Although modern machines now do some of the work, the basic method used at Hatcho Miso Company has changed little in the last 300 years. First, premium organic soybeans are washed and soaked in water for one hour. The beans are then transferred to a 200-pound-capacity cooker, steamed for two hours, then left in the closed cooker overnight.

This unusual cooking process gives Hatcho miso its deep, cocoa brown color and characteristic smoky flavor. The following morning the soft, dark beans are crushed in a special machine that shapes them into 2-inch crosses, allowing a greater surface area for the growth of micro-organisms.

Next the crosses are lightly dusted with a mixture of Aspergillus spores and toasted barley flour and incubated for 48 hours under carefully controlled temperature and humidity. As the "hatcho crosses," now called koji, emerge from the incubation room covered with a fragrant bloom of pale yellow mold and loaded with powerful digestive enzymes, the koji is mixed with sea salt and a small amount of water and transferred to seven foot tall cedar vats.
After being covered with a thick cotton cloth and the heavy wood pressing lid, the miso is pressed with a three-ton pyramid of stones, and the unhurried process of natural aging begins. The enzymes supplied by the Aspergillus slowly mellow the mixture, transforming the complex protein, carbohydrates and fats of the beans into dark, rich, flavorful amino and fatty acids and sweet simple sugars.

Finally, after at least two full years, the mature miso is scooped out with a wooden shovel. The best miso comes from deep down in the center of the vat. This was traditionally presented to the emperor who, until his recent death, enjoyed Hatcho miso soup every day. However, usually the miso is mixed together and packaged without pasteurization.

Although some manufacturers use the name Hatcho miso for their dark soybean misos, only the special miso made since the 1300's on 8th street in the small town of Okazaki is authentic Hatcho miso. The exacting ancient process gives this miso its savory aroma, mellow sweetness, and astringent flavor. According to brewmaster Kazuo Kuroda, the extreme pressure of the stones on the dry miso creates a low oxygen environment that encourages the growth of Hatcho's special type of micro-organisms. What's more, over the centuries a particular strain of Aspergillus, known as Aspergillus hatcho, has made its home in the cracks and crevices of the old seasoned vats and throughout the fermentation rooms on Hatcho Street. Aspergillus hatcho gives this miso a unique flavor that has never been duplicated by other miso makers. Hatcho miso is a cultural artifact, and more than most Japanese foods, is the authentic taste of old Japan.