THE KEY QUALITY INDICATORS
There are different organisations which regulate the classification of olive oils across the world and therefore there are slight differences in their requirements. However, when it comes to classifying Extra Virgin Olive Oils, there are certain requirements for the production method and chemical composition which remain universal. These are:
A VERY LOW ACIDITY LEVELS
Acidity is the basic indicator of the quality of virgin olive oil and this simple knowledge will help you easily differentiate between virgin oil types. Extra Virgin olive oils must not have more than 0.8 grams of oleic acid per 100 grams - expressed as an acidity level less than or equal to 0.8%
Fatty acids occur naturally in olives and when the fruit is in perfect condition, these are bound in triglycerides making them neutral in terms of acidity. However, if the fruit is damaged or pressed too late in the season, the cell walls break down releasing the fatty acids and increasing the acidity of the oil.
High acidity levels negatively affect the taste as the oil is more likely to oxidise and have a rancid taste. Any error in the handling or cultivation of the olives will increase this and that is why acidity is such an important indicator of quality.
The best Extra Virgin olive oils tend to have an acidity level of around 0.25%. The Extra Virgin olive oils we select have a maximum acidity level of 0.1% - well below the 0.8% requirement making these truly exceptional.
NB: It is important to note that the acidity indicator is only relevant when assessing Virgin olive oils and not for oils which have been artificially refined. During the refining process, free fatty acids are eliminated through chemical processing.
Extra virgin olive oil: acidity ≤ 0.8%
Virgin oil: acidity ≤ 2.0%
Refined olive oil: acidity ≤ 0.3%
Olive oil (Blend of refined and virgin oil): acidity ≤ 1.0%
LOW LEVELS OF PEROXIDATION
Peroxidation is a quality parameter that indicates how much the olive oil has been exposed to, and damaged by oxygen. The level of peroxides in the oil cannot exceed 20 milliequivalents per kilogram.
Lipid Oxidation is the main cause of deteriorative changes in the chemical, sensory, and nutritional properties of edible oils. The best olive oil producers use specialist equipment to carefully control the amount of oxygen present throughout the production process. These oils typically will have a peroxidation of less than 10.
A VERY LOW WAX CONTENT
Another very important quality indicator is the presence of waxes in the oil. The maximum permitted value of waxes in Extra Virgin and Virgin olive oils is no more than 150g / Kg.
Waxes are naturally present on the leaves of the olive tree and form a protective layer on the olives themselves. Normally, this wax remains in the leftover pulp during the first pressing.
However, if the pulp is pressed for a second time or if excessive heat or chemicals were used during the extraction process, this will be revealed as a higher proportion of wax content of the oil.
Natural oils that are mechanically extracted do not contain fatty acids chains as they are not present in pure and freshly extracted olive oils.
These fatty acid chains have a high UV absorbance and if present, can be measured scientifically using Spectrophotometry.
As part of the quality control process, Virgin olive oils are analysed this way showing UV absorption at 232nm (known as K232) and 270nm (known as K270). Generally, K232 increases due to the inappropriate storage of olives and K270 increases when the oil is not fresh. Delta K is an additional measure of purity as it indicates the presence of refined or pomace oils.
These scientific measures form an accurate indication of oil quality, purity and oxidisation. The legal maximums as stated by the IOC (International Olive Council) are as follows:
Delta K ≤0.01