Arborio rice, graded superfino, is a plump, large, short-grained, Italian rice valued for its high starch content and the subsequent creaminess it brings to risotto. It is able to absorb a lot of liquid without bursting. The desirable bite in risotto is due to a defect in Arborio rice called chalk. During maturation, the starch structures at the grains core deform, making for a firm, toothy center when cooked.
There are two types of starch in rice: amylose and amylopectin. Amylopectin is a highly branched molecule that makes the rice sticky when its released from the grain during cooking. Short grain rice has the most amylopectin and little to no amylose, so its used most often for Asian cooking, when you want grains to be sticky so they are easier to eat with chopsticks.
Arborio rice is traditionally used in cooking Italian Risotto, Spanish Paella, Greek Dolmades and other Mediterranean dishes. During cooking the grains swell and absorb unusually large amounts of liquid and flavour. Stirring also gently knocks the rice grains together, releasing the surface starch on each grain. This adds to the creamy consistency of the dish, perfect for an authentic risotto. Arborio rice takes about 18 minutes to cook. It is done when it is al dente (tender on the outside and firm in the center).