Sushi rice is a preparation of rice — typically a short-grained, white Japanese rice — commonly used to make sushi. It is usually mixed with sugar, salt, and rice vinegar, and may also include kombu and sake. The rice used in sushi is sometimes made with a combination of this and other types of rice, and even with wild rice.
Rice is, itself, an essential part of sushi, and in many ways is the defining feature of this dish. The most classic type of sushi, nigiri-zushi, is simply a mound of pressed sushi rice with fish on top of it. Nigiri-zushi may include nori seaweed in a thin strip around it, especially pieces made with squid or eel. The most common type of sushi found in the west, however, is maki-zushi. Maki-zushi consists of rolls of rice wrapped with nori seaweed either on the inside or the outside, and some sort of filling.
Sushi rice must be quite sticky to function as required. This is especially true in dishes such as uramaki, where the rice is on the outside of the nori, and so must cling to it. Good rice should have a level of stickiness where all of the grains stick firmly together, but it should not be so sticky that it becomes an amorphous mash of rice. Because long-grained rice tends to be fairly dry, it is not appropriate for use in sushi, since the lack of moisture makes it insufficiently sticky. Short-grained rice is wet enough that, when properly prepared, it sticks together well.
To cook sushi rice, a chef prepares the Japanese rice as usual, cooking it and letting it steam for a while. The sauce is then prepared, mixing the sugar, salt, and rice vinegar together in a bowl. The sugar should be fully dissolved on a low heat, and then the mixture should be allowed to cool. The steamed rice, while still hot, should then be spread out in a large wooden or ceramic bowl, or on a large plate. The sauce is then drizzled on top of the rice, and it is quickly folded over itself. For particularly shiny rice, a fan can be set up to cool and dry it as the sauce is being mixed in.
The mixture of the sauce itself is what makes different sushi rice preparations. At its most basic, 3 cups (558 grams) of dry rice would use about 1 teaspoon (6 g) of salt, 3 tablespoons (37.5 g) of sugar, and 0.33 cup (78.8 ml) of rice vinegar. Different regions have their own versions of this recipe. For example, in Tokyo, 2 teaspoons (12 g) of salt might be used, while in Osaka, 4 or even 5 tablespoons (50 or 62.5 g) of sugar would be used, resulting in much sweeter rice. Some regions also add little pieces of dried kombu seaweed, or small amounts of Japanese rice wine, sake, to spruce up the recipe a bit.