This study investigated the correlation between total polyphenol content and the stability (ie induction time by Rancimat) of oil samples according to di โ erent regions, cultivars, extraction technologies and ripening times of raw material. Results indicate a correlation of oil stability with total polyphenols, (r \ 0ร88), a chemical variable easy to determine. We have set up an oil quality index as a measure of desirability including legal parameters, especially the Council Olive Oil International score (COI Score), stability (phenol content) and process yield into account. The study of the e โ ects of olive ripening and storage prior to processing and olive paste mixing times and temperatures on the quality index using an experimental factorial design (24) were investigated. The process variables selected in the experimental factorial design were studied and the main e โ ects on desirability were identiรed. Based on this information, the extraction process was optimised for quality index in relation to fruit ripening and olive paste mixing time using a response contour to identify optimal experimental conditions. This innovative procedure shows that process conditions can be optimised as a function of evaluated according to scientiรc determinations. D tot , 1998 SCI.