This layer of frost is a crystal synthesized by kelp itself, which will be displayed after low temperature or air drying. Its name is mannitol.
Mannitol is beneficial to the body and has high edible and medicinal value. It is low in calories and is often used as a sweetener for foods needed by diabetics, bodybuilders and dieters. Mannitol also has diuretic effect. So when many people choose dried kelp, they will choose kelp with frost, because this kind of kelp has higher nutritional value and will be more nutritious than kelp without frost. And if you don't like this substance, it's easy to clean up, because this hoarfrost is soluble in water, and white material on the surface of dried kelp can be removed by soaking it in water for a period of time.