The manufacture of traditional soy sauce or shoyu starts with preparation of the raw materials and addition of the koji (Figure 12-1).The soy fraction consists of either whole beans, soy meals, or soy flakes. It is now common to use de-fatted flakes rather than whole beans or flakes to improve yield and reduce fermentation times. When beans are used, they are washed, sorted, and soaked overnight, then cooked under pressure and cooled rapidly. Flakes are simply soaked and cooked (as for whole beans). At the same time, whole wheat kernels, if included, are roasted and crushed. The wheat adds flavor and color, reduces the moisture so that growth of undesirable bacteria is minimized, enhances mold growth, and contributes glutamic acid-rich proteins. When wheat is used, the soy-wheat ratio depends on the manufacturer's preference and can range from 50:50 to 67:33.
The soy bean-wheat mixture is then inoculated with either tane koji or a pure culture of suitable fungal strains of A. oryzae or A. sojae to start the koji fermentation. As described above, the inoculated material is incubated in large trays, boxes, or vats that are perforated to allow air and moisture to circulate throughout the material and to enhance fungal growth. The temperature is maintained at about 30°C, which means that the incubation rooms or vats must have cooling capacity, since fungal growth generates heat. Once the koji is mature (i.e., covered completely with mold), it is fully developed and ready to be used for the fermentation.
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