Kasuzu Red Sushi Vinegar

Although rice vinegar was marketed in Japanese cities in the sixteenth century, commercial production remained small until the nineteenth century, when the sudden popularity of nigiri-zushi created a surge in demand. In response, breweries began to make rice vinegar from sake lees, the solids left over from fermenting rice to make sake. Since the new vinegar, kasuzu, was both more flavorful and less expensive than komezu, sushi chefs immediately adopted it as the vinegar of choice for sushi.

To make kasuzu, sake lees, smelling strongly of alcohol, are packed in a wooden barrel, which is sealed tightly with a paper lid and stored for two to three years. During this period, the sugars and amino acids in the sake lees react to form a brown, rich-flavored mass. This is mixed with spring water, and the mixture is left for a week. It is then stirred and strained, and half of the strained alcoholic liquid is boiled down and mixed with the rest of the liquid. The blend is left to ferment. Through natural bacterial action, the alcohol is transformed to acetic acid.