The present invention aims to provide extracts available for use in acidic beverage production and containing 2,5-piperazinedione,3,6-bis(phenylmethyl)-,(3S,6S)-, which is a useful substance with an improving effect on learning motivation. When an acid treatment step is included in the production of extracts containing 2,5-piperazinedione,3,6-bis(phenylmethyl)-,(3S,6S)-, it is possible to obtain acidic extracts which cause no sedimentation even when added to beverages. The extracts of the present invention can be added to beverages and so on without impairing the taste inherent to foods and beverages, and can be used for production of acidic beverages preferred by most consumers.本發明之課題在於提供一種含有具有改善學習意願作用的有用物質之2,5-哌嗪二酮,3,6-雙(苯基甲基)-,(3S,6S)-，且可使用於酸性飲料之製造的萃取精華液等。解決上述課題之方法在於，在含2,5-哌嗪二酮,3,6-雙(苯基甲基)-,(3S,6S)-之萃取精華液的製造中，藉由包含酸處理步驟而可獲得即使在添加到飲料的情況下，也不產生沈澱之酸性萃取精華液。本發明之萃取精華液係不損及飲食物本來的呈味而可添加於飲料等，在市場上，可用於嗜好之酸性飲料的製造。
