Preserved fruit is a traditional sugar product in China. First, it has high nutritional value and is crystal clear. It is a diamond product for friends and relatives, old and young Xian Yi. In the process of processing, selling and storage, a layer of white product often appears on the surface of preserved fruit, which is the so-called "sand returning" phenomenon of preserved fruit. Once the preserved fruit "returns to sand", it will not only affect the appearance quality of the product, but also reduce the sugar content of the product after crystallization, which will reduce the nutrition and make it difficult to preserve. First, the main source of "returning to sand" of preserved fruit: 1. Sugar monosaccharide is one of the main raw materials for processing preserved fruit. It has the property that when a sugar exists alone, it is easy to crystallize. Therefore, it is easy to cause the phenomenon of "sand return" of preserved fruit by using only one kind of sugar. 2. In the process of processing, if the sugar concentration of fruit raw materials exceeds 45% when boiling sugar for the first time, because of the high viscosity of sugar solution, the gun can't go deep into the fruit as soon as possible and accumulate on the surface layer, resulting in dry shrinkage, hard outside and soft inside, and crystallization on the surface. This phenomenon is also called "sugar heart". In the whole process of boiling sugar, if the concentration of sugar solution is greater than the solubility of sugar, the product will also "return to sand", especially when stored below 10OC. 3。 Sucrose is over-converted, and preserved fruits are often lined with sugarcane. During processing, if fruit and sucrose are heated together under acidic conditions for a long time, sucrose will be excessively converted into glucose and fructose, which will lead to the crystallization of chrysanthemum grapes, and the sugar content is greater than its solubility at room temperature.