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 +or-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.