Freezing Olives After Harvest Doesn't Affect Olive Oil Quality

Scientists found a possible solution to the reduction in quality that comes from storing olives at ambient temperatures -- storage at moderate freezer temperatures.

Nov. 10, 2017
By Mary West

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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 Also: 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. 

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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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