Rice steamingRice steaming is one of the most important steps of vinegar making. We use polished white rice for regular komezu or rice vinegar, and unpolished rice for kurokomezu or black vinegar. We place pre-soaked rice in a large vat called koshiki to steam the rice, a very delicate process which requires the preparation of rice at a perfect moisture level.
Sashiyu - adding of water
For unpolished grain of rice to become fluffy, we add boiling water during the steaming. It creates a large amount of steam rises from the koshiki filling the place with a nice aroma unique to the rice cooking.
Kai - stirring
We place ingredients such as fluffy steamed rice, vinegar starter, spring water from Mont Nachi in kioke. We use a large wooden oar called a kai to stir and mix the contents just like rowing a boat.
The yeast found in the outer layer of unpolished rice grain breaks down starch into sugar, and sugar into alcohol. Acetic acid is produced by the bacteria that have lived in the walls of brewery and the grains of kioke and forms a thin film on the surface to gradually brew vinegar underneath by the oxidation of ethanol.
Natural fermentation gradually progresses for about 45 days during winter and 70 days during summer. During the fermentation stage, we need to keep the temperature within the kioke around 40℃ therefore we adjust the temperature by placing the cover called komo around the kioke during winter. The fermentation is advanced faster due to the thermal turbulence caused by the difference between interior and exterior temperature during winter. Once the fermentation is complete we replace the content into a different kioke for maturation up to 4 to 5 months.
Pasteurization, bottling and inspection.
Matured vinegar is pasteurized by heat then bottled. Each and every bottled product goes through a visual inspection to make sure all products are free from impurities before dispatching.