Optimisation of olive paste expression: a study of variables affecting expression yield

The influence of some operating variables on olive paste expression rate and yield has been investigated using a laboratory expression apparatus. Results show that compaction rate and cake thickness have a primary importance in determining the extraction rate. Temperature has a limited effect. A pressure increase beyond 50.7 × 105 Pa is also of little benefit. Data on product variables show that the rigid solids play an important role and that the natural pit fragments content in olives is well below the optimal value. An extraction yield as high as 95% was obtained by adding pit fragments up to 40% by volume of olive paste. This value is noteworthy because it was obtained during the expression phase carried out at constant flow rate, while the expression phase carried out at constant pressure was not taken into account. Based on these results, an optimisation experimental design will be presented and validated in a following work.