Rock candy is made by melting white sugar into liquid, firing, removing impurities, and then evaporating water to make it crystallize naturally at about 40℃, or freezing and crystallizing.
Good quality rock candy is even white or yellow, translucent, with crystal luster, sweet texture, no odor and no obvious impurities. The quality of yellow rock sugar is poor.
People should use clear white rock sugar when eating nutritious food.