When you say red rock candy, you should mean the so-called old rock candy, which is polycrystalline rock candy made by traditional techniques. White rock candy or single crystal rock candy and polycrystalline rock candy are all made of hot refined saturated sugar solution, but the crystallization process is different. However, it has been reported that ordinary single crystal rock candy must be bleached by sulfur dioxide and can be eaten within the specified range. However, it is better to eat less single crystal rock candy that is too transparent and too white in color.