Over the past couple of decades, some producers of olive oil have experimented with removing pits from a newly-harvested crop before pressing it into olive oil. But the results have been mixed and consequently, this practice is only followed by a handful of growers around the world. While there may be some advantages, especially in the area of producing a milder taste and ease on the machinery, clearly removing the pit before processing does not create a superior olive oil.
There are three issues that are discussed with this method: whether the process creates additional exposure to oxygen, thereby leading to early deterioration of some nutritive values; whether the taste profile differs when removing the pit prior to processing; and the economic impact of the process.
Ron Asquith of Ojai Olive Oil, a grower in California’s Central Coast, was the first to provide us with some anecdotal experience with pitting olives for olive oil. Asquith began his operation 11 years ago, using a system that depitted the olives before pressing. While depitting eliminated the crushing process, because it sufficiently shredded the olive, he came to prefer the robust flavour of olive oil created when crushing pits and fruit together. With no discernable chemical differences, it was enough to cause him to change methods five year ago and return to the classic approach.
To find out the latest information about the process of depitting and get a scientific point-of-view, we then went straight to Leandro Ravetti, our featured Personality Profile this month, to get his expert opinion. Ravetti’s report supports the conclusion that while depitting olives used for olive oil may certainly impact flavour profile, it does little to improve nutritive values.
“The practice (of depitting olives) is relatively new, of limited adoption within the industry and there are only a handful of comprehensive research works covering the topic. Independent research studies (Patumi et al, 2003) concludes that the technology of extracting oil from stoned olives, proposed by some oil machine companies and supported by some researchers, does not lead to a net qualitative advantage in the extra virgin olive oil obtained from stoned olives. This research is in line with my own experience where free fatty acid values, peroxide values and UV coefficients do not show statistical differences between oils processed from whole or pitted olives.
Regarding shelf life, some studies (Frega et al, 1998) would indicate a potential better shelf life of those oils produced from depitted olives when comparing oils from cultivars Frantoio and Moraiolo. This study attributed the greater stability to the hypothesis that during grinding and malaxation, the contact of oil of the pulp with the embryo present in the stone causes a series of enzymatic reactions, among which are the oxidative ones (LOX), that influence the shelf life of the product. Nonetheless, later research studies showed no difference between the LOX activity in whole and stoned olive paste, concluding that stoning makes no difference on the different oils shelf life.
The principal qualitative difference between regular extra-virgin olive oil and extra-virgin olive oil made from depitted fruit would be in the taste. The latter tends to be sweeter and more delicate while traditional extra-virgin olive oil is more aromatic and strongly flavoured.
Of equal importance, whether this difference is a positive or negative aspect for one or the other system largely depends on the type of fruit being processed (variety, environment and growing conditions). All studies agree that those three factors: variety, environment and growing conditions have significantly more influence on the final character of the oil than if the olives have been depitted or not before crushing.
An extremely important aspect to consider while comparing both technologies is related to extraction efficiencies. Some of the previously mentioned studies show that paste from depitted olives tends to yield 15 to 20% less oil than traditionally processed fruit. My personal experience and a number of personal communications with experienced millers would confirm those differences.
Summarizing, I believe that removing the pit before crushing does not improve the chemistry of the oil, but significantly decreases extraction efficiency. The grower/processor should then evaluate the slight organoleptic changes produced by the technique in a similar way than other processing changes are normally judged (e.g. by-passing the washer or not, changes in the crushing grid, time and temperature of malaxing, etc) and determine if those changes, under their specific growing and processing conditions, are appropriate to achieve the style of oil that they want and the premium price needed to compensate the lower oil yields.
We’d like to thank both Ron Asquith for his informal, in-the-field assessment of this topic and Leandro Ravetti for his comprehensive overview of the issue.