Chaga is traditionally grated into a fine powder and used to brew a beverage resembling coffee or tea. For medicinal use, an extraction process is needed to make at least some of the bio-active components bioavailable. These bio-actives are found in the mostly indigestible chitin cell walls of the chaga. Humans lack the enzyme chitinase, so cannot fully digest raw mushrooms or their derivatives, and the digestive process works too fast for the stomach acid to take effect. Scientific studies and research are in general also based on highly concentrated extracts, and traditional Russian usage is also based on a form of hot-water extraction (by preparing zavarka).