptic fashion. The GDL solution is cold-sterilized by Millipore filtration and injected into the stream of the sterilized, cooled soymilk. The mixture is aseptically filled into plastic containers. The sealed containers are subjected to heating, as described below. Aseptically filled tofu keeps well for several months without refrigeration.
The production of regular tofu has also been modernized and adapted to large scale manufacture. The first part of a tofu factory is, actually, a soymilk plant, as described in the previous chapter. The second half comprises the coagulation, curd washing and finishing operations.
The equipment of a complete tofu plant is described in Figures 46, 47
and 48. Fig. 46 refers to the soymilk preparation.
Fig. 47 shows the regular fresh tofu production line. Fig. 48 describes a line for the manufacture of pasteurized silk tofu.
Fig. 49 is a suggested layout for the same tofu plant.
Figure 46: Equipment Flow-diagram of a Tofu Plant
Figure 47: Equipment Flow-diagram
of a Tofu Plant
Figure 48: Equipment Flow-diagram of a Tofu Plant
Figure 49: Layout of a Tofu Plant Courtesy of Nagasawa Co.
In addition to complete automated plants with high capacities, good quality small-scale equipment is available for production at the local shop level.
Being composed of a step of extraction followed by a step of precipitation, the manufacture of tofu is, in fact, similar to that of isolated soybean protein. Just as in the case of ISP, a residue (okara) and a whey are produced. This may be an inconvenience to small tofu plants which do not have the economy of scale necessary to turn the okara into a saleable product, and to dispose properly of the whey. In this case, the use of micromilled soy flour (see Chapter 8), soy protein concentrates and isolates may be preferable to whole soybeans as starting materials.
Kori-tofu is a dry, shelf-stable variety of tofu. The drying technique involves a unique freeze-thaw cycle, to liberate the bound water.
First a tofu is made, using as a coagulant,calcium chloride instead of gypsum. This tofu is cut to square tablets, frozen and kept frozen for up to 3 weeks and then thawed. After the freeze-thaw cycle, a considerable proportion of the water can be pressed out, and the remaining moisture can be easily removed by air drying. The dry blocks of kori-tofu are then cured with ammonia gas and packaged.
Kori-tofu must be reconstituted in water before it is used. Reconstitution is easy, due to the sponge-like structure of the solid created by the freeze-thaw cycle, and the partial solubilization of the protein by the contact with ammonia gas.
In the traditional way of making kori-tofu, the cold nights were used to freeze the fresh curd tablets.
9-5-4 Deep-Fried Tofu
A significant proportion of the tofu production in Japan is further processed to a large variety of deep-fried products, such as "aburage". Deep frying changes the characteristics of tofu and renders it elastic and chewy. Two step frying methods (first step at 120o C, second step at about 200o C) cause considerable puffing of the tofu. The change in texture is so marked that some varieties of deep-fried tofu may be regarded as meat analogs.
9-5-5 Fermented Tofu
Fermented varieties of bean curd are made in China and called Su Fu . To prepare Su Fu, a tough textured tofu with a moisture content of less than 70% is made first. The curd is cut to small (3 cm.) cubes,heated, cooled and inoculated with mould (usually Mucor sp.). After the surface is covered with mycelium (about a week), the pieces are cured for several months in brine containing soy sauce, soy paste, spices and rice wine.
Su Fu is usually packaged in earthenware jars, in a mixture of brine, rice wine and condiments.
Su Fu is a white, creamy food resembling a semi-soft cheese.REFERENCES
Bean Machines Install Three New Systems in North America Soya International 4, No.3, 4.
Escueta, E.E., M.C. Bourne and L.F. Hood (1986)
Effect of Boiling Treatment of Soymilk on the Composition, Yield, Texture and Sensory Properties of Tofu Can.Inst. Food Sci. Technol. J. 19, 53
Fukushima, D. (1981)
Soy Proteins for Foods Centering around Soy Sauce and Tofu J. Amer Oil Chem. Soc. 58: 346
MIYAKO Inc. (1991)
Commercial Communication Miyako Oriental Foods Inc. Baldwin Park, California
NAGASAWA Co. (1990)
Commercial Communication Nagasawa Kikai Seisakusho Co.,Ltd. Kawaguchi, Japan
Wang, H.L. and C.W. Hesseltine (1982)
Coagulation Conditions in Tofu Processing Process Biochemistry, Jan./Feb. 1982, 7.
Wang, H.L. (1984)
Tofu and Tempeh as Potential Protein Sources in the Western Diet J. Amer. Oil Chem. Soc. 61: 528
Yung-Shung, C. (1981)
Soybean Protein Food in China J. Amer. Oil Chem. Soc. 58: 96A
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