Manufacturing Process
Each factory processes approximately 80 tons of sweet potatoes per day, amounting to a total of around 400 tons across five factories. During the harvest season from August to December, fresh sweet potatoes are delivered daily.
After the soil is removed and the sweet potatoes are carefully washed, they are sorted by hand. Any imperfections are carefully trimmed by hand.
In making sweet potato shochu, rice is used to create koji. Steamed rice is inoculated with koji mold and allowed to grow for about two days. The enzymes produced by the koji mold break down the starch in the rice and sweet potatoes into sugar.
Primary (first) fermentation involves creating the primary mash, known as shubo (the mother of sake). In the primary fermentation tank, koji mold and Kirishima Rekka-sui are added, followed by yeast. The enzymes from the koji mold break down the sugars, which the yeast then uses as a food source to multiply and produce alcohol and carbon dioxide. After about five days, the primary mash is complete, with an alcohol content of approximately 14%.
The sweet potatoes are continuously steamed for about an hour in a steamer until the core temperature reaches 91°C, making them ready for fermentation. After steaming, they are gradually cooled on a conveyor.
Secondary fermentation involves adding sweet potatoes and Kirishima Rekka-sui to the primary mash, creating the secondary mash that forms the base for sweet potato shochu. The starches in the sweet potatoes undergo saccharification, leading to the production of alcohol through fermentation. Both saccharification and alcohol fermentation occur simultaneously within the same mash (a process known as parallel fermentation). After approximately eight days, a secondary mash infused with a subtle sweet potato aroma is produced.
Distillation is the process of boiling the secondary mash to produce alcohol vapors, which are then cooled to extract shochu with concentrated flavors. The alcohol content is high at the start but gradually decreases, resulting in sweet potato shochu with an alcohol content of about 37%. This shochu contains hundreds of trace elements, including high-quality fatty acids, which contribute to its flavor. The interaction of these elements creates the complex taste of sweet potato shochu.
Distilled spirits, known as aquavit in Latin, meaning "water of life," trace their origins back to the Mesopotamian civilization around 3000 BC. In addition to the commonly used vertical stills, Kirishima Shuzo employs its own unique horizontal still, the Enatsu-type E-II still, which was designed and developed by the company’s second president, Junkichi Enatsu.
Aging is the process of mellowing the rough, freshly distilled spirit over a long period of time to impart roundness. By aging, the balance of sweetness, richness, and roundness is refined. The aging method and duration vary depending on the product, but it typically takes several months to several years.
Blend
Blending is the process of recognizing the unique characteristics of each shochu in the aging tanks and carefully combining them in the right proportions to create a single product. Shochu is a "living entity," with its flavor subtly changing based on the ingredients, seasons, and daily climate. Skilled blenders use their finely tuned senses to assess each shochu's individual qualities, and by blending them in the ideal ratio, they ensure the product maintains consistent, high-quality flavor year-round.
Junkichi Enatsu continuously researched to achieve a truly satisfying taste, and as a result, he established Kirishima Shuzo's unique standards of sweetness, richness, and roundness. These three standards continue to be passed down to the blenders at Kirishima Shuzo to this day.
Bottling &
Packaging
After blending and diluting the shochu, it is automatically filled into various sized and shaped bottles using a filling machine. The filled bottles then undergo rigorous inspection using both a liquid inspection machine and visual inspection.
