Five Keys to Successful Citrus Degreening

By Mark A. Ritenour

Many Florida citrus varieties reach legal maturity before developing the bright orange or yellow peel color consumers expect. As a result, fresh-market fruit often require degreening, a postharvest process that exposes harvested fruit to low concentrations of ethylene gas, a natural plant hormone that promotes chlorophyll breakdown and allows underlying yellow and orange carotenoid pigments to become visible.

It is important to remember that peel color and fruit maturity are not always the same. Citrus can be fully mature internally, with excellent juice quality and flavor, while still having a green peel. Peel color development is strongly influenced by environmental conditions, particularly cool night temperatures below about 55°F. In tropical regions where temperatures remain warm year-round, mature citrus often stays green despite being ready to eat. Conversely, fruit that have developed good orange color can partially regreen if left on the tree after warm spring temperatures return.

Because consumers often associate peel color with quality, successful degreening plays an important role in fresh-market citrus marketing. However, degreening primarily improves fruit appearance and generally does not improve internal eating quality. When properly managed, degreening can enhance marketability and consumer appeal. Poorly managed degreening, on the other hand, can increase decay, accelerate deterioration and reduce packout quality.

Following are five keys to successful citrus degreening.

1. MAINTAIN PROPER TEMPERATURE

Temperature is one of the most important factors affecting degreening success.

Target temperature:

• 82-85°F: Best for rapid commercial degreening and chlorophyll removal
• 68-77°F: May promote enhanced carotenoid development and deeper orange-red coloration in some mandarin-type citrus, although treatment times are longer.

Avoid:

• Temperatures above 85°F, which can slow degreening while increasing respiration and fruit deterioration
• Excessively low temperatures, which lengthen the time required to achieve acceptable color

2. DON’T OVERUSE ETHYLENE

More ethylene does not necessarily mean faster or better degreening. The recommended concentration is 3 to 5 parts per million ethylene. Higher concentrations generally provide little additional benefit and increase decay pressure. Accurate metering and periodic monitoring help maintain effective concentration while minimizing unnecessary costs.

3. MAINTAIN HIGH RELATIVE HUMIDITY

Because degreening occurs under relatively warm conditions, humidity management is essential. The recommended relative humidity is 90% to 95%.

Benefits include:

• Reduced fruit and peel water loss and shriveling
• Better maintenance of fruit firmness
• Improved appearance and packout quality

Avoid conditions that allow free moisture to accumulate on fruit surfaces, as this encourages decay development and slows degreening. Cardboard containers may require somewhat lower humidity to prevent carton weakening.

4. VENTILATE TO PREVENT CARBON DIOXIDE BUILDUP

Fresh citrus fruit remain alive after harvest and continue to respire, consuming oxygen and releasing carbon dioxide (CO₂). Carbon dioxide and ethylene act antagonistically. Even relatively low CO₂ concentrations approaching 0.1% can significantly reduce color development.

The recommended ventilation is approximately one complete air exchange per hour based on room volume. Continuous ventilation is generally preferable to periodically opening room doors because it maintains more stable temperature, humidity and ethylene concentrations.

5. ENSURE ADEQUATE AIR CIRCULATION

Uniform airflow helps maintain consistent conditions, especially temperature, throughout the degreening room. Recommended airflow is a minimum 10 cubic feet per minute per field box. Poor airflow often results in uneven color development and inconsistent fruit quality.

CULTIVAR DIFFERENCES MATTER

Not all citrus cultivars respond equally to degreening. Some varieties degreen readily, while others develop desirable peel color more slowly, particularly in Central and South Florida production regions. Small-scale evaluations can help determine the most effective degreening strategy for new cultivars before commercial implementation.

TAKE-HOME MESSAGE

Successful citrus degreening depends on managing temperature, ethylene, humidity, ventilation and airflow as an integrated system. Maintaining recommended conditions improves peel coloration, minimizes decay and water loss, and maximizes fresh-market quality. While 82 to 85°F remains the standard for rapid commercial degreening, some cultivars may develop superior coloration under cooler conditions when longer treatment times are practical.

Mark A. Ritenour is a professor at the University of Florida Institute of Food and Agricultural Sciences Indian River Research and Education Center in Fort Pierce.