The acidity of consumer oils is a confusing term. On the one hand, the labelling of the oil bottles does not clarify its meaning and, on the other hand, the causes of the acidity of the oil and how it affects virgin and refined olive oils are generally unknown.
The oil is found in the olive in the form of triglycerides. This means that three fatty acids are linked to form a molecule known as glycerol, which is the most stable molecule that we can find in oil.
Acidity occurs when, due to oxidation processes, glycerol molecules break down into the three free fatty acids that compose them. Therefore, we will find intact original molecules (triglycerides) and fatty acids in the same space, which are responsible for the acidity of the oil.
In order to obtain a high quality extra virgin olive oil with less quantity of fatty acids we need to look after the harvesting process for the olives, as well as the production process in which we get the paste and, then, the oil.
- Processes that generate acidity.
- Loss of the skin that covers the fruit and the prolonged stay of the olive on the tree, which can be affected by hail, or by the action of birds or pests.
- Prolonged exposure of the olive meat during harvesting by blows, or towing.
- Crushing of the olive during storage prior to oil extraction.
- Storing the paste resulting from milling for an excessive time.
- Finally, incorrect oil maintenance in the tanks, either due to leaks, or air exposure that may remain in the upper part of the tank.
When the final acidity of the oil is measured, it’s when we know the value of the free oleic fatty acids (that is, not grouped in triglycerides) with respect to the total weight of the oil.
Extra virgin olive oil must have an acidity below or equal to 0.8 degrees. In the case of virgin olive oil, it must be below 2 degrees. If the acidity exceeds 2 degrees, the oil will be classified as refined oil.
As we said, acidity is an indication of how the olive has been treated during its life on the tree and during its collection, as well as how the oil extraction process has been carried out resulting in its quality. However, acidity is only a factor applicable to extra virgin olive oil.
When it comes to refined oils, acidity doesn’t correspond to these same actions, since it has been distorted by the different chemical processes to which it has been subjected. Refined oil is tasteless and colourless, so when mixed with virgin or extra virgin oils, the resulting blend will have low acidity but also poor flavour and low quality.
Due to this, and to the confusion generated by the legislation, if the oil producer wishes to publish the acidity of his oil, it must be accompanied by other parameters such as wax content, peroxides and ultraviolet absorbances.
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Acidity and flavour
Acidity is often confused with the oil bitterness or sweetness. When we talk about this acidity, we don’t mean it’s an organoleptic feature of the oil (which is detectable by the senses), but it’s a quality evaluated in laboratories.
The acidity of the oil doesn’t have to do with its flavour, but with its quality and with the treatment given to the raw material and the oil during its production.
Acidity is also an indicator of how many beneficial qualities are left in the oil, since these also degrade by oxidation. So, the lower the acidity is, the lower the oxidation and the higher the oil benefits.
Make sure you buy extra virgin olive oil, which is the only one that guarantees that the acidity has not been modified by chemical processes.