Gordon Johnson, Retired Extension Specialist; gcjohn@udel.edu
I was asked earlier this year what could cause peaches not to ripen properly after harvest. Peaches will ripen off the tree if harvested when the background color has changed from green to yellow in yellow peaches or from green to white in white peaches. Other signs of ripening are a reduction in density, increase in size, increase in red color in some varieties, increase in soluble solids (sugars), and decrease in organic acids.
If a peach is picked too early (green) it will not ripen properly. Other factors that could affect ripening would be a loss of leaves due to diseases such as bacterial spot; certain fruit diseases such as bacterial spot, rusty spot, or scab: damage to limbs from heavy fruit loads or storms; drought stress; soil waterlogging; excessive fruit loads; or excess shading of fruit.
Another major factor affecting fruit ripening and quality is storage temperature. Peaches, plums, cherries, and apricots are susceptible to chilling injury when fruit are held at temperatures in the range of 36 to 50°F. This is often known as the “danger zone”. The flesh can become translucent, turn brown, lose flavor, bleed, turn leathery or become mealy. These symptom occur when customers put the fruit out to ripen at room temperature.
To prevent this injury, store stone fruit colder at temperatures in the range of 29 to 34°F. It is also advised to precondition peaches before they go into cold storage by storing at 68 F for 1 to 2 days after picking but prior to cold storage at 32°F. Peaches taken out of cold storage should also be held at 68 F for 1-2 days before sales.
For short term storage, keep stone fruit at temperatures above 50 F to avoid quality problems and avoid the danger zone temperatures.
Symptoms of flesh browning and mealiness in peaches as a result of chilling injury.
Parts of this article were adapted from Keeping it Cool: Cold Storage Recommendations for Apples and Peaches and Determining Peach Fruit Maturity from the University of Maryland and Cold Storage Conditions: Harvest & Storage of Maine Tree Fruits from the University of Maine.