How MUSO's Shoyu & Tamari Are Made

How MUSO's Shoyu & Tamari Are Made

The entire soy sauce process from beginning to end is a lengthy process. It begins in fields of soybeans and wheat and may end on your dining table years later and hundreds of miles away. Soy sauce production begins in the late fall and early winter months after the arrival of the new soybean and wheat harvests. After years of experimentation, it was discovered that the fermentation process is best begun during the cold temperatures in winter.

The first step is for the soybeans and wheat to be used to prepare Koji. The soybeans are steamed until they are soft enough to be crushed easily between one's thumb and middle finger, yet remain firm enough to retain their shape. The wheat is roasted in hot sand until it turns fox brown in color and yields a fragrant aroma. Then it is coarsely milled to resemble cracked wheat. The soybeans and wheat are mixed together and inoculated with Koji-Seed.

Koji-Seed is a light green mold, known scientifically of Aspergillus group, which is widely used in Japanese fermented food products. The role of Koji-Seed is to trigger fermentation. During its growth, Koji-Seed produces proteolic, lipolytic, and amylolytic enzymes that convert proteins, fats, and starches to simpler and more easily fermentable substances.

Koji-Seed is extremely sensitive, reacting to the subtlest variations in temperature and humidity. Koji-Seed thrives best at temperatures of about 35 C (95 F), or close to human body temperature, and it prefers a humidity of about 80%.

The inoculated mixture of soybeans and wheat is incubated in a chamber called the "MURO" where temperature and humidity can be carefully controlled and easily monitored. Here the spores germinate, appearing first as small white spots on the surfaces of the beans and wheat. As the mold matures it generates its own heat and proliferates to envelop the mixture in a thin, pale yellow blanket. The Koji is taken out of the MURO at exactly noon of the third day. The matured Koji is then mixed with salt water in large cedar kegs which creates a mash known as "MOROMI."

Moromi fermentation is a complex process involving molds, yeast, and lactic acid bacteria. Enzymes released by the Koji convert starches to simple sugars. Natural yeast, including Saccharomyces rouxii further converts these sugars into alcohol and ester, which gives the soy sauce its distinctive aroma. Other enzymes, particularly diastase, break down proteins into amino acids. Then lactic acid bacteria propagate, producing lactic acids.

The fermentation process is actually far too complex to be accurately described or explained here. Different bacteria appear during the various stages of fermentation and others appear seasonally. In addition to this, certain localities have different bacterial cultures that contribute certain distinct characteristics to the flavor. The factories which make MUSO's soy sauce are located in areas reputed since long ago to be particularly suited for soy sauce production.

One of the important environmental factors is the buildings and kegs where the MOROMI is made. Many of the kegs now in use for MUSO's soy sauce are two and three centuries old, and through repeated use they retain certain microorganisms deep within the grain of the wood. Thus in addition to the traditional practices and techniques handed down within the maker's household from generation to generation; the maker's plant carries another biological tradition of microbial cultures handed down through generations of use.

The kegs are left uncovered throughout fermentation and are stirred regularly to keep the ferment active. This process helps to break up sedimentation and lumping as well as aerating the bacteria's environment. The fermentation is most active during the warm summer months and among traditional makers, aging through a second summer is considered essential to the quality and flavor of the finished product. MUSO's maker is the most prominent of a dwindling number of traditional makers still producing 18 to 24 month year old soy sauce today.

After the soy blend is fully aged, it is pressed to yield raw sauce. The raw soy sauce is then allowed to settle and clear for about one month, during which time oils are skimmed off of the surface, remaining solid proteins are broken down, and coarser sediments are drawn off from the bottom.

Finally the cleared soy sauce is heated at 80C (176F) for one hour. The heating of the soy sauce is also a traditional practice handed down over many generations. Care is taken in this heating process not to destroy the valuable enzymes and other nutritional properties of the finished product, while at the same time heating the sauce enough to kill the working bacteria in order to assure the long life of the finished product. Care taken at this time assures not only the stability of this soy product but also contributes to the exquisite flavor and aroma of MUSO's soy sauce.


Fermentation process

Soy beans       Brown rice Koji


The Kegs

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