Japanese white rice vinegar is a mild, clear vinegar produced through the two-stage fermentation of rice starch into alcohol and then into acetic acid, and it is a foundational seasoning in Japanese cuisine. Known in Japanese as komezu (米酢, “rice vinegar”), the term combines kome meaning “rice” and su (酢) meaning “vinegar.” Japanese white rice vinegar developed alongside wet-rice agriculture and sake brewing traditions, as acetification of rice alcohol became a natural extension of grain fermentation technologies. It is most strongly associated with Japan, though it shares technical roots with broader East Asian vinegar-making practices.

The production of Japanese white rice vinegar begins with polished rice, typically from Oryza sativa subsp. japonica, whose starch is saccharified using koji mold (Aspergillus oryzae) to convert starches into fermentable sugars. Yeasts then ferment the sugars into ethanol, after which acetic acid bacteria—most commonly species such as Acetobacter pasteurianus—oxidize the ethanol into acetic acid under aerobic conditions. Compared to Chinese black rice vinegar, Japanese white rice vinegar is lighter in color, lower in acidity (generally around 4–5%), and has a subtly sweet, clean flavor profile. Some varieties are naturally brewed and aged, while others may be blended for consistency. Seasoned rice vinegar (awase-zu) contains added sugar and salt and is specifically formulated for sushi rice.

Culinarily, Japanese white rice vinegar is indispensable in sushi preparation, where it is mixed with freshly cooked rice to create the characteristic balance of acidity, sweetness, and aroma that defines modern sushi. It is also used in sunomono (vinegared salads), quick pickles (tsukemono), dipping sauces, dressings, and certain simmered dishes where gentle acidity is desired without overpowering other flavors. Its development was pivotal in the evolution of Edo-period sushi, in which vinegar-seasoned rice replaced older forms of lactic fermentation as a preservation and flavoring method.