The principle of the method specified is preparing the test sample according to the class to which the product to be examined belongs, and measuring the potential difference between a glass electrode and a reference electrode immersed in the test sample. Applies to four classes of product: 1. homogeneous products with a liquid or thick texture, or products exhibiting a large liquid or thick phase; 2. homogeneous pastes or heterogeneous products for which homogenization is necessary; 3. heterogeneous products with large solid components; 4. products whose liquid phase mainly consists of oil or a water/oil emulsion.