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Note: This article was AI-translated from Arabic and is currently under manual review. The author is not responsible for any translation errors. Please refer to the original Arabic text for the most accurate and authoritative information.
Olive Oil Quality from Tree to Table | Episode One
How do mistakes in irrigation, fertilization, orchard care and harvesting affect olive oil quality before the fruit reaches the mill?
We can lose part of an olive oil's quality before the first fruit even enters the mill. A tree that looks strong, large glossy fruit and an abundant crop do not, on their own, reveal whether field practices have set the stage for an outstanding oil, or have hidden problems that will surface later in its flavour, stability and value.
Ahead of the olive harvest season in Egypt and the Arab world, it is worth reviewing decisions that seem routine: When do we irrigate? What do we fertilize with? How do we care for the tree and protect its fruit? When do we harvest? These decisions determine the quality potential the farm hands over to the mill. Not every difference in composition between oils means something went wrong; variety, environment and ripeness are natural factors that should be understood during evaluation.
Larger fruit may look like success, yet on its own it reflects neither the amount of oil nor how easily it can be extracted. Studies show that the effect of irrigation on phenols and oil characteristics varies with variety, fruit growth stage and the severity of water deficit; so it is wrong to generalize that more water improves quality, or that water-stressing the trees always raises it. [1, 2]
The hidden mistake is irrigating every block on the same schedule despite differences in soil, crop load and tree condition. It is better to monitor soil moisture, the tree's needs and the uniformity of the drippers, while checking water quality and drainage. Nor should a fixed date for stopping irrigation before harvest be adopted on every farm; the decision should be set locally, in cooperation between the agronomist and the mill. [3]
Excess fertilizer may produce vegetative growth that pleases the eye while some oil characteristics decline. In a long-term field trial on the Barnea olive variety, a higher nitrogen supply was associated with higher free fatty acids and lower phenols, while the peroxide value was not affected in the same way. This shows why a single observation does not reveal all the effects of fertilization. [4]
In practice, this means building a balanced programme on leaf analysis, supported by soil and water analysis, and taking crop load and the records of previous years into account. A fertilization recipe copied from another farm, or extra nitrogen "just in case", may add cost without improving the oil. Doses from a research trial should not be generalized to different varieties and regions. [4]
Crowded branches can block light and weaken ventilation and the penetration of pest-control treatments into the canopy, making diseases and pests harder to manage. On the other hand, heavy pruning is not a routine cure for this problem. What is needed is balanced pruning that suits the tree's age and the harvesting method, removing infected parts and managing pruning residues, while cleaning pruning tools to limit the spread of infection. Healthy fruit begins with the environment it grows in. [3]
Infestation holes may look small, but the damage extends into the fruit tissue and can open the way to microbial changes that affect the oil. Research on the olive fruit fly has shown changes in aroma compounds and phenols that differ by variety and infestation status. That is why growers should not wait for visible rot before they start monitoring. [5]
Prevention rests on regular monitoring, integrated pest management and decisions taken together with a specialist. When a pesticide is used, its registration for the crop, its label instructions and its pre-harvest interval must be respected, and the treatment documented. Residue safety is a separate issue from a good aroma or low acidity, and the requirements of the target market must be taken into account. [3]
Waiting until all the fruit turns black, or sticking to last year's date, can miss the best moment. Oil accumulation and fruit ripening do not progress at the same pace in all varieties and environments; harvesting too early may reduce yield, while a delay may bring a decline in some attributes or more fruit drop and infestation risk. [6]
The date is set by following representative samples from each block and variety, checking ripeness, fruit health and oil and moisture content, and making use of a trial extraction and tasting of the oil. A common mistake is to read the higher oil percentage in shrivelled fruit as entirely new oil formation; the figure may rise on a fresh-weight basis simply because of water loss. That is why it also helps to track oil content on a dry-matter basis. [6, 7]
Cuts and bruises from rough harvesting, falls and pressure may not catch the worker's attention, but they weaken tissue integrity and make the fruit more prone to deterioration before milling. This does not mean rejecting mechanical harvesting; the result depends on how suitable the machine is and how it is adjusted, as well as on variety, ripeness and processing speed. [8]
Fruit that fell to the ground long ago must be kept separate from sound fruit picked from the tree, clean nets should be used during harvest, and contact of the crop with soil, leaves and twigs should be kept to a minimum. Washing the fruit later does not restore damaged tissue to its original state. [9]
Harvesting may be done carefully, only for the mistake to begin with piling the fruit in sacks or hot heaps while waiting for a full transport load. Harvested fruit keeps respiring, and fermentation and spoilage can accelerate with heat, wounds and poor ventilation. A study covering 228 batches showed that longer storage of fruit before processing was accompanied by a loss of positive sensory attributes and a decline in quality indicators. [10]
The fruit should therefore be placed in clean, ventilated, food-grade crates, without pressing or excessive stacking, and kept in the shade while being prepared for delivery. Harvesting should be coordinated in advance with the mill's capacity, aiming to process the fruit as soon as possible, preferably on the day of harvest. This is an operational priority, not a guarantee that all fruit can withstand waiting until the end of the day. [9, 10]
Before we ask the mill about its extraction yield, let us ask the farm about its irrigation and fertilization records, the health of the fruit, and why the harvest day and method were chosen. Protecting quality starts with documented decisions, and with a sound crop that reaches the mill's door quickly.
This is where the responsibility of the next stage begins: how do we preserve the potential the fruit carries during crushing, malaxation and separation? That is the subject of the second episode of the series "Olive Oil Quality from Tree to Table" on Zyot W Dhon.
[1] Summer deficit-irrigation strategies in a hedgerow olive cv. Arbequina orchard: effect on oil quality. Journal of Agricultural and Food Chemistry, 2013, Open original source
[2] Deficit irrigation during the oil synthesis period affects olive oil quality in high-density orchards (cv. Arbequina), Open original source
[3] IOBC-WPRS — Integrated Production Guidelines for Olives. Chapters on irrigation, nutrition, pruning and crop protection, Open original source
[4] Zipori et al. Effect of macronutrient fertilization on olive oil composition and quality under irrigated, intensive cultivation management. Journal of the Science of Food and Agriculture, 2023, Open original source
[5] Notario et al. The Infestation of Olive Fruits by Bactrocera oleae (Rossi) Modifies the Expression of Key Genes in the Biosynthesis of Volatile and Phenolic Compounds and Alters the Composition of Virgin Olive Oil. Molecules, 2022, 27(5), 1650, Open original source
[6] International Olive Council — Production techniques in olive growing, 2007, chapter on harvesting and its mechanization, Open original source
[7] Olive paste oil content on a dry weight basis (OPDW): an indicator for optimal harvesting time in modern olive orchards. Grasas y Aceites, Open original source
[8] Does the Harvest Type Affect Olive Health? Influence of the Harvesting System and Storage Time on the Chemical, Volatile and Sensory Qualities of Extra Virgin Olive Oils, Open original source
[9] University of California, Davis — Olive Oil Quality, Open original source
[10] Rotondi et al. Effect of Duration of Olive Storage on Chemical and Sensory Quality of Extra Virgin Olive Oils. Foods, 2021, 10(10), 2296, Open original source
