DETERMINING THE FAT-CONTENT OF MILK AND CREAM USING AC CONDUCTIVITY MEASUREMENTS

The electrical conductivity and capacitive reactance of milk and cream samples, of fat content ranging from 0.15 to 51% w/w, are reported over the frequency range 5 Hz to 200 kHz. Measurements made at 100 kHz, where electrode polarization effects are negligible, indicate that the conductivity of milk and cream increases as a near 1.7 power law of the fat-free weight fraction present. With careful temperature control and the use of a reference skimmed milk sample to correct for variations in non-fat solids and ionic composition between batch samples, for skimmed milk (0.15% w/w fat) the fat content can be determined to within +/-0.08% w/w, whilst for double cream (51% w/w fat) the maximum uncertainty is +/-0.8% w/w fat. Previous work in the literature has been restricted to a smaller range of fat contents, using measurements where the influence of electrode polarization effects could not be completely eliminated.