How Is Olive Oil Made?

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Olives are picked and sorted, then crushed and milled into a paste. The paste is spread over bags and put into a hydraulic press, where the olive oil is extracted. The olive oil and vegetable water are separated by centrifuge, then the olive oil is bottled or canned.

Olives and the trees on which they grow have been revered as sacred since ancient times. Archaeological digs have found evidence of the existence of olive trees dating back to 3500 B.C. in Crete, one of Greece’s largest islands. The oil from the olives was actually used to cover their bodies from head to toe for religious purposes. In Hebrew culture, there is a law stating that one must not cut down an olive tree; this law is still followed today! Now that we understand some of the significance of the olive, let’s take a look at the raw materials needed to create olive oil.

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Raw Materials

(Photo Credit: Pixabay)

The primary ingredient is the oil extracted from the olives. The olive tree flowers bloom in late spring, and cross-pollination occurs through air movement. After the pollination, the flowers turn into olives. It takes approximately six months for the olives to contain their peak oil content. Thus, the olives are harvested from November to March. The harvesters observe the change in color of the olives to harvest effectively; they usually turn from green to dark blue or black, which serves as an indication of ripeness. The harvesting of olive batches usually occurs from the same tree, as this ensures that the olives of the same matured age are obtained.

Since ancient times, the process of harvesting olives has typically involved using long poles to knock the olives down. This is still practiced to this day. Originally, nets were used to catch the falling olives, but today, clean plastic sheets are used so that the process of harvesting the falling olives is smooth, clean and efficient.

The highest grade of virgin olive oil is usually 0.95L of extra virgin olive oil. To obtain this quantity of extra virgin olive oil, around 2000 olives are needed. The only extra ingredient added to virgin olive oil is water. The water helps in washing away the slighty bitter taste caused by the presence of oleuropein. Extra virgin olive oil does not contain more than 1% oleic acid. Pure olive oil is obtained from the second pressing of the same olives.

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Manufacturing Process

collecting and grading
(Image Credit: Flickr)

The first stage in the manufacturing process consists of collecting and grading the olives. After the collection of the ripe olives, they are inspected by trained harvesters who pick out the unfit ones. The olives are then divided into certain classes based on their plumpness, state of ripeness and quality. After this separation is over, the olives are taken to a press. The olives are stored in the press for a certain length of time, which can range from a few hours to a few weeks. The storage time is well planned, so that it’s not long enough for the olives to ferment, but just long enough for the olives to become tender enough to extract the oil from them. The next stage involves washing and milling the olives. They are then rinsed in cold water and passed along a conveyor belt. This conveyor belt consists of a roller and hammers, and this machine is known as the olive crusher. The crusher breaks down the cell and de-stones the olives. After the milling of the olives, they are pushed into vats containing slow-moving blades that change the olives into a homogeneous paste.

The homogenous paste is then loaded onto a hydraulic press, which is where the oil is obtained. This is the stage where cold pressing occurs. The olive paste is evenly spread over disks covered with synthetic bags. Each bag or disk is covered with 4-6kgs of paste. There are between 25-50 bags placed between the plates of the hydraulic press. The piston pushes up the stack and the oils seep through the bag into the attached tubing, which collects the oil. The solid residue material remains within the bag. The term cold pressing refers to the fact that the oil is extracted without any heating, which guarantees the purity of the oil. The collected oil is reddish and contains olive oil, as well as a certain amount of vegetable water. The next step involves separating the vegetable water from the olive oil.

In the past, the oil and water mixture was stored in vats until the oil rose to the top and could be skimmed off. Some fermentation was inevitable, which affected the taste and smell of the olive oil. Today, the separation is accomplished far more swiftly by pumping the mixture into a centrifuge. The centrifuge is comprised of a rotating drum and an auger that is spun on the same axis at great speed. Because the oil and vegetable water are of differing densities, the centrifuge forces them apart and into separate receptacles. The oil is stored in underground vats until it is ready to be shipped. The oil is then canned or bottled on an assembly line. Cans or dark-tinted bottles will keep the deep-green color of the olive oil intact. Oil placed in clear glass bottles will fade to a yellowish-green, but the flavor will not not affected.

In many cases, olive oil distributors purchase the olive oil from the producers and rebottle it. Packaging has become more ornate as the popularity of olive oil has grown. It’s not unusual to purchase olive oil in unusually shaped bottles topped with netting or rope. Some packagers even hire professional artists to design their labels!

With all of this in mind, next time you walk down the aisle in the supermarket and reach for your next bottle of healthy olive oil, you’ll know exactly what it took to get there!

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References (click to expand)
  1. Olive oil - Wikipedia. Wikipedia
  2. How Olive Oil is Made - Food and Recipes | HowStuffWorks. HowStuffWorks
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About the Author

Venkatesh is an Electrical and Electronics Engineer from SRM Institute of Science and Technology, India. He is deeply fascinated by Robotics and Artificial Intelligence. He is also a chess aficionado, He likes studying chess classics from the 1800 and 1900’s. He enjoys writing about science and technology as he finds the intricacies which come with each topic fascinating.