Bean jelly is a traditional folk snack, made of starch, which is made of starch in wheat flour. Although cold noodles are made of flour, they are not made of flour directly. If we look at flour from the perspective of bean jelly, the main components of flour are starch and gluten, so to make bean jelly, we must first separate starch from gluten, and then use the obtained starch to make bean jelly. The way to separate gluten from starch is to wash your face. This is why you have to wash your face when cooking cold noodles. After washing your face, flour is divided into two parts, namely gluten and starch. White material in the flour water is starch, and the gluten left in the basin is gluten. The freshly washed starch can't be used to make cold noodles immediately, mainly because the noodle water is too thin, and the cold noodles can't be formed and must be precipitated. Because the specific gravity of starch is greater than that of water, after standing for several hours, starch sinks, which is obviously related to the moisture layer. Although cold rice noodles are made of starch, not all starch can be used to make cold rice noodles. There are many kinds of starch, but their uses are different. For example, pea starch is most suitable for bean jelly, and sweet potato starch is most suitable for vermicelli. Similarly, wheat starch is most suitable for cold rice noodles, and no other starch can make the unique soft, bright, smooth and firm quality of cold rice noodles.