Sushi vinegar, also known as "sushi-su" in Japanese, is an essential ingredient in the preparation of sushi rice. It is used to season cooked rice, giving it a characteristic flavour and a slightly acidic texture.sushi vinegar is prepared by mixing rice vinegar, sugar and salt. The exact proportions may vary according to personal preference, but generally it is used to achieve a subtle balance between sweetness, acidity and saltiness.