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EXTRA VIRGIN OLIVE OIL: HOW DO YOU OPTIMISE THE EXTRACTION PROCESS?

Striking a balance between quantity and quality is the greatest challenge for research in the field of extraction technologies for extra virgin olive oil.

 

Even though in recent years, attention has gradually shifted to quality, obtaining high extraction yields remains a priority for millers and olive growers in order to optimise farm economics.

 

 

 

EXTRACTION: PROBLEMS AND KEY FACTORS 

Only a high extraction yield can pay back a year of hard work the costs incurred looking after the olive trees, but it is not easy to work this way. In fact, it is well-known that in the olive oil production process, in order to improve extraction yields, you often need to extend malaxing times or, alternatively, increase process temperatures. However, this compromise may, in turn, decrease the polyphenol content and reduce the organoleptic qualities and health benefits of the end product.

 

This is also due to the fact that current malaxing machines, in terms of their system, are inefficient heat exchangers.

 

But if it is true that the yield is the result of the oil extraction process, it should not be forgotten that the factors on which one can act to increase it, without affecting the quality of the product, can be of different types:

 

  • agronomic factors, which indirectly affect the olive tree; 
  • technological factors, i.e. specific methods that can be used at the olive oil mill during olive processing.   

 

 

THE AGRONOMIC FACTORS THAT INFLUENCE EXTRACTION YIELDS 

The extraction yield of extra virgin olive oil can be influenced by various parameters, such as lipogenesis, the preservation of the aromatic component and the harvest.

 

Lipogenesis 

To optimise extraction and produce high-quality oil by using agronomic factors, you need to really understand the concept of lipogenesis, i.e. the oil accumulation and biosynthesis process, where lipid molecules are produced by the plant and stored in the seeds (about 1-2%) and in the pulp (the biggest part).

 

Lipogenesis is not an equal, constant factor for all olive plants, but rather a real characteristic dictated by genetic factors that changes based on the cultivar and can be heavily influenced by the environmental conditions of olive growing and the seasons, such as pruning, exposure to the sun, the temperature, rainfall and the wind.

 

All these factors, together with the genetics of the cultivar, ensure that peak lipogenesis (when the highest amount of oil is accumulated in the fruit) does not always correspond to the same time of ripening every year.

 

The preservation of the aromatic component 

In fact, we should not forget that the quality of the oil is heavily influenced by the sensations detected from its smell and taste, which are expressed with a relatively intense fruitiness that represents the flavour of the olives based on the cultivar and growing area. 

 

The aroma of virgin oil is formed by a complex blend of volatile compounds, aldehydes, alcohols, ketones, hydrocarbons and esters, which can be easily lost during veraison of the fruit due to oxidation, but also in the various processing steps if they are done too slowly or at high temperatures.

 

It is therefore proven that from olives harvested at an early stage of ripening, you get intensely fruity, green, bitter and spicy oils, while from olives harvested at an advanced stage of ripening, you get oils with a less intense, less bitter, ripe fruitiness.

 

 

The importance of the harvest

The end of lipogenesis is therefore the best time to harvest olives and to press them. This is because, as the ripening progresses, there is an increasing imbalance in the ratio between the quantity of oil and the aromatic component.

 

To achieve high yields and to optimise processing times by using agronomic factors, it is important to assess the harvest time every year, not based on the ripening, but on the oil accumulation process inside the olives. At the same time, this will help produce a product with the best organoleptic properties possible without sacrificing the aromatic quality.

 

 

THE TECHNOLOGICAL FACTORS THAT INFLUENCE EXTRACTION YIELDS 

The technological principles that affect the extraction yield are linked to the structure of the olive’s cell wall and to the presence of pectolytic enzymes.

 

 

The structure of the cell wall 

The compromise that you have to accept when harvesting olives at peak lipogenesis is that, depending on the year, you may find that you are processing fruit that still has very solid, compact pulp.

 

This is because the hardness of the fruit is caused by the layers of pectin that form the plant cell walls and help maintain the tissue structure. Pectin cements the space between one cell and another, keeping them together and making the pulp crunchy. During ripening, pectins are hydrolysed or broken down by the action of the endogenous enzymes naturally found inside the fruit, and this causes the pulp to lose its structure and the fruit to soften naturally.

 

When the concentration of pectin in the cell walls is very high, just like in olives harvested at an early stage of ripening, it can therefore be particularly difficult, and inefficient, to extract the oil found inside the mesocarp cells. In fact, during the initial ripening stages, the plant’s endogenous enzymes have not yet developed.

 

Furthermore, a second function of endogenous enzymes is to oxidise the phenolic component in order to encourage the skin to turn brown, which helps defend the fruit and the genetic material inside the seeds from solar radiation, although it also loses the aromatic component.

Pectolytic enzymes 

As a result of all these factors, the use in malaxing phase of exogenous enzymes with pectolytic action has been observed in various circumstances, i.e. enzymes that depolymerise pectins and cause the maceration of tissues, could be helpful in increasing oil extraction efficiency even on unripe olives.

Exogenous pectolytic enzymes, added during the malixing, would work on the pectin present in the cell walls and thus disintegrate the pulp, allowing easier extraction of the oil, but without affecting the aromatic component. Their action would thus theoretically shorten the time and lower the temperature of malaxing.

In fact, high temperatures and long malaxing times irreparably compromise the aromatic and phenolic structure of oils, which results in the loss of the fruity aromatic note.

 

 

AEB’S CONTRIBUTION: FIELD TRIALS 

Numerous tests were carried out for experimental purposes at various oil mills by the University of Bari (Italy) and the University of Jaén (Spain), have proven that the combination of agronomic and technological factors can have excellent results in terms of increasing yields during extraction.

 

Harvesting the olives at the peak of their lipogenesis in combination with the use of selected enzymes acting only on the pectic component, would allow the producer to obtain not only a larger amount of oil for the same weight of harvested olives but, above all, a much more fragrant oil with bolder, more intense aromatic notes.

 

The data collected from the experimental tests showed that, with the use of exogenous enzymes, it would be possible to increase the efficiency of the whole process of  malaxing and centrifugation. The data collected by the universities showed a considerable difference emerged between the malaxing carried out with or without exogenous pectolytic enzymes: in fact, even after a few minutes from adding the enzyme, the oil starts to surface above the paste during malaxing, a phenomenon which – without the use of enzymes – only happens from halfway through the malaxing process.

 

 

 

 

WHAT COULD BE THE POTENTIAL BENEFITS?

  • Higher extraction
  • Smoother workflow by the malaxing machine
  • Less handling of the paste
  • Greater energy efficiency with a subsequent reduction in consumption

 

 

 

Video of a comparison between two malaxing machines 

Experimental tests carried out at several Italian oil plants

Impianto di gramolatura in funzione

Operational malaxing system

Gramola con pasta di olive

Malaxing machine with olive paste

Dettaglio della gramola con pasta di olive in fase avanzata

Detailed view of the malaxing machine with olive paste at an advanced stage

Affioramento dell’olio extra vergine in lavorazione

The extra virgin oil rising to the surface during processing

Uscita dell’olio dalla centrifuga di separazione

The oil flowing out after centrifugal separation

Raccolta del prodotto finito

Collecting the end product

Graph of the increased extraction yield using exogenous enzymes