Overdrying

Overdrying refers to the excessive removal of moisture from a material during a drying process, driving its water content below the intended target or below its equilibrium moisture content. It can occur in many contexts, including food processing, textiles, pharmaceuticals, and wood drying.

Causes include prolonged drying times, use of high temperatures, low humidity, aggressive airflow, and inadequate process control or monitoring. In some systems, moisture gradients within a material can lead to continued drying even after surface moisture has been removed, contributing to overdrying.

Effects vary by material. In foods, overdrying can cause hard, brittle textures, reduced solubility and rehydration quality, and losses of flavor and nutrients. In textiles, overdried fibers may become stiff, brittle, or prone to cracking and shrinkage. In wood, excessive drying can cause warping, checks, or case hardening, reducing dimensional stability. In pharmaceuticals, overdrying may degrade active ingredients or alter tablet compression and dissolution properties.

Prevention and detection involve monitoring moisture content or water activity and using equilibrium moisture content curves to set end points. Inline moisture sensors, regular sampling, and controlling drying temperature, humidity, and airflow help prevent overdrying. It is also important to balance energy use with product quality, as overdrying wastes energy and can reduce overall yield or functionality.

Overdrying is generally undesirable because it can degrade product quality, increase brittleness, reduce rehydration capacity, or compromise performance in end-use applications.