What ingredient is added to sushi rice to give it a sweet and sour flavor?

The ingredient added to sushi rice to give it a sweet-and-sour flavor is rice vinegar. In Japanese cooking, cooked rice for sushi is typically seasoned with vinegar, sugar, and salt, creating the balanced tang and slight sweetness associated with sushi rice.

Japanese rice vinegar is relatively mild and mellow, with about 5% acetic acid. It is made from rice or sake lees and is softer in flavor than many Western distilled vinegars. Prepared seasoned rice vinegar, sometimes called awasezu, already contains sugar and salt, making it convenient for sushi preparation.

Rice vinegar is not the same as rice wine or mirin. Mirin is a sweet rice-based cooking alcohol and may appear in some Japanese seasonings, but it is not the standard vinegar responsible for sushi rice’s characteristic acidity. Different sushi traditions also use different vinegars: Edomae-style sushi historically used akazu, a reddish vinegar made from aged sake lees.