Olive oil acidity: what laboratory analysis really measures

Of all the figures surrounding olive oil, none is misinterpreted as much as acidity. Half of people think it measures how acidic it tastes; the other half thinks the lower it is, the better the oil. Both are wrong.

TL;DR: Acidity measures the free fatty acids in the oil, expressed as a percentage of oleic acid. It has nothing to do with whether an oil tastes strong, stings, or is bitter: it is imperceptible to the palate and can only be determined in a laboratory by titration. Extra virgin cannot exceed 0.80. But acidity alone does not say whether an oil is good, and that is why European regulations prohibit it from being indicated on the label unless accompanied by peroxides, waxes, and ultraviolet absorbance.

In class I always spend some time on this because it is the most expensive misunderstanding a buyer can make: it leads to paying for a number that does not mean what it seems.

Let's move on to what it does measure, and to the rest of the laboratory analysis, which is where the real information is. If you are looking for how to choose an oil with the label in front of you, that is in EVOO: what it is, what it is for, and how to choose it.

What acidity measures exactly

Every campaign I see a lot of laboratory analyses of the oils I produce for our clients. This is what I am looking at when I look at it.

Olive oil is, almost entirely, triglycerides: molecules with three fatty acids attached to a glycerol. When the olive is damaged—by the strike of the pole, by the fly, by waiting days piled up, by fermenting—its own enzymes, the lipases, start to break those bonds. Each break releases a fatty acid.

Acidity is the amount of free fatty acids, expressed as a percentage by weight of oleic acid, which is the majority in olive oil. 0.3% acidity means that 3 out of every 1,000 grams are free fatty acids.

That is why acidity does not speak of flavor: it speaks of the condition in which the olive arrived at the mill. It is an indicator of damage and time, not of sensory quality. When I see a high number I do not think "this will taste bad", I think "someone took too long here".

Why it is not tasted

Here is the point I want to make clear, because it circulates poorly explained even in the sector.

Free fatty acids, at the concentrations found in olive oil—below 2%—are odorless and tasteless. They do not produce the sensation of acidity that a lemon or vinegar would give. They cannot be detected by tasting. Not even an official panel can tell you the acidity of an oil by tasting it: a laboratory is needed.

What you do perceive—bitterness, spiciness, fruitiness—comes from polyphenols and volatile compounds, which have nothing to do with this measure.

Now the honest nuance, which almost no one adds: that acidity is not tasted does not mean it does not matter. High acidity is usually accompanied by defects that are indeed perceptible, because both things have the same cause: damaged or fermented fruit. Acidity is not the defect; it is the trace left by the same problem that causes it. That is why it correlates with quality without being a measure of quality.

How it is measured in the laboratory

The method is an acid-base titration, and it is one of the simplest in all of oil analysis. So simple that it is surprising, coming from a piece of data that is given so much commercial importance.

A sample of oil is weighed and dissolved in a mixture of solvents. An indicator—phenolphthalein—is added and a solution of potassium hydroxide of known concentration is dropped in, drop by drop. The alkali neutralizes the free fatty acids. When there are none left, the next drop turns the solution pink again, and that is where it stops.

That color change is what everyone who has ever done it remembers most: for a good while absolutely nothing happens, and suddenly, with a single drop, the entire flask turns pink. That is where the measurement ends. With the volume spent, it is calculated how many free acids there were, and the result is expressed as grams of oleic acid per 100 grams of oil, which is the same as that "%" on the label.

I want you to keep the scale of the thing in mind: acidity is determined with a burette and a flask. Expensive equipment is not needed, and that is why many mills measure it at home during the campaign. The parameters that come after no longer: those require a real laboratory, and that is precisely the difference between knowing the acidity of an oil and knowing what that oil is like.

The legal limits, category by category

This is the table of quality characteristics of the Delegated Regulation (EU) 2022/2104, which is the current standard:

Notice one thing that surprises many people: refined oil has the lowest acidity on the table, a maximum of 0.30, stricter than extra virgin. It is logical—refining chemically neutralizes free acids—and it demonstrates by itself that low acidity does not mean quality. If acidity measured how good an oil is, refined would beat everyone.

And vice versa: an extra virgin oil can pass the chemical analysis with room to spare and still not be extra virgin, because it lacks the tasting panel. I tell that part in virgin and extra virgin.

The rest of the analysis: what acidity does not see

Acidity only looks at one thing: hydrolysis. The complete analysis looks at several more, and each parameter detects a different problem.

Peroxide index. It measures oxidation in its initial phase: how many peroxides have formed by reaction with oxygen. It is the parameter that ages with the oil. A freshly made extra virgin is usually far below the limit of 20; as the months pass, it rises.

K232. Ultraviolet absorbance at 232 nanometers. It detects conjugated dienes, which are early products of oxidation. It goes hand in hand with peroxides and confirms if an oil has started to degrade.

K270 and ΔK. Absorbance at 270 nanometers. Here the most advanced oxidation products are seen, but above all it serves for something else: detecting refined. The refining process leaves a characteristic trace in that band of the ultraviolet. That is why the extra virgin limit is 0.22 and the refined 1.25: if an oil sold as extra virgin gives a high K270, someone has added refined to it. ΔK refines that same detection.

Ethyl esters. The most modern and, for me, the most revealing. They form when the ethanol from fermentation reacts with free fatty acids. Translated: they betray fermented olive, even if the oil has been washed or deodorized afterwards to hide it. An extra virgin cannot exceed 35 mg/kg. It is the parameter that was introduced precisely to catch "fixed" oils.

Waxes. They are not in the quality table but in the purity one, and they serve to detect mixing with olive pomace oil, which has many more.

The degrees: what that "0.4°" and that "1°" were

For decades, the labels on the Spanish shelves indicated "olive oil 0.4°" or "1°". That degree was the acidity.

I saw those bottles at my friends' houses, never at mine: being Marino Uceda's daughter, having a "1°" in the kitchen would have been a mortal sin. But outside the house they were everywhere, and with them came the inherited idea that 0.4 was the good one and 1 was for frying. An entire generation learned to buy oil with a scale that did not measure what it seemed to measure.

They stopped being used for a concrete reason, and the European regulation says it in all its letters. Delegated Regulation (EU) 2022/2104 justifies it thus: acidity, mentioned in isolation, "falsely makes one think of an absolute quality scale that is misleading for the consumer".

And it does not stop at the statement of reasons. Its article on labeling establishes that the indication of acidity can only appear if accompanied, in characters of the same size and in the same visual field, by the maximum values of peroxides, wax content, and ultraviolet absorbance.

That is: European law explicitly recognizes that acidity alone deceives, and forces it to be accompanied by the rest. If you see a bottle that boasts acidity without the other three data next to it and of the same size, that label does not comply.

The detail that almost no one knows: the values are the ones at the end

There is one last twist, and it is one of those that separate who has read the regulation from who repeats it. I discovered it reading the regulation to prepare a class, and it changed how I look at the bulletins.

When those parameters are indicated on the label, the figure that must appear is not the one from the day of the analysis: it is the maximum value that that parameter can reach on the minimum duration date. That is, the worst value expected at the end of the oil's useful life, not the best at the beginning.

It makes perfect sense, because peroxides and K232 rise over time. And it explains why a serious producer is not interested in boasting about a 0.1: he would have to guarantee that number until the best before date.

Is a 0.1 better than a 0.3?

I give you my opinion, and I mark it as what it is: an opinion of a taster, not an article of the regulation.

Below a certain threshold, acidity stops discriminating. Between a 0.1 and a 0.3 there is no difference you can perceive, nor any that predicts which of the two you will like more. Both indicate the same: healthy olive milled quickly. From there, what decides is the variety, the time of harvest, the work of the mill, and how the bottle has been stored.

Chasing tenths of acidity is like choosing a car by the thickness of the paint. It measures something real, but not what matters to you.

How to know the acidity of the oil you have at home

With the bottle in front of you, the short answer is that normally you cannot. Indicating acidity is voluntary, and as we have just seen, doing so forces you to put other three parameters, so the majority of packers do not indicate it.

What you can do:

• Ask the producer for the analysis. It is what I do before putting an oil in the oleoteca: any serious mill has the bulletin of each batch and shows it without problem. Whether they give it to you, or give you the runaround, already tells you a lot.
• Look at the harvest campaign. It is a much more useful piece of data than acidity, and also voluntary. It can only be indicated if 100% of the content comes from that harvest, so when it appears it is reliable. In Spain it is still optional.
• Trust your nose. For what acidity does not tell you—if the oil is good—you have a free instrument. How to use it is in how to taste olive oil.

This article is part of our guide to understanding olive oil.

References

• Delegated Regulation (EU) 2022/2104 of the Commission, by which Regulation (EU) No. 1308/2013 is completed in what regards the marketing standards of olive oil: Annex I (quality and purity characteristics), conditions for indicating acidity on the label and for indicating the harvest campaign.
• Implementing Regulation (EU) 2022/2105, on the conformity controls and the analysis methods of the characteristics of olive oil.
• Regulation (EEC) No. 2568/91 and its successive modifications, historical origin of the analysis methods.
• Royal Decree 760/2021, by which the quality standard of olive oils and olive pomace oil is approved.

Frequently asked questions

What is the acidity of olive oil?

It is the amount of fatty acids that have been released from the triglycerides of the oil, expressed as a percentage by weight of oleic acid. It is produced when the olive is damaged or ferments and its own enzymes break those bonds. That is why acidity does not inform of the flavor: it informs of the condition in which the fruit arrived at the mill. 0.3% means that 3 out of every 1,000 grams are free fatty acids.

Is the acidity of olive oil noticeable when tasting it?

No. Free fatty acids, at the concentrations found in olive oil, are odorless and tasteless: they do not produce the acidic sensation of a lemon or vinegar and cannot be detected by tasting, not even by an official panel. What is indeed perceived—bitterness, spiciness, and fruitiness—comes from the polyphenols and volatile compounds, which have no relation to this measure.

What acidity does extra virgin olive oil have?

A maximum of 0.80%, according to Annex I of Delegated Regulation (EU) 2022/2104. Virgin allows up to 2.0% and above that value the oil is lampante. It is worth knowing that refined oil has an even lower limit, 0.30%, precisely because refining chemically neutralizes free acids: it is the proof that low acidity does not equate to quality.

How is the acidity of olive oil measured?

With an acid-base titration. A sample is weighed, dissolved in a mixture of solvents, phenolphthalein is added as an indicator and a solution of potassium hydroxide is added drop by drop until the mixture turns pink. With the volume spent, the amount of free fatty acids is calculated, which is expressed in grams of oleic acid per 100 grams of oil. It does not require expensive equipment, unlike the rest of the parameters.

Why are the degrees 0.4° or 1° no longer seen on the labels?

Because European regulations consider that acidity indicated in isolation "falsely makes one think of an absolute quality scale that is misleading for the consumer". Delegated Regulation (EU) 2022/2104 allows it to be indicated, but only if accompanied, in characters of the same size and in the same visual field, by the maximum values of peroxides, wax content, and ultraviolet absorbance.

What other parameters does the analysis of olive oil include?

The peroxide index, which measures initial oxidation. K232, which detects the conjugated dienes of that same early oxidation. K270 and ΔK, which reveal advanced oxidation and, above all, the presence of refined oil. Ethyl esters, which betray fermented olive even if the oil has been deodorized afterwards. And waxes, which serve to detect mixing with olive pomace oil.

Is an oil with acidity 0.1 better than one with 0.3?

Not in an appreciable way. Below a certain threshold acidity stops discriminating: both values indicate the same, healthy olive milled quickly, and neither predicts which of the two oils will be liked more. What decides the difference is the variety, the time of harvest, the work of the mill, and the storage of the bottle.