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April 2017
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Olive harvesting systems have a significant effect on the quality of the oil which comes from these berries. In the majority of cases, the olives from olive tress with big branches (the average is 5m but they can get up to 12m long) fall to the ground as they mature and are collected from the ground for crushing. In olive groves situated in difficult to reach areas due to steep slopes, or those in areas like Brindisi, Lecce or the Gioia Tauro plain where the plants can be very tall, nets are put up around the trunk. However, this net system often means that extra virgin olive oil cannot be made as the olives are too mature as too much time passes between falling on to the net and being collected.
The level of freshness and integrity of the olives differs according to the amount of days that pass from when the first olives fall off the tree and the last ones, which create a more acidic oil.
In olive oil production areas where the level of acidity is very low (which produces the finest oils), harvesting is done by hand, directly from the plant (stripping), but it is carried out exclusively in family-run olive companies and those that are quite small (up to 50 plants).
Therefore today, the majority of olives are harvested mechanically which has noticeable, positive repercussions from both an economic and a qualitative point of view. Mechanical harvesting takes less time than traditional, manual picking and means that harvesting can be programmed when the olives are at the right degree of ripeness or veraison (when the olive is half green and half black). Furthermore, with modern, mechanical harvesting systems, we no longer have to wait for olives to fall, nor be collected from the floor, thus positively influencing the quality of the oil.
The olives that are taken for crushing must be milled in the shortest amount of time possible so that the organoleptic qualities are not affected. Once they are crushed, the olives leave a ‘residue’ which makes up 40% of their original weight, and which in the past was used for heating as it contains pulpy residues and fragments of the stone, which are very good fuels. Nowadays however, with the help of chemical solvents, ‘residue oil’ is extracted, which is of the lowest quality. Until a few decades ago, this ‘residue oil’ was used almost exclusively for the production of soap and candles however, when the soap industry moved to the chemical industry and they used man made substances, this residue began to be used in the production of olive oil which, when treated and mixed with virgin oil, is edible.

Acidity as an indicator of quality
Acidity is one of the parameters that indicates the percentage of oleic acid in an oil and is the main indicator of quality. The higher the value, the poorer the quality of the product. The acidity is the direct consequence of the release of fatty acids caused by the phenomenon of hydrolysis of glycerides and it is a qualitative parameter which can only be defined via laboratory testing. This parameter also means that any changes that happen to the olives and oil during harvesting, transportation and crushing can be tested.
Determining the acidity is done in laboratories and it consists of a simple analysis which almost all mills can now do independently. For the exact definition of the concept of free acidity, it is important to highlight that extra virgin olive oils are made up of 98-99% triglycerides, that is esters derived from glycerine and fatty acids. Some of these latter esters remain free however, not combining with glycerine, thus determining the acidity of the product.
Free fatty acids in oil can be increased if a specific enzyme, called lipase, which can be found in fruit, acts on them and this process can be activated if the drupe has damage to its cells (attacks from insects/damage during harvesting and transportation/bad environmental conditions). The enzymatic function of lipase is further aided by quite high temperatures, around 30-40°C.
We can therefore conclude that the grade of acidity of an oil is strongly influenced by the health of the olives, the harvesting technology, storage time, the processing technology used (for example, very high kneading temperatures) and the care taken by operators when handling or storing the product.
Olive oil is classified as Extra Virgin Olive Oil when its free acidity is lower than 0.8g/litre.

Number of peroxides
This is an indicator of the primary oxidation of the oil and is measured through the quantitative analysis of the hydroperoxides, the formation of which occurs in enzymatic reactions of lipoxygenase, which is present in olives, or because of free radical reactions which are aided by oxygen in the oil. This analysis is carried out in laboratories, even though recently some tools have been made that make this very easy and cheap to do. As mentioned, the state of primary oxidation of an oil depends on the enzymatic activity of the lipoxygenase, which reacts if the pulp of the drupe is damaged in any way, as well as the contact the oil has with oxygen in the air, which causes oxidisation of fatty acids and the formation of peroxides. In both cases the amount of contact the oil has with oxygen needs to be reduced.
The care taken when choosing and harvesting the olives, the harvesting methods and times and the attention paid to storing and preserving the product all affect this parameter.
Normally, oil, which has just been produced, has a varying value of peroxides that ranges from 2-5meq/kg. These values tend to increase during preservation and, if the oil is preserved without air, once all the oxygen that is present in the oil has been used, the value can reach 20meq/kg.
These values give us the final estimate of the authenticity of an oil. On average, these values can be calculated 15-20 months after production therefore oil cannot be stored and preserved, away from air and light, for any longer than this amount of time.

Ultraviolet spectrophotometric absorption
In order to evaluate the spectrophotometric absorptions of extra virgin olive oil, a special instrument is used, called a spectrophotometer, and this type of analysis is carried out in a laboratory. The results depend on the oil’s absorption abilities which, in turn, depend on both the oxidation level and possible industrial adulterations that the oil is subjected to. This is why these values indicate the quality of the oil.
The analysis is based on the ability of an oil sample to absorb radiant energy with wavelengths of 232-270 nm. Every oil has a value of K232 and K270 and these values are related to the presence of double and tripe bonds which are created as a result of oxidative processes which oil is subjected to when it is attacked by the oxygen that is present in the air. Moreover, the value K270 is also influenced by secondary oxidation of the oil which comes from the presence of decomposition products of hydroperoxides (aldehydes, ketones), which modify the organoleptic characteristics, giving rise to the famous ‘rancid’ defect.
Normally, the value K232 of an oil that has just been produced can vary from 1.4-1.6, whilst the K270 value varies from 0.09-0.12. As a result of oxidation, these values tend to increase and for products that have been stored well, it is unlikely that they go over 2.5, for K232, and 0.22, for K270 (always measured after 15 months).

Depending on the quality of the olives, their freshness and integrity, the level of acidity and production, olive oils can be categorised as follows:

“Extra Virgin Olive Oil is a superior category olive oil obtained directly from olives and solely by mechanical means.” The free acidity, or oleic acid, of extra virgin olive oil is, at the most, 0.8g/100g and it has other characteristics like those indicated for this category;
“Olive Oil obtained directly from olives and solely by mechanical means.” The free acidity, or oleic acid, of virgin olive oil is, at the most, 2g/100g and has other characteristics like those indicated for this category;
“Olive Oil is an oil comprising exclusively of olive oils that have undergone refining and oils obtained directly from olives.” Olive oil is obtained by blending refined olive oil with virgin olive oil. The free acidity, or oleic acid, is never more than 1g/100g and has other characteristics like those that are indicated for this category. It is the result of mixing a rectified oil, which has undergone a chemical process, that is designed to eliminate chemical and organoleptic defects, and a virgin oil. The law does not require that a minimum quantity of virgin olive oil is used therefore usually only a small percentage is mixed in which is just enough to restore colour, smell and taste to the oil which, on the whole, is quite 'flat';
“Oil exclusively containing oils derived from the processing of the product obtained after the extraction of olive oil and oils obtained directly from olives," or "Oil exclusively containing oils obtained by treating the product obtained after the extraction of olive oil and oils obtained directly from olives." Oil obtained by blending olive pomace oil and virgin olive oil. The free acidity, or oleic acid, is never more than 1g/100g and has other characteristics like those that are indicated for this category.


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