It’s always exciting to bring in your first harvest. The orchard produced a healthy crop and you have high expectations of how much oil you’ll get at the mill. But, veterans know that calculating oil yield from acreage is not a simple science. It involves many factors and oftentimes even seasoned producers can enthusiastically overestimate the result.
Even before the harvest begins, it’s important to consider four key factors in determining yield:
- Orchard composition is the first point of information to determine your annual yield. Start by factoring in density, or how many trees you have per acre, and then add consideration for the age of the trees, the weather, the annual alternating cycle that is natural to fruit-bearing trees (heavy crop/light crop), and the type of orchard management you employ (water schedule, fertilizers, pest control, pruning).
- The type of olive variety you grow will have much to do with how high the yield will be and it can vary greatly. Certain varietals contain much heavier concentrations of oil than others. Another key to understanding yield is that fruit size does not determine oil content. Despite its size, the very large Sevillano olive may yield as little as 8 G/T (gallons/ton) because its own oil/pulp ratio is much smaller than some olives half its size. On the other hand, some ripe Arbequina fruit can yield as much as 55 G/T. On average, Italian varietals might yield between 40 to 45G/T, but the popular and common Mission and Manzanillo olives are much less consistent.
- The time of harvest will affect the concentration of oil to pulp in the fruit. The later you harvest in the season, the riper the fruit and the higher the oil content. Ripeness of fruit, though, greatly affects the flavor profile, health benefits and shelf life. A grassy, sharp taste of early harvest oils is an indication of higher polyphenol content, so you may not want to trade off an early-harvest spicy style for a late-harvest buttery style just to get a higher yield.
- The amount of fruit hydration that exists at the time of harvest can create a false impression of fruit weight. The best yield is the result of the proper balance between hydration and desiccation. Importantly, most mills charge by fruit tonnage, not oil yield. So, there is no value in bringing fruit to the mill that is heavily saturated with water weight. You are paying for water that will be removed in the milling process. It is typically recommended that you closely monitor your seasonal rain patterns or stop your watering schedule altogether within two weeks of harvest to control this factor. Some fruit, and in particular Mission, can turn into little water balloons if overwatered. This excess water can form an emulsion with the oil, which makes it very difficult to extract the oil and results in a lower yield. Talc helps a lot with this problem.
It’s great to be excited about your harvest, but also smart to set realistic expectations of the outcome. Being conservative in your planning always provides for the best possible result: a strong yield in a good year. For further, detailed information about oil yield, an excellent article from UC Davis by one of the members of our Olive Expert panel, Paul Vossen can shed even more light on this subject.