テトラ乳清比重法による牛乳の加水試験の検討

The Tetra-serum hydrometric method as the official routine test for detecting added water in milk was evaluated with special reference to its accuracy and detailed procedure. In experiments with raw milk samples collected in the southern region of Okayama prefecture, it has been shown that the faultiness of turbid serum occurred frequently in the case of the official method is due to an insufficient concentration of acetic acid for preparing milk serum. This fault was improved not by the technical modification for separating milk serum, but by the use of 35% acetic acid instead of 20% in the official method. From 41 samples of normal milk serum prepared by the modified method, the average value and standard deviation of the specific gravity were calculated. The value is 1.0304 ±0.00132. Regression equation of the specific gravity of milk serum on added water ratio was obtained from the experiment of adding water to authenticated milk samples. It was concluded that milk serum samples having specific gravity not over 1.0260 may possibly contain more than 10 per cent of added water.