In Japan, a blue fin tuna is graded by the quality of the cuts of meat which can be obtained from it, particularly the prized toro, the fatty belly of the tuna. Tuna for sushi is carefully handled, to ensure that the flesh is not bruised or damaged. When the tuna arrives at the fish market, core samples of the flesh are taken with a special tool so that the color, texture, and flavor of the meat can be assessed before the tuna is priced. While sushi uses many different types of tuna including yellow fin and big eye, true toro is only taken from blue fin tuna.
Toro comes from the underbelly of the tuna, and is itself divided into grades which are distinguished based on the marbling of the meat, much like in grading beef. The most valuable toro, otoro, is from the underside of the fish close to the head. Chutoro, a lesser grade, comes from the belly in the middle and back of the fish, and is less marbled than otoro.
The unmistakable and delightful flavor of toro seduces most consumers once they try it. The cool, meaty texture of raw tuna combines with the fat of the belly to create a buttery sensation in the mouth, with the flesh of the tuna melting as you eat it. Toro is often used in sashimi and nigiri sushi, because the delicate flavor, outstanding texture, and beautiful marbling are clearly distinguishable in these two raw fish dishes. It is also sometimes used to make seared rare tuna, which has a delicious warm grilled exterior and a creamy cool interior.
A high quality piece of toro will be pale pink with rich white streaks. Otoro has more of the fatty streaks, which lend toro its unique and spectacular flavor. Chutoro is less veined with fat, although it is still more fatty than cuts from the upper side of the fish, such as akami. Toro is most flavorful during the winter, when tuna accumulate more fat, and may not be as spectacular out of season. It should also always be eaten fresh, as it does not stand up well to prolonged freezing.
Astoundingly, toro is not widely eaten outside of Japan, although it is sometimes available in specialty Japanese restaurants on the coasts of the United States and in some parts of Europe. Toro plays a delightful role in Japanese cuisine in Japan, and the majority of blue fin tuna harvested around the world end up in the fish markets of Japan, where the toro and the rest of the fish will command a higher price among connoisseurs.