HUMIDITY AND MOISTURE MEASUREMENTS IN FOOD PROCESSING APPLICATIONS

In the framework of the EMPIR Project 14IND11 HIT (Metrology for humidity at high temperatures and transient conditions), a method for estimating in real time the water loss in a hazelnuts roasting process, through humidity measurements, and its correlation with food quality parameters was demonstrated in an industrial application. At the industrial plant of a manufacturer of food processing systems, two separate measurement setups were designed and implemented on laboratory-scale roasting ovens, based on infrared and hot-air heating, in order to estimate both the water loss and the volume temperature distribution in real time during roasting tuning processes. In such a roasting process, air temperature and dew point temperature were associated with the detailed roasting protocol which in turns produces different quality of the final processed product. To perform such in-process measurements, the above quantities were measured by several PRTs and by a chilled-mirror hygrometer at temperatures between 120 °C to 180 °C and dew-point temperatures up to 35 °C, respectively. This work reports on the measurement set-up, the details about preventing volatile organic contamination of the chilled-mirror hygrometer and the validation of real-time humidity measurements by comparison against a gravimetric (water-loss) method. Suitable data processing methods of humidity measurements were implemented in order to the estimate water loss from dew-point measurements and correlate it with selected food-quality parameters. The overall results of the study are presented.