Moisture content

Moisture content is the amount of water in a material, commonly expressed as a proportion of its mass. It can be reported on a wet basis or a dry basis.

Gravimetric analysis: A quantitative method that determines a substance’s amount by measuring mass. Drying a sample to constant mass is a direct way to determine its water fraction.
Wet-basis moisture content: Water mass divided by the total mass of a moist material. This convention expresses moisture as a fraction of the sample as received.
Food preservation: Methods that slow food spoilage and extend the time food remains usable. Drying lowers moisture in foods, but water activity better predicts microbial growth.
Relative humidity: The ratio of air’s water vapor pressure to its saturation vapor pressure at a given temperature. It describes moisture in air, whereas moisture content describes water within a material.
Karl Fischer titration: A chemical titration that measures water through its reaction with iodine and sulfur dioxide. It quantifies water directly when simple drying could also remove other volatile substances.
Dry-basis moisture content: Water mass divided by the mass of the material after its water is removed. Dry-basis values use dry solids as the denominator and can exceed 100 percent.
Grain drying: The removal of water from harvested grain to improve storage stability. Moisture content guides drying targets that reduce spoilage without damaging grain.
Volumetric water content: The volume of water in a material divided by the material’s total volume. It uses volume rather than mass and is especially useful for measuring soil moisture.
Loss on drying: A test that estimates volatile content from the mass a sample loses during drying. It is a common proxy for moisture content, though the lost mass may include substances besides water.
Mass fraction: A component’s mass divided by the total mass of a mixture. Moisture content is often reported as a mass fraction, with the chosen denominator specified.

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