Soy sauce is made by inoculating equal parts of cooked soybeans and roasted cracked wheat with a culture of either Aspergillus oryzae or A. sojae. The mixture, called koji, is allowed to stand for several days, during which time carbohydrates and proteins in the soybeans are broken down, producing a yellow-green liquid containing fermentable sugars, peptides, and amino acids. After this initial step, the mixture is put into a large container with an 18% NaCl solution, or brine. Salt-tolerant microorganisms then grow and impart changes over an extended period. Microorganisms involved in this stage of fermentation include lactobacilli and pediococci, as well as the yeasts Zygo-saccharomyces rouxii and a species of Torulopsis. The brine mixture is allowed to ferment for 8 to 12 months, after which the liquid soy sauce is removed. The residual solids are used as animal feed.
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