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One of the most important questions olive growers face is determining the right time to harvest their olives. To help growers make this decision, the Institute for Oliveculture at the Science and Research Centre Koper (ZRS Koper) has published a new technical brochure entitled When Is the Right Time to Harvest Olives?. The brochure provides clear and practical explanations of olive ripening processes and the factors that influence the quantity and quality of the oil produced.
The decision on when to harvest depends on more than just the colour or appearance of the fruit. As experts from the Institute for Oliveculture at ZRS Koper emphasise, harvest timing always involves a trade-off between quantity and quality. Earlier harvesting generally results in higher levels of phenolic compounds and other antioxidants, as well as greater oxidative stability of the oil. Later harvesting, on the other hand, usually allows for a higher oil yield during processing but may result in lower levels of phenolic compounds and reduced oil stability.
The brochure explains how oil is formed and accumulates within olive fruits, the dynamics of this process in Slovenian Istria, and how oil content is influenced by olive variety, weather conditions, water availability, pests, tree crop load and fruit maturity. Particular attention is also given to the distinction between the actual oil content of olive fruits and the oil yield obtained at the mill, which do not necessarily correspond.
Dr Maja Podgornik, Head of the Institute for Oliveculture at ZRS Koper, comments on this year’s olive harvest:
“Due to high temperatures and severe water shortages, this year’s harvest will particularly reflect the conditions in individual olive groves. On shallow soils and in exposed locations, drought and heat stress have been more pronounced. We can therefore expect oils with slightly higher levels of phenolic compounds and more pronounced bitterness and pungency, although olive variety and processing methods also play an important role.
An important advantage of this season is the good phytosanitary condition of the fruit. The olive fruit fly has not caused significant damage, while weather conditions have not been favourable for the development of fungal diseases.
Initial results indicate that the 2026 harvest has good quality potential. However, further chemical and sensory analyses of oils from different locations will be required to provide a more reliable assessment. It will also be essential to preserve the quality potential of healthy olives through appropriately adapted processing methods at the olive mill.”
At the Institute for Oliveculture at ZRS Koper, olive growers can use the FT-NIR method to determine the oil content, water content and oil content on a dry matter basis in their olives. The results can provide valuable support for monitoring fruit ripening and selecting the most appropriate harvesting time.
The brochure was prepared as part of the Public Service for Oliveculture, funded by the Ministry of Agriculture of the Republic of Slovenia, and is available at the following link: