Random sampling was carried out on 70 samples of raw milk obtained from one of the Tehran's milk pasteurization plants. Acidity and freezing points (F.P.) of milk were tested on the first day and after seven days of refrigeration. To titre milk acidity, decimal NaOH method was used and F.P. was determined by cryoscope (Cryotest model, Gerber comp.).
It was seen that the percentage of samples which had F.P. above -0.53°C decreased from 42.85% to 15.71% after seven days and percentage of those which had F.P. less than -0.55°C increased from 1.42% to 20%. The acidity was 13.5°0 (Oornic degree) with a mean of 1 7 .64°0 at the first day which was increased to 16.2°0 and 42.3°0 with a mean of 21.05° 0 after being preserved for one week. An inverse relationship was observed between acidity and F.P. which was significant as seen by the Student's t-test (p<0.05).