AbstractThe organic acid constituents of cider‐apple and perry‐pear juices and the microbiological changes which they undergo during fermentation have been investigated using methods based on ion‐exchange and paper chromatography. The main changes observed during fermentation were the conversion of malic acid to lactic acid and of quinic acid to dihydroshikimic acid, both of which were brought about by lactic acid bacteria. These bacteria also broke down citric acid, present in considerable amount in some perry‐pear