Humins are a class of organic compounds that are insoluble in water at all pH's. The term is used in two related contexts, in soil chemistry and saccharide chemistry. These dark brown solids are inhomogenous and their structures are often vaguely described.
Soil consists of both mineral (inorganic) and organic components. The organic components can be subdivided into fractions that are soluble, largely humic acids, and insoluble, the humins. Humins comprise about 50% of the organic matter in soil.
Humins also produced during the dehydration of sugars, as is conducted in the conversion of cellulose to smaller organic compounds. These humins arise by the condensation of sugars with furfural and hydroxymethylfurfural, products of the dehydration of pentoses and hexoses. Since they are generally undesirable for chemical purposes, efforts are made to avoid their formation. Otherwise, humins are used for fuel.
Criticism
Humic substances, including humin, have not been observed in soils using modern analytical techniques.