An apparatus for detecting physical abnormalities in milk which comprises a light source for irradiating milk with light of red or green or blue colors or any combination of such colors. The intensity of light reflected or diffused or transmitted, or any combination thereof, by the milk, or from background light of the milk, is measured by light sensors. A computer processes the measurement data and is programmed to select, based on comparisons of the values derived from the measured light intensities with reference values, a diagnostic basis or diagnostic bases for abnormalities in the milk from a plurality of diagnostic bases of possible abnormalities stored in the memory of the computer.