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Thermal conditioning of olive paste comes into the mill contributing to the increase in quality parameters of extra virgin olive oil

The Thermal Conditioning Module consists in a highly efficient tubular heat exchanger installed in the line after the crusher, able to bring down the olive paste temperature immediately before sending it to malaxer for gradual heating and consequent release of oil

During the last few decades Institutions, International organizations and producers have made a major effort to increase consumers’ awareness of Extra Virgin Olive Oil culture, taste quality and health benefits. Simultaneously, the olive oil industry had increased its interest in quality production, fruit selection and differentiation of characteristics in order to satisfy the widest range of consumers and also gain new potential markets.

As is deeply demonstrated in the literature, the fundamental basis to produce excellent olive oil quality and differentiate his characteristics, are in the olive fruit and in particular in healthy fruit at the right stage of ripeness at harvesting. That knowledge helps to move ahead of time year by year the milling period with respect to the usual traditional beliefs of the past. Looking at quality production and moving ahead of time the mill processing period brings the harvest climate closer and closer to the outdoor autumn temperature as opposed to the traditional outdoor winter temperature.

Alfa Laval, a world leader in Olive Oil technology and Innovation for more than 80 years and a leader in separation and heat transfer, in collaboration with the staff of Professor Maurizio Servili at the University of Perugia (Italy), has carried out an investigation on the relationship between the temperature of olives coming into the oil mill and the consequent level of quality olive oil produced. Research clearly demonstrates that olives comes to the mill from early harvest brings olive paste temperature immediately after olive crushing higher than approximately 18°C-25°C (with cases of 28°C-35°C or more) with consequent negative effects on the final content of phenols and volatile compounds of extra virgin olive oil. In effect, the traditional malaxer in the olive mill does not make it possible to handle the paste temperature except for gradual heating up to a prefixed maximum value.

Practically, today, with an increased temperature of olives comes into the mill (due to an autumnal outdoor temperature during early harvest), with the heating of the olive paste from crusher and with the traditional malaxer for olive paste temperature control it is practically impossible to bring to the olive oil bottle all the potential quality that you can get with your olives.

Three years of research by Alfa Laval and Perugia University has developed exclusive new technology equipment named Thermal Conditioning Module and a complete new way to handle temperature during the olive oil extraction process (Patent pending n. EP15183569.1). The Thermal Conditioning Module consists in a highly efficient tubular heat exchanger installed in the line after the crusher (Figure 1), able to bring down the olive paste temperature immediately before sending it to malaxer for gradual heating and consequent release of oil. A secondary use of Thermal Conditioning Module should be dedicated to fast heating up of olive paste when necessary.

Early harvest – Cool down olive paste temperature and preserve the olive oil quality to the top level

Early harvest is more and more important to get top quality extra virgin olive oil. With autumnal outdoor temperature at harvest, olives comes to the mill able to brings olive paste temperature immediately after olive crushing higher than approximately 18°C-25°C (with cases of 28°C-35°C or more). Figure 2 shows a schematic representation of trend of temperature starting from olives at 21°C and processed with traditional mill (red line). After crushing olive paste should goes immediately at 27°C. When we transfer the paste to the malaxer (settled in the example at a maximum temperature of 28°C) practically we don’t need any heating and often is difficult to keep lower than a certain level the maximum temperature.

The immediate thermal lowering of the olive paste temperature after olive crushing to lower than 20°C with the Alfa Laval Thermal Conditioning Module permits partial inhibition of the endogenous enzymatic activity by polyphenol oxidase and peroxidase. The consequence is reduction of degradation of phenolic compounds and/or an increase in the formation of volatile compounds in the final extra virgin olive oil. In particular, the investigation reports a final extra virgin olive oil with an increase in oleuropein derivatives and ligstroside and, in several cultivars, an increase of volatile compounds responsible for the olive flavor such as esters responsible for the “Floreal” sensory notes, without negative modification of C6 aldehydes related to the cut-grass sensory notes . The same Figure 2 shows a schematic representation of trend of temperature starting from olives at 21°C and processed with Thermal Conditioning Module (blue line). After crushing olive paste is immediately cool down until 15°C. When we transfer the paste to the malaxer (settled in the example at a maximum temperature of 28°C) we have a gradual heating and a perfect control of temperature able to preserve quality without negative impact on olive yield with respect to traditional technology.

Late harvest – Heating up olive paste temperature and make faster extraction process

There are countries like Spain, Greece and some areas of Italy that, due to large quantity production, cannot avoid, despite the move ahead the milling period year by year, to bring late the process season with late harvest deeply into winter time with olives at advanced stage of ripeness.
It is the case of large olive oil production quantity where the industrial criteria looking for efficiency with a constant attention to the ratio between extraction yield and optimal level of oil quality.

Figure 3 shows a schematic representation of example of trend of temperature starting from olives at 16°C harvested at advanced stage of ripeness during winter time and processed with traditional mill (red line). After crushing olive paste should goes immediately at 21°C. When we transfer the paste to the malaxer, a time of around 20-30 minutes should be necessary to heat until the settled temperature due to bad efficiency of malaxing technology used as heat exchanger.
The use of Thermal Conditioning Module for heating up immediately after crusher the olive paste from 21°C to 28°C (Figure 3, blue line) allows a more efficient malaxing. In fact, the immediate heating up of paste temperature after crushing gives the possibility to activate faster pectinolitic enzyme with a consequent fastest oil release into malaxer. Research demonstrate the possibility to reduce malaxing time until 50% keeping the same level of extraction yield with respect to the traditional technology. Moreover the investigation demonstrates that a reduction of malaxing time helps significantly reduction of loss of volatile compounds.
The use of Thermal Conditioning Module in case of late harvest helps the producers to keep high the ratio between yield and quality with, at the same time, a highest efficiency and consequent fastest processing time with respect to traditional systems.

The new Thermal Conditioning Module from Alfa Laval

Functioning of Thermal Conditioning Module is very simple. Olive oil paste coming from the crusher is pumped into the Thermal Conditioning Module, which utilizes flash thermal conditioning to instantaneously raise the paste to the temperature required. The conditioned paste is pumped directly from the Thermal Conditioning Module to a separate tank or a malaxer, where the mixing and final oil extraction take place.
The Module is designed for installation in the olive oil extraction process between the crusher and a holding/mixing tank. Module is preassembled and only requires an inlet connection for the paste from the crusher pump and an outlet connection to the mixing tank. Module is equipped with a hot or cold water storage tank and recirculation pump, making it easy to connect to any existing sources of hot or cold water present in the mill. A full wiring and control panel equipped with an easy-to-use touch screen are included.

by Giacomo Costagli
31 october 2015, Technical Area > Olive & Oil

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