Moisture sorption isotherm
Encyclopedia
At equilibrium, the relationship between water content and equilibrium humidity of a material can be displayed graphically by a curve, the so called moisture sorption isotherm.
For each humidity
value, a sorption isotherm
indicates the corresponding water content
value at a given, constant temperature. If the composition or quality of the material changes, then its sorption behaviour also changes. Because of the complexity of sorption processes, the isotherms cannot be determined by calculation, but must be recorded experimentally for each product.
The relationship between water content and water activity
(aw) is complex. An increase in aw is usually accompanied by an increase in water content, but in a non-linear fashion. This relationship between water activity and moisture content at a given temperature is called the moisture sorption isotherm. These curves are determined experimentally and constitute the fingerprint of a food system.
For each humidity
Humidity
Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...
value, a sorption isotherm
Sorption isotherm
A sorption isotherm describes the equilibrium of the sorption of a material at a surface at constant temperature. It represents the amount of material bound at the surface as a function of the material present in the gas phase and/or in the solution...
indicates the corresponding water content
Water content
Water content or moisture content is the quantity of water contained in a material, such as soil , rock, ceramics, fruit, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 to the value of the materials' porosity at...
value at a given, constant temperature. If the composition or quality of the material changes, then its sorption behaviour also changes. Because of the complexity of sorption processes, the isotherms cannot be determined by calculation, but must be recorded experimentally for each product.
The relationship between water content and water activity
Water activity
Water activity or aw was developed to account for the intensity with which water associates with various non-aqueous constituents and solids. Simply stated, it is a measure of the energy status of the water in a system...
(aw) is complex. An increase in aw is usually accompanied by an increase in water content, but in a non-linear fashion. This relationship between water activity and moisture content at a given temperature is called the moisture sorption isotherm. These curves are determined experimentally and constitute the fingerprint of a food system.