Case hardening is a drying defect in which the outer surface of a food product dries and hardens too rapidly, trapping residual moisture in the core and compromising storage stability and microbial safety.
In trade practice
The defect occurs when surface evaporation outpaces internal moisture migration, typically caused by excessive temperature or airflow in the early drying stage. QA teams detect it by measuring water activity at the core versus the surface, or by observing a leathery exterior with a soft centre on cut inspection. Prevention relies on staged drying profiles with moderate initial temperatures and controlled humidity, validated during process commissioning and monitored in production records.
In a specification
A dried-product specification should define the maximum permitted water activity for the finished product and require that the supplier’s validated drying profile is available for audit, as indirect evidence that case hardening risk has been controlled.