One of the few remaining authentic tamari shops is Mitoku's producer, Minamigura Aoki Yaemon Company, founded by the Yaemon family in 1871. Located on the Chita peninsula in the Aichi prefecture, the Yaemon shop is a virtual tamari and soy miso museum. Inside the old wooden storehouse, rows of towering 100-year-old wooden casks, held together with huge hoops of braided bamboo, are filled to capacity with 30,000 pounds of thick, rich tamari. The air is filled with the heady aroma of fermenting soy sauce, and, if you listen carefully, you can hear the sound of bubbling brew, particularly on hot summer nights.

Yaemon has been a Mitoku supplier in the past, but recently became Mitoku's main producer. Mansan Tamari, made by the Oguri family, Mitoku's producer of tamari in the past, decided to close their shop because no one in the family was available to continue the tradition. Yaemon, who is a distant relation to Oguri and uses the same ancient traditional process, has agreed to take over for Oguri and become Mitoku's main supplier. All of the Mansan aging tamari and vats have been transferred to the Yaemon shop. Although the Yaemon family has bought some new equipment for washing, cooking, and mixing, fourth-generation president Yoshio Yaemon still uses the traditional recipe and techniques of his forefathers. Whole natural ingredients, hand-made soybean koji, a high ratio of soybeans to water, and long, natural aging in wood are still his company's proud hallmarks.

In the fall, when natural conditions are ideal for making koji, the Yaemons begin each day by soaking one thousand pounds of choice organic soybeans in well water. The next morning, the swollen beans are placed in a one-ton capacity steamer. After cooking, the soft beans are crushed into tiny balls (about 5/8 inch in diameter) called miso dama. These balls are dusted with a mixture of Aspergillus spores and roasted barley flour and then placed in a special room to incubate for about 3 days. During this time, Yaemon carefully controls the temperature and humidity. (According to Yoshio Yaemon, before the advent of laboratory methods to isolate Aspergillus, balls of cooked soy beans were hung out to be naturally inoculated by wind-blown Aspergillus spores.) The sweet smelling, fluffy, pale yellow balls, now called koji, are removed from the incubator and placed on bamboo mats to dry for two weeks. The Yaemon shop is the only tamari company that uses this unique koji drying process. According to Yoshio Yaemon , this process is responsible for Yaemon tamari's extra thick, rich quality and concentrated flavor.

The dried koji is mixed with a brine solution (sea salt and water) and placed in ten-foot-tall cedar vats to ferment. This fermenting mash, called moromi, is actually a thick paste that, like miso, is pressed with 1,000 pounds of river stones.

During the long aging process, enzymes from the Aspergillus culture in the koji and naturally occurring yeasts and bacteria, which inhabit Yaemon's old storage building, slowly break down the moromi. The complex carbohydrates, proteins, and oils of the soybeans are transformed into sweet sugars, aromatic alcohol, and flavorful amino and fatty acids. The mature fermented moromi is then placed in cotton sacks and pressed under great force to extract its dark liquid, a mixture of tamari and crude soy oil. The oil, which rises to the surface, is removed. The tamari is finally ready for settling and bottling. Yaemon Tamari contains no preservatives. Mikawa mirin (rice brandy) is added as a natural preservative. The entire process takes about eighteen months.