Diatomaceous Earth (DE), a chalk-like sedimentary mineral that is derived from fossilized shell-like remains of marine alga called diatoms. It is also commonly referred to as kieselgur or diatomite. The shells are extremely fine and generally range in length from 40 to 160 μm and in width from 2 to 5 μm, the latter being roughly the diameter of most yeast cells. Because of their microscopic size and porous nature, DE preparations have been used extensively in the brewing industry as a filtering medium.
There are two types of diatomaceous earth, one derived from saltwater and the other from fresh water and the material is mined throughout the world. In the brewing process, the saltwater variety of DE is often used for filtration. DE filters for brewing fall into two categories: pressure leaf filters and sheet filters. These filters are used to clarify beers by trapping yeast and other particulates. DE is available in various grades, with finer grades capable of tighter filtrations. Fresh water DE is often used as a natural pesticide and can help protect grain stores from infestation.
DE has held many functions since it was first used by the ancient Greeks as a building material. Alfred Nobel used DE as a stabilizer for the nitroglycerine he used to make dynamite.
Typically off-white in color, DE resembles talcum powder and is composed of up to 90% silica, with the remained consisting of alumina and hematite.
DE can be dangerous if inhaled and caution is advised when handling the substance. Exposure can cause irritation to the lungs and eyes and prolonged exposure has been linked to severe respiratory problems. Given the health risks associated with DE, the disposal of postfiltration DE is becoming increasingly more regulated.