ISO 26323 |IDF 213:2009规定了通过连续测量pH值来测量乳酸菌酸化活性的方法。 该方法适用于存在这些特征微生物的乳制品发酵剂培养。 程序中规定了两种标准牛奶:干物质质量分数为9.5%的煮沸牛奶（B-牛奶9.5）；以及干物质质量分数为9.5%的蒸压牛奶（A-牛奶9.5）。B-牛奶9,5的热处理可能不会使存在的所有酶失活，这可能会影响某些培养物的活性。在这种情况下，用所有酶都已失活的A-milk 9,5测试培养物。

ISO 26323|IDF 213:2009 specifies a method for the measurement of the acidification activity of lactic acid bacteria by continuous measurement of pH. The method is applicable to dairy starter cultures where these characteristic microorganisms are present. Two types of standardized milk are specified in the procedure: boiled milk with 9,5 % mass fraction dry matter (B-milk 9,5); and autoclaved milk with 9,5 % mass fraction dry matter (A-milk 9,5). It is possible that heat treatment of B-milk 9,5 does not inactivate all enzymes that are present, which can affect the activity of some cultures. In that case, cultures are tested with A-milk 9,5 in which all enzymes have been inactivated.