rae kirk wrote:We bought some food grade DE years ago. Was wondering if it has a shelf life?
Being an inorganic oxide (SiO2), it will probably outlast any shelf it is sitting on. There are no chemical reactions that could decompose it, and the only physical process would be to subject it to heat and pressure, like that found at a subduction zone at the edge of a continental plate. That kind of heat and pressure, for a long enough time, and it could metamorphosize into a denser crystal structure. It has no nutrients to support bacterial life, so as long as it is in a sealed container, it should remain sterile and free of any pathogens.