digester n : autoclave consisting of a vessel in which plant or animal materials are digested

A digester is a device used in papermaking which takes small wood chips, and cooks them for a number of hours, to remove lignin. The softer chips are then passed on to a machine that bleaches them to the desired degree of whiteness.

An anaerobic digester is a device used to harvest biogas, a gas largely comprised of methane to supplement conventional energy sources, from organic waste. These digesters, or biodigesters, are made in various ways, using a wide variety of organic materials available (cattle manure, human feces, or plant-based waste). The style of biodigester depends largely on the building materials and waste products available to the user, as well as the energy needs he/she may have.