Have you ever made rice that was perfectly fluffy and then the next day, taken it out of the fridge only to find it hard and crumbly? The secret to this culinary transformation is starch, specifically the difference between amylose and amylopectin.
Most starchy foods contain some balance of the two starch types, which differ in their structures. Amylose connects to other molecules in long chains while amylopectin connects in more of branch-shaped structure. Foods with fluffy textures such as long-grained rice contain more amylose, while sticky or waxy foods like arborio rice contain more amylopectin.
As starchy food cooks, the linked starch molecules begin to relax. As they relax, water is able to come in between the links, making the foods softer, easier to digest, and more enjoyable to eat. Scientists call this process gelatinization. It is gelatinization that explains the dramatic texture change in starchy foods. For example, when long-grained rice cooks, it turns fluffy because the starch in it gelatinizes at a high temperature meaning that by the time you eat it, some starch molecules are still intact. Arborio rice, however, has more amylopectin, so starch gelatinizes at a lower temperature, meaning that by the time you eat it, a lot of the starch molecules have burst, creating gooey, creamy cohesion of foods like risotto.
As the gelatinized starches cool, however, they begin to reform a different state with less crystalline structure, leading to what’s called starch retrogradation. The amylose in the cooked long-grained rice turns it hard rapidly as the starch molecules recrystallize. In contrast, the dispersed amylopectin reforms at a much lower rate, allowing you to enjoy arborio rice’s texture longer.
