HOW OLIVE OIL IS MADE

From branch to bottle, discover the fascinating process of extracting this delicious and nutritious liquid gold.

Whether added to the pan before cooking, or enjoyed straight out of the bottle with some fresh bread, olive oil is a tasty and versatile staple in kitchens all over the world. The majority is produced in the Mediterranean, the olive tree’s native home, and the process begins with picking the fruit.

At least 4.5 kilograms of olives are needed to produce one litre of oil, and they are at their prime for only a few weeks a year, so picking needs to be done quickly. However, as olives are a soft fruit, they must also be treated with care, as any bruising can cause the oils to degrade. Large-scale farms use tree-shaking devices toencourage the ripe olives to drop, and then catch them in nets before they hit the ground.

Once they are at the processing plant, the olives pass through several diferent machines to extract the oil. Here, speed is also of the essence, as once the olives have been crushed, exposure to air reduces the oil’s quality. Some plants can process three tons of olives in just one hour. However, during the malaxing (mixing) stage, a longer mix extracts more oil with a more developed lavour, so many modern systems use closed mixing chambers full of a harmless gas, such as nitrogen, to prevent oxidation during a longer mix. The amount of oil produced can also be increased by adding heat or more water during mixing, but this also reduces the product’s quality.

To be classed as virgin or extra virgin, the oil must be kept below 27 degrees Celsius during processing to ensure that it is ‘cold pressed’. Once bottled, it should be stored (for no longer than two years) in a cool, dark cupboard to preserve its lavour and healthy properties.

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What is Extra Virgin Olive Oil?

The word ‘virgin’ in the name of some olive oils refers to the way in which they were processed. They can only be given this title if the oil was extracted through mechanical means such as pressing or crushing, and not refined with chemicals or high heat. The difference between virgin and extra virgin olive oil comes down to the olives. Virgin olive oil is made with slightly riper olives than extra virgin, giving it a paler colour and a slightly higher acidity. Extra virgin olive oil is usually a deeper yellow or green colour and must contain no more than 0.8 per cent acidity, giving it a superior taste.

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The History of  Olive Oil Production

People have been extracting the oil from olives for over 5,000 years, and unsurprisingly the method has changed quite a lot during that time.

In the past, the olives were crushed into a paste using large circular stones of granite that were turned by donkeys. The paste was then separated from the oil and water using a method called pressing. The paste was spread onto discs of hemp or coconut fibre, which were then stacked and placed in a press to squeeze out the liquid. The oil and water could then be separated quite easily as the two do not mix. Today, some mills still practice the pressing method, but their discs are made of synthetic fibres and a more powerful hydraulic press is used.

In "How It Works" UK, issue 99, 2017,excerpts pp. 34-35. Adapted and illustated to be posted by Leopoldo Costa