Rock sugar (冰糖, bing tang) or rock candy is crystallized sugar. It has a transparent color and tastes milder than granular sugar. It is commonly used in Chinese cooking as a sweetener and yields better cooking results than does granular sugar.
In Chinese cooking, rock sugar can be divided into monocrystal rock sugar (单晶冰糖, dan jing bing tang) and multicrystal rock sugar (多晶冰糖, duo jing bing tang).
The monocrystal type is smaller and has a regular square shape and a smooth surface. The multicrystal type usually comes in very big lumps, with a coarse surface and an irregular shape. It has a sweeter taste than the monocrystal type.
The former is usually used as a drink sweetener or candy snack, for example, in chrysanthemum tea. The latter is used in cooking, especially in soups and braised dishes. By using rock sugar, the cooked meat will have a shiny appearance and a more delicate flavor. You can always use granular sugar as a replacement if you don’t have any rock sugar.