This International Standard describes a Potentiometric method for determining the pH of the aqueous phase of all types of food preserves. It is particularly intended to be used to check the biological stability of food preserves. This International Standard is applicable to the following four classes of product. Class 1: homogeneous products with a liquid or thick texture, or products exhibiting a large liquid or thick phase which imparts a presumed uniformity of pH to the product. Class 2: homogeneous pastes or heterogeneous products for which homogenization is necessary. Class 3: heterogeneous products with large solid components. Class 4: products whose liquid phase mainly consists of oil or a water/oil emulsion. Measurements may be made at 20 °C or at 25 °C, the temperature chosen being stated in the test report