Malt diastase is often used in conjunction with the PAS staining procedure to specifically identify glycogen granules in tissue samples. Amylase enzymes in the malt extract are used to digest the glycogen into smaller sugar units, which are then washed out of the tissue sample with water.
It is standard procedure to section two serial sections and perform the staining process at the same time. One tissue section is treated with diastase to digest the glycogen, followed by a water rinse. The other section is left untreated and is held in water. Both sections are then stained with the PAS procedure for comparative microscopic analysis. Staining that is lost following the digestion procedure is indicative of glycogen.