The key to making great fried rice, with individual kernels of rice intermingled with eggs and vegetables is to use cold, leftover rice. This is because of the molecular changes that happen to the starch molecules during the cooking and subsequent cooling process.
According to On Food and Cooking by Harold McGee, Starches, which are mainly made up of glucose (sugar) molecules strung together, are a plants way of storing extra energy. The two main starch molecules used by plants to store energy are amylose and amylopectin. The difference between amylose and amylopectin is that amylose is mostly a linear molecule (imagine a chain) while amylopectin is highly branched. A typical amylose molecules in made up of about 1,000 glucose molecules, while a typical amylopectin molecules is made up of about 5,000 – 20,000 glucose molecules.
A plant stores amylose and amylopectin tightly packed in structures called starch granules. During the cooking process, the plants orderly arrangement of amylose and amylopectin is disrupted, creating a mesh like structure of the two molecules. This mesh is the result of water molecules being absorbed during the cooking process and making the grains expand and soften. The cooling process to some extent reverses that mesh like structure into something that does not resemble either the original orderly arrangement of the starch molecules or the mesh, but something in between, with many of the water molecules once again pushed out from in between amylose and amylopectin. The change that occurs during the cooling process called retrogradation and results in what are called resistant starches. Another example of retrogradation happens when bread cools down after baking.
What keeps the rice kernels from clumping up while making the stir fry is the loss of water and the molecular changes that the starch molecules undergo during the process of retrogradation.