Ferment III (Shoyu)
September 20, 2010
Shoyu is a fermented soybean product known to the English speaking world as soy sauce. Although, much of what is sold as soy sauce is not produced by fermentation at all but is the product of a chemical process using soy extract, ethyl alcohol, sugar, salt, food colouring and preservatives. Tamari, originally a byproduct of the miso making process is now brewed, using a similar process to traditional shoyu making but without the addition of wheat.
Soybeans are soaked, cooked (boiled or steamed) and left to cool. Cooling is facilitated by dividing cooked beans amongst a number of containers and regularly turning the beans to bring the hot ones below to the surface and fanning those on top. The amounts placed in each container are precisely measured to ensure the correct relative amounts of wheat can be added later.
Wheat is dry roasted. A slow even roasting is achieved by constant stirring over low heat. This can be done in batches and as long as the colour of each batch is similar an even roasting across batches has been achieved.
Roasted wheat, now cooled to room temperature, is mixed with koji (Aspergillus oryzae) and divided into equal amounts relative to the number of batches of soy beans cooling in the containers.
Wheat, koji and soybean mix is spread out onto bamboo trays covered with cotton inside a ‘plastic house’ (the greenhouses typically used by Japanese farmers). The next stage of the process, where the koji mycelium spreads through the bean and grain mix, requires a warm and humid environment, hence, the plastic house.
In two to three days the koji will colonize the bean/grain mix and cover it with a fluffy, fragrant mold mycelium.
The bean/grain/mycelium mix is poured into a brine (sea salt and good quality water) and thoroughly mixed. From this point on the mixture (moromi) will need to be stirred every day for about one year after which it will be stirred every other day for another year. When stirring it is important to keep the sides of the barrel clean as it is here that contamination is likely to occur. The inside of the barrel above the level of the moromi should be carefully wiped down after each stirring.
Following is a description of what is occurring during the aging process. It comes from the wonderful book Culinary Treasures of Japan: The Art of Making and Using Traditional Japanese Foods by Jan & John Belleme, 1992 (New York: Avery Publishing Group).
[E]nzymes from the koji and the naturally occurring yeasts and bacteria slowly breakdown the complex carbohydrates, proteins, and oils of the wheat and soybeans into sweet sugars, aromatic alcohol, and flavorful amino and fatty acids.
After about two years the moromi is placed in cotton sacks and pressed. The soy oil that rises to the top is skimmed off and you have the shoyu. It is left to settle, pasteurized under low temperature and bottled.