The method is applicable to products having acidities equal to or greater than 0.0008 % (m/m). The principle consists in the dilution of a test portion with carbon dioxide-free water, checking whether the test solution is alkaline or acid to phenolphthalein, and, if appropriate, determination of the acidity by titration with standard volumetric sodium hydroxide solution. The acidity is expressed as a percentage by mass of acetic acid. - International Standards ISO 1388/1 to 1388/12 cancel and replace ISO Recommendation R 1388-1970 of which they constitute a technical revision.