Olives deteriorate during the storage time between harvesting and processing, a problem that harms the quality of the oil extracted from them. Therefore, it’s important to find ways to store the fruit for longer periods that won’t adversely affect it.

Researchers tested the effects of moderate freezer-storage on olives and found the quality of the olive oil derived from them is comparable to the quality of oil derived from non-frozen fruit.
See more: How Cold Temperatures Can Help Olive Production
The caliber of extra virgin olive oil is dependent upon the composition of the fruit at the time of processing. Several factors are essential for producing the highest grade of oil:

  • harvesting at the optimum stage
  • a short time between harvesting and milling
  • superior oil extraction procedures
  • the best storage conditions

Of these, the time interval between harvesting and milling is especially critical. When the capacity of the olive milling plants can’t keep pace with the volume of olives, the fruit is stored at the temperature of the surrounding environment for several weeks prior to processing.

Such storage can result in an array of harmful effects. These include the following:

  • fermentation
  • growth of bacteria and fungi
  • increased acidity
  • decreased stability
  • musty scent
  • decline in pigment

Consequently, extra refining of the oil is necessary, which increases production costs.

Prior research had shown that freezing olives at -18°C for 24 hours reduced the nutrient profile and stability of the oil extracted from them. In an attempt to discover a solution to the storage problem, the new study, conducted in Iran, tested the effects of freezing olives at moderate temperatures of -4°C. The scientists also endeavored to determine if one cultivar of olives responds better to freezing than another.

The cultivars Mission, Koroneiki and Arbequina were chosen because they are commonly used in Iran. After harvesting, a control group of olives was immediately processed into oil, while other groups were stored at -4°C for one week and three weeks before processing. The oil from all groups was assessed for peroxide value as well as the content of fatty acids and the pigments of chlorophyll and carotenoids.

Analysis of the results showed the oil extracted from the olives frozen at a moderate temperature had the same characteristics of the oil extracted from the control group. Freezing didn’t reduce the content of beneficial nutrients. Moreover, no differences were noted between cultivars.

The authors concluded that freezing could be a viable means of preserving olives during the period between harvesting and processing. They noted that conducting the same study on more cultivars and performing a broader spectrum of tests on the extracted oil may be worthwhile.

However, the positive findings led them to believe that olives could be harvested at the optimal time and safely stored at moderate frozen temperatures while being shipped to mill plants. Upon arrival at this destination, the olives could remain frozen until plant workers were ready to begin the oil extraction process. The study was published in the journal Advances in Horticultural Science.

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