Fresh olives are highly sensitive to storage temperature and atmospheric composition before processing. While cold storage is commonly used to slow respiration and delay deterioration, inappropriate temperature or gas conditions can trigger serious physiological and physical disorders. Among these, chilling injury, carbon dioxide injury, and nailhead disorder are the most significant causes of quality loss in stored olives.

Research has shown that elevated carbon dioxide (CO₂) levels, particularly when combined with extended storage duration, substantially increase the severity of chilling-related damage. Understanding the interaction between temperature, storage time, cultivar sensitivity, and atmospheric composition is essential for growers and processors seeking to protect fruit quality prior to processing.

Physiological And Physical Disorders In Stored Olives

Chilling injury (CI)

Chilling injury is one of the most damaging postharvest physiological disorders affecting fresh olives stored before processing. It develops when olives are exposed to temperatures below their tolerance threshold for prolonged periods.

Chilling injury can become a major cause of deterioration under the following conditions:

• More than 2 weeks at 0°C (32°F) 
•  More than 5 weeks at 2°C (36°F) 
•  More than 6 weeks at 3°C (38°F)

The disorder initially develops internally, making early detection difficult. Internal browning begins in the flesh surrounding the pit and progressively radiates outward toward the skin as storage time increases. When skin browning becomes visible, the injury is already advanced and typically associated with severe quality loss.

Cultivar susceptibility plays a critical role. The established order of sensitivity to chilling injury is Sevillano (most susceptible), followed by Ascolano, Manzanillo, and Mission (least susceptible).

Nailhead disorder

Nailhead is a physical storage disorder characterised by surface pitting and spotting of the olive skin. It results from the death and collapse of epidermal cells, creating air pockets beneath the fruit surface. These air pockets cause the characteristic pitted or hammered appearance.

Nailhead typically develops under moderate cold storage rather than extreme chilling, with symptoms observed when olives are stored at 10°C (50°F) for six weeks or longer, or at 7.5°C (45.5°F) for twelve weeks or longer.

Although nailhead does not always involve internal browning, it significantly reduces visual quality and marketability and may increase susceptibility to secondary decay during extended storage.

Carbon dioxide injury

Carbon dioxide injury occurs when olives are exposed to CO₂ concentrations greater than 5% for extended periods. This disorder often overlaps with chilling injury and significantly intensifies tissue damage.

Symptoms of carbon dioxide injury include internal browning similar to chilling injury, increased incidence and severity of decay, and accelerated loss of firmness and fruit integrity.

Elevated CO₂ disrupts normal respiratory metabolism, leading to cellular damage and increased vulnerability to physiological failure. While controlled atmospheres can be beneficial under carefully managed conditions, excessive CO₂ consistently results in poorer storage outcomes.

Controlled atmosphere comparison 

Controlled atmospheres using reduced oxygen and moderate carbon dioxide levels help maintain firmness and green skin colour when storage temperatures are kept above 5°C.

Interaction Between Temperature And Atmospheric Composition

The interaction between storage temperature and atmospheric composition is critical in determining olive storage success. Elevated CO₂ levels intensify chilling injury even at temperatures that might otherwise be considered safe.

By contrast, controlled atmospheres containing approximately 2% oxygen combined with up to 5% carbon dioxide have been shown to maintain flesh firmness and preserve green skin colour when olives are stored at 5°C (41°F) or higher.

This highlights the importance of managing storage conditions as an integrated system rather than relying on temperature control alone.

Practical Implications For Growers And Processors

Physiological and physical storage disorders can result in substantial economic losses through reduced yield, downgraded quality, and increased waste. These risks are particularly pronounced during seasons of high production when fruit must be held before processing.

Key strategies to minimise postharvest losses include avoiding storage temperatures below 5°C, limiting exposure to CO₂ concentrations above 5%, reducing storage duration wherever possible, and accounting for cultivar-specific sensitivity when planning harvest and storage logistics.

Conclusion

CO₂ chilling injury and related physiological disorders represent a significant challenge in fresh olive storage. The combined effects of low temperature, extended storage duration, elevated carbon dioxide levels, and cultivar susceptibility determine the severity of damage.

By maintaining appropriate temperature ranges, managing atmospheric composition carefully, and tailoring storage practices to cultivar characteristics, growers and processors can significantly reduce postharvest losses and maintain olive quality before processing.

References

Postharvest Technology Center, University of California, Davis