The olive (Olea europaea) is deeply intertwined with the history of the Mediterranean basin, where its cultivation has shaped landscapes and economies for millennia, providing both oil and table fruit. This ancient crop requires specialized care and processing to transition the bitter fruit from the branch to the global market.
Geographical Requirements for Olive Trees
The olive tree thrives in a specific set of climatic conditions. Its successful cultivation is strictly limited by temperature requirements, particularly the need for winter chill. The tree requires a period of low, non-freezing temperatures, known as vernalization, to initiate flower bud differentiation.
Cultivars vary in their needs, but many require hundreds of hours below $7^{\circ}\text{C}$ for proper development. A period of long, hot, and dry summers is then necessary for the fruit to mature properly. The tree’s resilience allows it to flourish in poor, rocky, and well-drained soils, often with a slightly alkaline pH, making it highly adaptable to marginal agricultural lands.
Agricultural Management of Olive Groves
Successful olive production requires years of dedicated cultivation before trees reach their full productive potential. Pruning is a fundamental, annual practice performed to manage the canopy structure, ensure maximum sunlight penetration, and promote good air circulation to manage disease. This structural management influences the tree’s natural tendency toward biennial bearing, where a year of heavy production is followed by a year of low yield.
In modern high-density and super-high-density groves, specialized irrigation strategies are employed to stabilize production and conserve water. A common method is Regulated Deficit Irrigation (RDI), which strategically restricts water supply during less sensitive growth phases, such as the pit-hardening stage in mid-summer. This controlled stress can save significant amounts of water while often enhancing the concentration of desirable flavor compounds in the oil. Trees must also be protected from pests like the olive fruit fly, whose larvae bore into the fruit, and diseases such as Verticillium wilt, a serious fungal threat to the tree’s vascular system.
Methods of Harvesting the Fruit
The harvesting method depends heavily on the fruit’s final destination, either as table olives or for oil extraction. Table olives must remain unblemished for presentation and are often harvested using labor-intensive, gentle methods like hand-picking. This careful manual approach minimizes bruising, which can trigger oxidation and fermentation, rapidly degrading the fruit’s quality.
Conversely, the majority of oil olives are harvested using mechanical methods for efficiency and speed. Large-scale groves often employ trunk shakers, which grip the tree’s trunk and vibrate it until the olives fall onto nets laid beneath the canopy. In super-high-density orchards, over-the-row harvesters strip the fruit from the hedgerow-trained trees. While faster and more economical, mechanical harvesting can cause more physical damage to the fruit, necessitating rapid transport to the mill to prevent degradation and preserve oil quality.
Processing Olives into Commercial Products
Olives are processed immediately after harvest into two main commercial products: olive oil or cured table olives. High-quality olive oil production begins with washing the fruit to remove debris and leaves, followed by crushing the entire olive, including the pit, into a paste. The resulting paste then undergoes malaxation, a slow churning process that allows microscopic oil droplets to coalesce into larger, more easily separable drops.
The oil is separated from the paste via centrifugation, where the difference in density forces the oil, water, and solid matter apart. To earn the designation of Extra Virgin Olive Oil (EVOO), the product must be extracted using purely mechanical means, without excessive heat (cold-pressed), and possess a low free acidity level. Table olives cannot be eaten fresh due to the presence of a phenolic compound that imparts a bitter taste. This bitterness is removed through curing, which can involve prolonged soaking in a salt brine for fermentation, a quick treatment with an alkaline lye solution, or dry-salt curing, which draws out moisture and bitterness.