The olive oil acidity is a parameter used to measure its quality. In the past, acidity was the main indicator of quality, the valuation of olive oil in the tasting panels being unnecessary.
Although other characteristics of olive oil are currently evaluated, acidity remains the benchmark.
In this publication we will analyze:
- What is the olive oil acidity.
- The conditions that vary the degree of acidity for olive oil.
- How an acidity analysis of the oil is performed (Material and calculations).
- And how the acidity of the oil is reduced.
What is the olive oil acidity?
Olive oil is made up of different fatty acids (oleic acid (O), linoleic (L), stearic (E), palmitic (P) These fatty acids are combined to form triglycerides (OOO, OOP, OPO, POO, LOO, OLO, OOL, OLP, POL, PLO , LOP, OOE, EOO, POP) The most common in olive oil is triolein (OOO), formed by the union of three chains of oleic acid.
Lipase enzymes break down triglycerides into glycerol and free fatty acids. During this process, the oils deteriorate and get dirty. The degree of acidity, therefore, warns of the state of degradation that presents a olive oil.
The calculation of the acidity of fats is called % free oleic acid. Although, in the result of the analysis, volatile acidity of all fatty acids is included. Regardless of the vegetable oil (olive, sunflower, coconut, palm oil…) the use of % acid is supported oleico libre in the acidity analysis. This is because there are no significant differences in density between fatty acids.
Degree of acidity for the olive oil
There are several factors that influence the degree of acidity that an olive oil has.
- Quality of harvested olives: Some olive pests and diseases decrease the quality of olives Pests such as the olive fly and diseases such as soapy olive, worsen the characteristics of the olive, increasing the acid number of the oil.
- Time of harvesting olives: As the harvest is delayed, the olive ripens and gradually deteriorates, increasing the degree of acidity for the olive oil obtained.
- Damages during harvesting, storage and transport: wand collection, olive harvesters or mechanized harvesting, produce different wounds in the olives. Some can also get crushed. Damaged olives deteriorate in a short time and increase the degree of acidity. Therefore, whenever possible, it is advisable to bring the olives to the mill every day.
- Climate damage: The incidence of hail and frost is the main problem facing the olive tree. On the other hand, the soil olive is more affected by moisture and fungal attack.
- Storage in the mill: In the mills the time between cleaning olives and grinding should be as short as possible. The capacity of receiving olives from an oil mill is greater than that of milling. Due to this, the olive once cleaned, is stored in hoppers. During storage, the olive deteriorates and the acidity index of the oil can be increased by one or several tenths per day, depending on the conditions. In addition, it favors the appearance of defects in olive oil. Therefore, the best olive oils seek to minimize the time between olive harvesting and olive oil extraction.
How to calculate the degree of acidity?
Calculate the degree of acidity for olive oil, it is simple if you have the appropriate reagents and materials.
Before it was common among olive growers to have these equipment, to perform their measurements at home.
The following method would also help us analyze other vegetable fats (sunflower oil, palm, coconut, corn, soy…).
Materials needed to measure the acidity of the oil
These are the materials used to measure the degree of acidity.
- Precision scale: We will use a precision scale, with a margin of error of 0.01 g.
- Erlenmeyer flask: Widely used in laboratories, this glass container has a wide base and narrow mouth. Its shape favors the mixing and agitation of products, making it difficult to spill liquids. Other types of jars with mixers can also be used.
- Burette: Elongated glass container, used to make precise volume measurements. The precision syringes can also be useful for this.
- Phenolphthalein: Used as a pH indicator. In acidic medium it is transparent, however, its color changes to pinkish tones when the solution becomes basic.
- Ethyl alcohol or Ethanol: It is used as a solvent for olive oil. Currently, you can buy ethanol with added phenolphthalein, more convenient for acidity analysis.
- Caustic soda solution (NAOH): The caustic soda, not only serves us for sweeten the olives or make homemade olive oil soap, it will also allow us to know the acidity of olive oil. For this, it is necessary to know exactly the concentration of the solution. To make the solution, it is important to know that the molecular weight of caustic soda is: 39,997 g / mol.
How is the degree of acidity for olive oil calculated?
To measure the acidity of the oil, it must be taken into account that one mole of free oleic acid C18H34O2 (282.47 g), reacts with one mole of caustic soda. During the reaction, the oil-free fatty acids are neutralized, increasing the pH, which goes from being acidic to basic.
M Ac.oleic =V NaOHx N NaOHx PM Ac.oleic
% Degree of acidity = M Ac.oleicx 100 / V OilAnalizedx D Oil
Steps to follow to calculate the degree of acidity
- Weigh 10 grams of olive oil.
- Place 20 ml of ethanol in the Erlenmeyer flask. Approximately 2 ml of ethyl alcohol is needed to dissolve 1 g of olive oil. Although, if we want, we can add a little more.
- Add a few drops of phenolphthalein, if it is not included in ethyl alcohol.
- Ethanol has a pH of 6, we add drops of NaOH solution, to raise the pH to 8.2. In this way, we will see how the solution becomes slightly pink by phenolphthalein. The color must remain permanent for 8-30 seconds, for this purpose it is added dropwise while stirring.
- Mix olive oil with ethanol.
- The solution will remain transparent, since the pH of the oil is acidic and the phenolphthalein becomes transparent again.
- We measure with precision the solution of soda and we are slowly adding and stirring until the pink color remains visible for about 8 seconds.
- Taking the ml spent in step 7, we calculate the degree of acidity of the olive oil.
Example to calculate the degree of acidity
– Taking into account that 1.2ml of NaOH is used at 0.1N to neutralize the volatile acidity of 10 grams of olive oil. What is the acidity grade of olive oil?
- We calculate the moles of NaOH consumed: 0.1 mol/liters x 0.0012 liters = 0.00012 moles.
- Then, we calculate how much 0.00012 moles of oleic acid weigh: 0.00012 x 282.5 g / mol = 0.0339 grams.
- We multiply the previous value by 100, since we have used 10 grams of oil, to calculate the grams of volatile acidity of 1 kg of olive oil. Resulting 3.39 g oleic acid per kg olive oil.
- We pass the value to Kg and multiply by 100, to calculate the% of free oleic acid 0.34%.
- Extra virgin olive oil acidity: The highest quality olive oil must have less than 0.8 degrees of acidity. In addition to this, you need to pass a tasting panel and have no organoleptic defect.
Simplify calculations: rapid acidity measurements
The previous method is improvable, since if we are going to perform multiple analyzes, the simplification of the calculations is convenient.
For this, what is done is to calculate the grams of oil that we would have to dissolve so that 0.1 ml or 1 ml of NaoH is equivalent to 1 tenth of acidity of the oil.
In this way, jobs can be mechanized more and the result is obtained directly.
Important: For low acidity olive oils such as the EVOO it is recommended to use a solution 0.1 mol / liter. In the case of lampant olive oils it is preferable to use solutions with 0.5 N.
NOTICE: Currently, to calculate the degree of acidity of fats, laboratories follow the ISO 660: 2009 standard. In this standard, Potassium Hydroxide (KOH) is used instead of caustic soda (NaOH).
How to reduce acidity in olive oil?
The olive oil acidity can be reduced through the refining process. In fact, refined olive oil has no acidity, since it is neutralized by different chemical processes (neutralization with soda) and physical processes. The problem is that by refining olive oil, we not only eliminate acidity, we also get rid of other volatile components of olive oil. Therefore, we lose part of the positive properties that virgin olive oils provide.
We have translated the information on our website from Spanish to English. Note that some words may have seen their meaning altered during their translation.