The first thing that comes into your mind when thinking of the term "acidity" is probably, as in my case, burning, stinging, somehow sparkly sensation. Which is pretty much what acidity also refers to: burn sensations in the stomach, in the chest, in the throat, on the skin.
Not in olive oil
Speaking about olive oil acidity without taking a look at the chemical composition will not bring you further. There's a lots of resources online that will give you the definition of acidity. Few to none. of them give a clear understanding of :
what is triggering it
what is the result of it
why is acidity bad, not only from a quality point of view, but from aa nutritional as well
Since we find it hard to put this so important aspect in just a couple of words, we'll try giving it a "not so technical" explanation. Be aware though, you're onto a high-school chemistry lesson refresh !
Olive oil acidity - The first chemical quality standard
Definition of olive oil acidity
Olive oil acidity is a proportion of the free fatty acids measured in relation to the number of total oleic fatty acids (which is at 65 - 85 % of total fatty acids the predominating fatty acid in olive oil)
Why is this important: free acids are prone to oxidation and other exogenous effects, which on long term may have an effect on the flavors of olive oil as well, since long exposure to oxidation can eventually turn into rancidity. This is one of the reasons there is an official classification of virgin olive oil, which (among others) take into account the acidity level
Categorization of olive oils based on acidity
Extra virgin olive oil: no more than 0.8 %
Virgin olive oil: between 0.8 and 2 %
Lampante oil (not recommended for consuming without being filtered first): > 2 %
In other words, the lower the acidity, the better the olive oil. If processed correctly, paying attention to harvesting, transportation, storage, milling and taking into account the time dimension (oxidation is directly proportional with time), the final acidity of any olive oil, regardless of cultivar, climate and soil will be very low.
So, although an acidity of maximum 0.8 % is set as limit for an extra virgin olive oil, a very high quality olive oil should actually not exceed 0.3 % acidity
It is very important to understand that acidity is a characteristic that cannot be measured using organoleptic analysis (taste, smell) This is very often a misunderstanding, since a lot of people (actually the vast majority) confuse pungency with acidity (actually pungency is a key indicator of a high phenolic content, and is a sign for excellent olive oil quality)
Olive oil acidity is a chemical number and cannot be tasted. It is the proportion of free fatty acids in the oleic acid.
The lower the acidity, the better the olive oil
Extra virgin olive oils have a maximum acidity of 0.8%, although the best olive oils should not exceed 0.3%
Acidity cannot be detected using taste or smell
Pungency is confused with acidity
How does olive oil acidity originate
To a proportion of 98 %, olive oil is made out of triglycerides. Triglycerides are the main constituents of body fat in humans and other vertebrates, as well as vegetable fat. Think of them as a vertical frame (called glycerol) to which three acids can be attached (hence the tri)
There are three types of fatty acids in olive oil:
Saturated fatty acids (stearic acid) - about 8 - 14 % of total fatty acids
Monounsaturated fatty acids (oleic acid) - 65 - 85 %
Polyunsaturated omega 6 fatty acids - linoleic acid - 6 - 15 %
Polyunsaturated omega 3 fatty acids - alpha-linoleic acid - 0.2 - 1.5 %
Free fatty acids are acids that are "trimmed" from their foundation, their support, that being the triglyceride. Upon that they become weaker, since they are floating free, and are not bound to the glycerol supporting frame anymore. Free acids become prone to oxidation, which in turn, will have a final expression in the rancid taste of some doubtful qualitative olive oils.
This reaction originates in a process called "lipolysis", which initiates at the moment that the oil part makes contact with lipase (enzymes) present in the pulp or seed of the olive. This happens when the integrity of the olive is affected, which can occur in the process of milling (separation of oil from pulp and removal of water, which the sooner it happens, the better for the oil, see below) , but also as a result of:
broken olives
unhealthy olives
olives attacked by microorganisms, diseases, flies
improper storage which leads to alteration of the olive's integrity
It is important to understand that lipases are active only in the presence of water. When water is separated by centrifugation, the process of lipolysis will stop.
Importance of olive oil acidity from a nutritional point of view
As described above, the acidity of olive oil refers strictly to the proportion of free acids in the total oleic acid. But why is this acid so important? It is important because:
Unsaturated fats have a lower melting point than the human body temperature (13 degrees Celsius in the case of oleic acid) , and are liquid in the body, and increase the HDL (the good cholesterol) at the same time reducing the LDL (bad cholesterol)
Saturated fats have a higher melting point (69 degrees Celsius), so they are solid in the body, affecting blood circulation, sticking to the arteries, and are responsible for the LDL (bad cholesterol)
The "seven countries study" and the importance of monounsaturated fats in olive oil
Lots of scientific studies, beginning with the "seven countries study", analyzing the life expectancy of inhabitants from different countries, showed that it was not the total fat intake that increased the life expectancy, but the types of fat. These studies proved that mediterranean nutrition, based on at least 40 % fat per day (out of olive oil) increased life expectancy considerably, and decreased the risk of heart and coronary diseases. This was due to the monounsaturated fats in olive oil!
Mono and polyunsaturated fats decrease LDL and increase HDL, and lower the risk of coronary and heart diseases considerably
So you're looking for a lot of unsaturated acids, as much as possible not floating as free acids.
Here comes the problem: because of their molecular structure, unsaturated fats are more prone to oxidation. Let's look at this in detail.
Importance of type of fatty acids in olive oil
A fatty acid is a chain of carbon atoms, 4 to 30 atoms long, which may be fully saturated by hydrogen atoms (saturated fats), or may miss on some of the hydrogen atoms (monounsaturated if there is only one bond missing, polyunsaturated if several are missing)
(Source: The extra virgin olive oil handbook - Wiley Blackwell - Triglycerides and fatty acids)
Molecular structure of saturated fats
Saturated fats (as butter, animal fat) are linear atom chains, that due to their uninterrupted form stack together tightly in crystals. This is the reason why butter stays solid at room temperature.
You have to think here of playing Tetris: the straighter the lines, the more you can stack.
This is how a saturated fat looks like.
(Source: The extra virgin olive oil handbook - Wiley Blackwell - Triglycerides and fatty acids)
Molecular structure of monounsaturated fats
When down the atom chain, two hydrogen atoms are removed from a carbon atom, the chain is called "unsaturated". If this happens only ones, it is called "monounsaturated" At the same time, when this happens, a bend occurs in the chain, that makes it look like this
(Source: The extra virgin olive oil handbook - Wiley Blackwell - Triglycerides and fatty acids)
The position where the chain is bent now becomes sensitive to oxidation!
Molecular structure of polyunsaturated fats
The more bends there are, the more reactive the fatty acid will be to oxidation, which has an effect not only on the oil itself, but on the body as well, since it increases the risk of cell oxidizing
So there you have it
Olive oil acidity is the number one quality characteristic in a virgin olive oil
Acidity refers to the percentage of free fatty acids on the basis of oleic acid, which is the main fatty acid of olive oil.
An extra virgin olive oil must not exceed 0.8 % acidity. High quality extra virgin olive oils have an acidity under 0.3 %
Acidity cannot be detected using taste and smell
It is triggered by a process called lipolysis, which occurs because of bad olives, improper or long storage of olives, olives affected by diseases
Processing healthy olives as soon as possible will radically reduce acidity, since the process of lipolysis stops when water is separated from oil by centrifugation
Free fatty acids create the premises for further oxidation which may have an effect on taste
Free fatty acids in your body react to oxidation, which give birth to free radicals
Oxidation leads eventually to rancidity, which...well, you don't really want to taste, do you?
There you have it, leave any comments or questions. We'd be happy to answer them for you. aaa
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