The maximum equilibrium moisture content describes the active behavior of a hygroscopic material (product or packaging).
Hygroscopic materials release water vapor until the surrounding air exhibits a relative humidity corresponding to the equilibrium moisture content of the material. Each material has its own wholly specific equilibrium moisture content.
As water vapor is released, the water content of the material diminishes and the water content of the air rises, i.e. the material dries out. A continual supply of fresh air, which has a relative humidity which is lower than the equilibrium moisture content, would cause the material to release ever more water vapor (shrinkage). The eventual consequence of this would be, for example, that fruit would increasingly dry out and diminish in quality. It must therefore be ensured that air in the system is not too dry, so as to prevent excessive drying-out.
Conversely, supplying air which is too moist may, for example, lead to the onset of spoilage or corrosion of goods due to excessive humidity or the absorption by corrugated board packaging of moisture from the ambient air, making it damp and causing it to lose its stability. This then causes problems where several cartons are stacked on top of one another, since the cartons at the bottom are no longer able to withstand the stacking pressure and so collapse.
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