Day-old rice is key to the light texture in this stir-fry (or when making fried rice). Freshly cooked rice is very moist, sticky, and clumps together (because of its high starch content). But once it has been sufficiently cooled and chilled, that starch dries up leaving each grain separated with a slightly chewy texture. Before cooking, use a fork or wet fingers to break up any clumps in the rice.