The Soy Sauce Professor's Column

The soybeans are steamed at a high temperature and pressure. When heated, the soybean proteins change shape, and become easier for the koji mold's enzymes to act on.

The wheat is roasted at a high temperature, then crushed with rollers and the like. Its starch pregelatinizes, and becomes easier for the koji mold's enzymes to act on.

The salt is dissolved in water to make salt water. It's the source of the salty taste. In addition, it keeps harmful organisms such as putrefactive bacteria in check, and gently allows useful microorganisms, such as lactic acid bacteria and yeast, to work.

The soybeans are mixed with the wheat, and have a fermentation starter (koji mold) added.
The koji mold is cultivated for about three days in a koji production room, which has a temperature of around 30°C, and is close to 100% humidity.
The enzymes produced by the koji mold decompose soybean proteins into amino acids, and wheat starch into glucose, producing the umami and sweetness that will become the source of what makes soy sauce delicious.

The salt is mixed in with the koji mold to make a fermenting mash.
The mash spends about six months in a tank, letting tiny, invisible organisms (yeast, lactic acid bacteria) work very hard at a slow fermentation process. The yeast creates the aromatic compounds, and the lactic acid bacteria create the sourness.
In the fermentation period, the aromatic and color compounds are produced more and more, and the taste steadily improves.

The fermented mash is wrapped in a cloth, and slowly pressed over three days by applying pressure to it.
On the first day, the mash is pressed out by its own weight. On the second day, a weak press is used. Then, on the third day, the mash is wrung out with a stronger press.
This freshly squeezed soy sauce is called "raw soy sauce" or "kiage soy sauce."
Yeast, lactic acid bacteria, and enzymes are still alive at this point.

In pasteurization, the heat balances the aroma and color, while stopping the activities of yeast, lactic acid bacteria, and enzymes to prevent a second fermentation.
The aroma of soy sauce is extremely complex. It is composed of approximately 300 kinds of aromatic compounds such as apple, rose, or vanilla.
No specific aroma is too conspicuous. The overall harmony produces the aroma unique to soy sauce.
The aroma has a spiciness that can remove the smelliness of seafood or meat, and when heated, a sweet-smelling fragrance is produced.

Filtration is an important process which removes impurities and fine leftovers of the mash in order to create the clear, liquid seasoning prescribed by the Japanese Agricultural Standards.

The soy sauce that passes inspection is packed into containers of various sizes.
It is shipped out after people visually check for problems with the containers, caps, labels, etc.

Finished soy sauce is inspected to see if it meets the standards for color, nitrogen content, salinity, and other factors.
Then, a sensory evaluation (tasting) determines the final rating. Sensory evaluations comprehensively judge color, taste, and aroma, and are carried out by sensory evaluation inspectors who have passed the qualification inspections conducted by the Japan Soy Sauce Technology Center (inc.).