Vol 117 (2004): Proceedings of the Florida State Horticultural Society
Handling & Processing

Early degreening research: establishing basic principles

Bill Grierson
Citrus Research and Education Center
Published December 1, 2004
  • citrus degreening,
  • packinghouse


On my arrival at the Citrus Experiment Station, Lake Alfred in July 1952, I was assigned a specific project, to find something better than ethylene, which "everybody knew" caused ugly fruit blemishes and horrendous decay. While apparently chasing this fantasy, I studied ethylene degreening. Ethylene was being used in incredible amounts, some packinghouses were weighing in several pounds of ethylene to start a room. Constant fear of losing ethylene led to sealed rooms with periodic ventilation schedules. A valuable clue to the amount of ethylene needed was that using kerosene fumes blown in from a "smokehouse" worked rather well. This was due, not to a magic component in the kerosene fumes, but to the large quantities of air blown into the rooms. Even without any analytical equipment it became apparent that very little ethylene was actually needed. Some basic principles became apparent. Adequate space MUST be left for air circulation. It is impossible to blow air through a stack of boxes. Airflow through stacks of fruit depends on establishing a slight pressure differential that will draw the air through. High humidity, just short of precipitation, was helpful, but hard to achieve. "Ethylene burn" was due to contaminants, usually fertilizer dust, on the fruit and boxes. Much peel injury blamed on degreening was due to the popular use of heated polisher brushes. That much established, some solid facts with regard to the fruit itself became apparent. 85 F was a sharp optimum for degreening oranges, but far less precise for grapefruit. Color change of Hamlin oranges ceased abruptly on leaving the degreening atmosphere, but Valencia oranges and Duncan grapefruit continued to degreen for up to 48 hours. Regreened areas on Valencia oranges were not "degreenable". Degreening could be impaired by ANY prior treatment, even manual handling. Payment of market claims for decay was costly. However, inappropriate accounting methods almost totally obscured other considerable financial losses due to poor degreening, thus providing little incentive for packers to spend money on needed improvement of degreening facilities.