A microwave sensor for the characterization of bovine milk

• A microwave sensor was developed for determination of water content in bovine milk.
• Over 150 samples of bovine milk, obtained from various sources were measured.
• The signal absorption is highly correlated with the solids content in bovine milk.
• The signal decrement is mainly affected by a reduction of the free water volume.
• Optimal operating temperature for real-time monitoring of moisture is around 35 °C.

The use of a moisture sensor, based on microwave absorption at 40 GHz, is explored for the direct determination of the water content in milk. The operating principle of the device is based on the relative decrement of a transmitted signal through the sample. The results of the study are based on the measurements of over 150 samples of milk, taken from individual cows, from bulk tank milk and from skimmed milk sources. A high correlation is revealed between the signal absorption, measured by the sensor, and the nominal main solids content in bovine milk, determined independently. In addition, the fat concentrations in raw milk, considered separately from the other constituents, were also well correlated to the microwave moisture meter readings. As the other solid fractions of milk show less or non-significant correlation to the absorption coefficient, it is concluded that the correlation of fat to signal decrement is due to an excluded volume effect.