Disclosed is a fresh-keeping period determination method. A fresh-keeping period is less than 1/2 of a shelf life and is most preferably 1/3 of the shelf life. The method comprises: dividing a preservation time of fresh milk into a plurality of short enough time periods, so that a change in the electrical conductivity in the time periods can be ignored, according to the detected electrical conductivity of the fresh milk in the time periods or other parameters related to temperature, reducing the time periods to a preservation time at a standard preservation temperature, and determining whether the sum of the reduced time periods is greater than a fresh-keeping period at the standard preservation temperature, and if so, determining that the milk exceeds the fresh-keeping period, and if not, determining that the milk is in the fresh-keeping period. The reduction is made on the basis that the ratio of deterioration speeds at different temperatures is equivalent to a reciprocal of the ratio of time used for achie
