There are various fermented soybean pastes in Asia, including miso in Japan, Chiang in China, Jiang in Korea, Tauco in Indonesia, Taochieo in Thailand and Taosi in the Philippines.
There are four basic steps, two of which are concurrent, namely the preparation of koji and of soybeans.
Koji is made on polished rice and represents a source of enzymes that will hydrolyse soybean components. Waxy components in the outer layers of unpolished rice inhibit the penetration by the Aspergillus mycelium. The rice is washed and soaked overnight at 15°C to a moisture content of 35%. Excess water is removed and the material is steamed for 40-60 min. The rice is then spread on large trays and cooled to 35°C. Seed koji (see the section on soy sauce) is added at 1 g per kg rice.
The trays in koji rooms tend nowadays to be replaced by rotary drum fermenters that facilitate control of temperature, air circulation and relative humidity, as well as avoiding agglomeration of the rice. The temperature is held to 30-35°C over a period of40-50 h. In this time, the rice becomes covered with white mycelium. Harvesting occurs before the occurrence of sporulation and pigment development. The material has a sweet aroma and flavour.
Salt is added as the material is removed from the fermenter so as to prevent further microbial growth.
The whole soybeans employed for miso are large and selected for their ability to absorb water and cook rapidly. They are washed before soaking for 18-22 h. The water is changed regularly especially during summer months in order to prevent bacterial spoilage. The beans swell to almost 2.5 times their volume. After draining, the beans are steamed at 115°C for 20 min when they become compressible.
The beans are mixed with salted koji. Starter cultures may be introduced, including osmophilic yeasts and bacteria. The microflora includes Z. rouxii, Torulopsis, Pediococcus, Halophilus and Streptococcus faecalis.
The mixture, known as 'green miso', is packed into vats and anaerobic fermentation and ageing are allowed to proceed at 25-30°C for various periods depending on the character required. Transfer occurs between vessels at least twice. White miso takes 1 week, salty miso 1-3 months and soybean miso over 1 year. The miso is blended, mashed, pasteurised and packaged.
The characteristics of different miso are listed in Table 14.4.
Amino acids represent a significant source of miso flavour, and they are generated from soybean protein by the action of proteinases (which may be supplemented from exogenous sources). Miso contains 0.6-1.5% acids (lactic, succinic and acetic) as a result of sugar fermentation. Esters produced from the reaction of alcohols with some fatty acids from the soybean lipid are also important flavour contributors.
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