Development of a device and method for the time-course estimation of low water fluxes and mean surface water activity of food products during ripening and storage

Accurate measurement of water activity (aw) is an important goal for the food industry because aw is a key parameter in microbial growth, biological reaction rates and physical properties. An experimental device was setup using air-product water balance to non-destructively estimate the time-course of mean aw at the food product surface under well-controlled airflow conditions. The device is especially suited for studying the ripening of cheeses and fermented meat products, where water fluxes exchanged between products and air are very low. The validation tests performed with aw-known model products showed that water fluxes of 10−7 kg s−1 can be estimated with an accuracy better than 2% over very short periods of time, and that surface aw can be estimated with an absolute uncertainty of less than 0.01 aw units. A handful of cheese ripening trials illustrate the potential of the method, highlighting the effects of a low air velocity and high air RH on the water exchanges occurring at a cheese surface, thus demonstrating the strong surface sensitivity to external air conditions.