The amount of inorganic material in biomass, either structural or extractable, should be measured as part of the total composition. Structural ash is inorganic material that is bound in the physical structure of the biomass, while extractable ash is inorganic material that can be removed by washing or extracting the material. Extractable ash can be the result of soil remaining in the biomass. Refer to LAP “Total Mass Closure” for information on where to utilize this procedure.