Microwave Drying to Determine the Solids Content of Milk and Cottage and Cheddar Cheese

Microwave ovens have been used in quality control laboratories for rapid determination of moisture content of dairy products. Factors that influence sample drying rate and final test result for microwave drying are quite different than factors that influence conventional drying methods. Differences in dielectric properties of samples will have a significant influence on microwave drying, but may not influence conventional drying. Sample handling methods that reduce variability in test results for milk, cottage cheese, and Cheddar cheese are discussed. Preliminary investigations indicated that there are differences in results from one microwave oven to the next, even when the same sample material was dried under the same analysis conditions. This variations may be due to a combination of differences in sample positioning, differences in wave patterns in individual oven cavities, and differences in magnetron power output with age and heavy usage. Good correlations of microwave test results with those from the standard method were obtained for milk and cottage and Cheddar cheese. Statistically significant differences between microwave results and standard method results indicated that for best agreement between laboratories it would be necessary to calibrate individual microwave ovens against a standard reference method for each type of product.