This International Standard specifies a method to evaluate the contents of free alcohols and total alcohols in essential oils by determination of ester values before and after acetylation by acetic anhydride in the presence of sodium acetate. The method is not applicable to essential oils containing appreciable quantities of tertiary alcohols (for example linalol and terpineols), which would not be completely acetylated. NOTE: For these essential oils the method given in ISO 3794 should be used. The method is not applicable to essential oils containing appreciable quantities of phenols, lactones, aldehydes or enolysable ketones, which would be acetylated in addition to free alcohols.