Water-Activity Meters and Sampling

A water-activity meter measures equilibrium relative humidity above a sample and expresses it as water activity at a stated temperature. It measures water availability rather than total moisture.

Chilled-mirror, capacitance and electrolytic sensors have different response, range and contamination sensitivity. The instrument should suit the expected product values and required decision.

Sampling location must reflect the process question. Whole-muscle centres, sausage cross-sections, surfaces and packaged equilibrated products can have different water activities.

Sample and chamber temperature should be controlled, and the reading allowed to stabilise. Condensation or temperature mismatch can produce false results.

Check the meter with suitable standards that bracket or cover the working range. Salt, fat, volatiles and residue can contaminate sensors and sample wells.

Record sample identity, location, temperature, instrument and result. Weight loss may correlate with water activity only after product-specific evidence establishes the relationship.