Prasaplai is a Thai traditional preparation composed of twelve ingredients; during storage three newly emerging compounds were detected by HPLC. Their structures were established as the new (E)-4-(3,4-dimethoxyphenyl)but-3-en-1-yl linoleate, (E)-4-(3,4-dimethoxyphenyl)but-3-en-1-yl oleate and the known (E)-4-(3,4-dimethoxyphenyl)but-3-en-1-yl palmitate on the basis of spectral data and chemical evidence. The artificial esters were already observable after one day of storage of the freshly prepared dry mixture, and steadily increased during a storage period of 30 days and more. A systematic search indicated that the three esters arose from the interaction of compounds contained in the rhizomes of Zingiber cassumunar and the seeds of Nigella sativa.