9Olive handling, storageand transportationPrimo ProiettiDepartment of Agricultural, Foods and Environmental Sciences,University of Perugia, Perugia, Italy
Abstract
Avoiding mechanical damage and controlling time-temperature relationships arekey factors for satisfactorily handling and storing olives during the period fromharvesting to milling. A ten-point list of handling and storage practices is proposedas well as a semi-log diagram for the choice of suitable time-temperature relation-ship. The criteria for optimizing the harvesting-milling link are discussed.
9.1 The autocatalytic nature of olives and oil degradation
The handling and storage of olives in the period between harvesting and millingis critical for oil quality. Improper conditions may trigger a chain of degradingreactions whose autocatalytic mechanism is such that degradation increases at anaccelerated pace. In fact, some products of oil degradation such as monoglyceridesand peroxides become the catalysts for further degrading reactions. Figure 9.1 showsa flow-chart of olive degradation and its effect on oil quality.
The two critical conditions for satisfactory olive handling and storage beforemilling are:
• avoid mechanical damage to the olives, and
• control the time-temperature relationship.
9.2 Avoid mechanical damage to the olives
Crushing and bruising of olives cause cellular structures to break and hence mixingof the oil, which is originally stored in vesicles (cell organelles called spherosomes)
The Extra-Virgin Olive Oil Handbook, First Edition. Edited by Claudio Peri.© 2014 John Wiley & Sons, Ltd. Published 2014 by John Wiley & Sons, Ltd.
108 CH09 OLIVE HANDLING, STORAGE AND TRANSPORTATION
OLIVES
Breaking andbruising
Microbialgrowth andfermentationby:
- bacteria- yeasts- moulds
Cell enzymesand air comeinto contactwith the oil
Pest attack
Sensory defects:‘winey-
vinegary’,‘fusty’,‘musty’
Lipolytic andoxidativeenzymes
Lipolysis Lipid oxidation
Free fatty acidsMonoglyceridesand diglycerides
Hydroperoxides
Increase in freeacidity
Increase inperoxide andK232 value
Sensory defect:‘rancid’
Mechanicalinjury, soiling
Spoilage reaction
Degradation effects
Catalytic effects leading tospoilage
Figure 9.1 The mechanisms of olive spoilage and oil degradation.
9.3 CONTROL THE TIME-TEMPERATURE RELATIONSHIP 109
with other cellular components, especially hydrolysing and oxidizing enzymes. Inthese conditions, in the presence of oxygen from the air, oil degradation readilystarts. Due to the presence of sugars in the cellular juice, bacterial and yeast fermen-tation may also take place with formation of ethanol, acetic acid and ethyl-acetatecausing the ‘winey/vinegary’ sensory defect.
Fermentation is an exothermic phenomenon, so it also causes an increase intemperature, which further favours microbial growth and fermentation. The overallresult of olive fermentation and heating is the so-called ‘fusty’ defect.
When storage under improper conditions goes on for days, mould growth, gener-ally Penicillium and Aspergillus species, causes a massive production of degradingenzymes and the appearance of the ‘musty’, ‘humid’, ‘earthy’ sensory defects.
For oil transportation and storage, rigid plastic containers should be used(15–20 kg crates or 200–300 kg bins) with olives in layers not thicker than 30 cm.Thick layers cause crushing of the olives in the bottom layers. Crates and bins forolive transportation and storage must have ventilation holes and should be equippedwith a foothold for the overlay, to allow good air circulation (Figure 9.2). Trucksfor olive transportation in bulk with mechanical or hydraulic discharge can be usedonly if the period of time from harvesting to milling is a matter of very few hoursFigure 9.3.
Strictly avoid putting the olives on the floor or in sacks.
120 cm120 cm
30 cm 50 cm
(a) (b)
Figure 9.2 Plastic containers for olive handling, storage and transportation: (a) 200–300 kg binto be handled by forklift trucks. (b) 15–20 kg crates for manual handling.
9.3 Control the time-temperature relationship
In general, as a rough estimate, we may say that the rate of degradation reactionsincreases with temperature according to an exponential relationship, while theoverall degradation effect is proportional to time. A frequent way to represent
110 CH09 OLIVE HANDLING, STORAGE AND TRANSPORTATION
Figure 9.3 Truck for olive transportation in bulk with mechanical or hydraulic discharge at themill’s discharge hopper.
time/temperature relationships of technological operations is in a semi-logarithmicgraph, with temperature on the abscissa in a linear scale and time on the ordinatein a logarithmic scale. In such a plot, time-temperature conditions that determineequal degrading effects are represented by oblique lines. Figure 9.4 shows the
100
10
1
0 10 20 30Temperature, °C
Tim
e, h
Standard orsuggestedconditions
Suitableconditions
Unsuitableconditions
Figure 9.4 Time-temperature relationship of olive-storage conditions in the period fromharvesting to milling. Source: Peri, C. (2013). Reproduced with permission from Wiley.
9.3 CONTROL THE TIME-TEMPERATURE RELATIONSHIP 111
time-temperature relationship of the storage of healthy olives. The graph is theresult of five years of field tests carried out by Association 3E for the production ofsuper-premium olive oils (Peri et al. 2010; Peri 2013).
The temperature scale varies from zero to 30 ∘C, while the time scale varies from1 to 100 hours. The two oblique lines represent the border area for satisfactory olivestorage. They divide the diagram into two parts: the time-temperature conditions inthe lower area are suitable, while those in the upper area are unsuitable for goodolive storage. Between the two lines, standard conditions can vary in relation to thecultivar and the degree of maturity of the olives.
It can be seen, for example, that it is advisable not to exceed a holding time of1 h at temperatures of 29–30 ∘C, while at 5–7 ∘C, storability can be extended up to4 days. At 15 ∘C the olives can be safely stored up to about 20 h and at 10 ∘C up to50 hours.
In order to meet the recommended conditions of olive handling and storage, thedecalogue in the box should be considered.
Postharvest handling and storage of olives
1. Closely control temperature according to Figure 9.4.
2. Avoid olive breaking and bruising during harvesting by usingappropriate harvesting machines and mechanical facilitators (seeChapter 8).
3. Avoid contact between olives and soil in order to avoid microbialcontamination, especially moulds.
4. Avoid mixing good and healthy olives with broken or mouldyones.
5. Avoid mixing fly-infested olives with healthy ones. The flies’ larvae area super-effective dispenser of degrading enzymes and micro-organismsin the olive pulp.
6. For olive transportation and storage use rigid plastic containers withventilation holes and layers of olives not thicker than 30 cm.
7. Avoid exposure of harvested olives to the sun or rain. Rain on storedolives not only favours microbial growth but also acts to inoculate andpropagate micro-organisms. Storage at the grove or at the mill shouldtherefore not be in the open air but in a covered, well-ventilated space.Relative humidity in the storage environment should not exceed80%.
8. All the above points become more critical as olives ripen because themechanical resistance of the olive skin and pulp decreases.
112 CH09 OLIVE HANDLING, STORAGE AND TRANSPORTATION
9. A critical control step at the mill reception area should be visualevaluation of the integrity of the olives so that mixing of good and badolives is carefully avoided.
10. The olive storage area should be clean and free of atmosphericcontaminants especially solvent vapours, smoke, exhaust, fusty smell,and so forth.
9.4 Management of the harvesting-milling link
It is often recommended that olives be milled ‘in the shortest time possible’ afterharvesting. This is scientifically inaccurate because the time-temperature relation-ship, as presented in Figure 9.4, is not taken into consideration. It is also misleadingin process management terms as it frequently leads to irrational procedures if appliedin a rigid or too restrictive way.
The problem that arises is that of rationalization of the harvesting-milling link.Trying to mill the olives immediately after harvesting creates a rigid connectionbetween the harvesting operation and that of milling, with the consequence of orga-nizational inconsistencies and diseconomies of scale. Micro-mills with a very lowhourly working capacity are becoming common. They operate in direct connectionwith the harvesting by adapting the rate of milling to the rate of harvesting. Thelabour costs are high and it becomes impossible to carry out the milling processunder steady, well-controlled conditions.
Instead, if the olives are handled and stored under proper conditions until suit-ably sized batches are obtained, they can be milled in a short time in larger-sizedmills, in standardized conditions and with more reliable qualitative and quantitativeresults. Optimizing this step of olive handling and storing before milling is criticalfor optimal sizing of the mills.
References
Peri, C., Kicenik Devarenne, A. and Pinton, S. (2010) 3E Super-Premium selectionfor extra-virgin olive oil. Beyond Extra-Virgin, The Fourth International Confer-ence on Olive Oil Excellence, organized by Association 3E (Milan, Italy), theAcademy of Georgofili (Florence, Italy), The Culinary Institute of America (StHelena, California) and the Olive Center of the University of California Davis,Verona, 22 September 2010.
Peri, C. (2013) Quality excellence in extra-virgin olive oil, in Olive Oil Sensory Sci-ence (eds E. Monteleone and S. Langstaff), John Wiley & Sons, Ltd, Chichester.
