Olive Oil Production and Processing Techniques

The olive tree, belonging to the Oleaceae family, has been cultivated along the Mediterranean coast for over 4,000 years. Alongside camellia oil, palm oil, and coconut oil, it is considered one of the four major woody oil crops. Olive oil is extracted from the fresh fruit of the olive tree (excluding oils obtained through solvent extraction or transesterification processes, and without mixing with other types of oils). It is rich in balanced fatty acids, antioxidant phenolic compounds, vitamins, and other nutrients. These attributes help reduce the risk of cardiovascular and coronary heart disease, lower LDL cholesterol levels, and may aid in preventing cancers such as breast and colon cancer, as well as offering antibacterial and antiviral benefits. Due to its long history and rich nutrition, olive oil is known as "liquid gold" and the "queen of vegetable oils," prized by consumers for its unique flavor.

Olive oil can be categorized into three main types based on processing methods: virgin olive oil, refined olive oil, and blended olive oil. Virgin olive oil is further divided into extra virgin olive oil, fine virgin olive oil, and ordinary virgin olive oil. Among these, extra virgin olive oil is the highest grade and can be consumed directly. The variety of olive, its ripeness, and the processing techniques used all significantly affect the quality of the olive oil. Today, I’ll walk you through some key points regarding olive oil production processes.

Olive Oil Production Process

Key Olive Oil Production Techniques

Harvesting and Selection of Fresh FruitThe timing of olive fruit harvesting should be determined based on the variety and the desired characteristics of the olive oil. Early harvesting results in a lower oil yield but a higher polyphenol content. In contrast, later harvesting increases the yield but lowers the polyphenol levels. Additionally, green olives contain less oil but are higher in polyphenols, while black olives have a higher oil content but lower antioxidant levels. To ensure both oil quality and yield, the ideal ratio of green to black olives is 75:25.

The olives are harvested manually or using mechanical equipment. Olive oil pressed from fruit that has fallen to the ground will have a significantly higher acidity, so care should be taken to avoid direct contact with the ground during harvesting. Damaged, shriveled, rotting, or diseased fruits should be removed, and the harvested fruit should not contain soil, branches, leaves, or other debris.

Transportation and Storage

Freshly harvested olives should be placed in small baskets, then stacked and transported to the processing facility. They should be spread out in a ventilated storage area to avoid excessive pressure, heat, or bruising, which can lead to oxidation and fermentation. In practice, olives are often stored in large burlap sacks, so the storage time should not exceed 1–2 days.

Leaf Removal and Cleaning

Belt conveyors and air separators are used to remove leaves from the olives. Leaves contain chlorophyll, which can oxidize under high temperatures during crushing and blending, negatively affecting the quality of the oil. The fruit should be evenly distributed on the conveyor during leaf removal to ensure efficiency. Additionally, the airflow in the fans should be unobstructed, and any debris on the conveyor should be regularly cleared to enhance leaf removal.

During the washing process, the water should be replaced every 10–12 hours, and stones or other impurities should be removed from the filter screens.

Crushing

After pre-treatment, the olives are crushed to break the plant cells and release the oil from the fruit’s flesh. There are two crushing methods: stone milling and mechanical crushing. Mechanical crushing significantly increases the total phenol content in the olive oil compared to stone milling, as it allows more complete exposure to different cell tissues in the olive, thereby increasing the phenolic compounds. Water can be added during crushing, depending on the fruit’s ripeness, to aid in crushing, cooling, and later blending.

Blending

Blending is a critical step in the processing technique, directly affecting both oil yield and quality. The blending time is determined by how well the oil droplets coagulate in the paste. The optimal blending time is around 30 minutes. A shorter time reduces oil yield, while a longer time accelerates oxidation in the paste, lowering the quality of the oil. The temperature during blending should be maintained between 27°C and 30°C, and the machine’s rotation speed should be between 30–50 rpm.

Centrifugal Separation

The centrifugal separation system can be either three-phase or two-phase. The three-phase system separates the crushed paste into pomace, wastewater, and oil, requiring a large amount of water during separation and producing more wastewater. The two-phase system, which doesn’t require water, separates the paste into pomace and oil, though the pomace retains some water and requires further separation.Currently, most producers use the three-phase centrifugal system, with a smaller number using the two-phase system. The three-phase system requires the addition of 40–50% water, with the pomace accounting for about 45% of the total, and a residual oil content of 4–6%, while the oil yield is around 25%. The two-phase system does not require water, the pomace makes up about 75%, with a moisture content of 60–65%, and the oil yield is also around 25%.

Storage

After a short period of natural settling in conical tanks, virgin olive oil is filtered and transferred to stainless steel storage tanks, kept away from light and heat, and filled with nitrogen if necessary. Small amounts of water and sediment are periodically drained from the tanks. If the oil remains cloudy, it can be mixed with diatomaceous earth and filtered through a plate frame. Samples of the olive oil are regularly tested for quality control.

In the production process, each step—including harvesting, transportation, storage, leaf removal, washing, crushing, blending, centrifugal separation, and storage—affects the quality of the olive oil. Therefore, it is essential to control the parameters at each stage and innovate in key processes to ensure the production of high-quality olive oil.

References

1. Qi Haihong. Discussion on Olive Oil Processing Techniques and Characteristics [J]. Food Safety Guide, 2018(6):141-143.
2. Guan Lei, Qian Yu. Discussion on Olive Oil Processing Techniques and Characteristics [J]. Construction Engineering Technology and Design, 2020(22):123.
3. Zhao Haiyun, Wang Xuwu, Li Jinhua, et al. Extra Virgin Olive Oil Processing Technology [J]. China Food Industry, 2010(6):49-50.
4. Li Yuyin, Deng Congjing, Zhang Quanzhou. Preliminary Exploration of High-Quality Olive Oil Processing Techniques [J]. Forest Products Industry, 2014, 41(6):37-39.
5. Sun Shumin, Xie Yanli, Zhao Wenhong, et al. Research Progress on Characteristic Chemical Components and Flavor Substances of Olive Oil [J]. Journal of Henan University of Technology (Natural Science Edition), 2015, 36(5):113-119.