The method is applicable to products having esters contents in the range 0.005 % (m/m) to 0.15 % (m/m). The principle consists in the saponification of esters present in a test portion by boiling with excess standard volumetric sodium hydroxide solution; determination of the residual sodium hydroxide, and hence the amount used for saponification, by titration with standard volumetric hydrochloric acid solution in the presence of phenolphthalein as indicator. - International Standards ISO 1388/1 to ISO 1377/12 cancel and replace ISO Recommendation R 1388-1970 of which they constitute a technical revision.