Monitoring Peach and Nectarine Ripening
Bill Shane, Tree Fruit Specialist
Michigan State University Extension
Guidelines are presented here to help Michigan growers, packers, shippers, and marketers deliver high quality peaches and nectarines. Fruit firmness, fruit size, shape, and skin color are key factors. Generally, the ripening sequence of a typical peach fruit on the tree is: 1) rounding/filling out of peach, 2) change of background color changes from green to yellow (or white if a white flesh type) along with a drop of firmness, 3) increase of peach aroma.
Once a peach or nectarine is picked, the sugar content does not increase. Fruit left on the tree will generally continue to develop sugar and reduce flesh acidity. Fruit picked late will have poorer storage characteristics. Judging the correct harvest time is complicated. A trained picker will use her/his hand to feel for a rounded suture, sufficient size, and adequate background color development.
A key tool for monitoring peach ripening is a penetrometer for measuring fruit firmness. Although experience is needed to learn the ripening characteristics of each peach type, firmness monitoring provides an objective tool to help determine the extent and speed of ripening, and to communicate with wholesale buyers and sellers. A penetrometer (also called a pressure tester), commonly used by the apple industry to test apple firmness, can be used to plan peach harvesting and storage. Common brands in use by growers are the Fruit Testers, McCormick, Effegi, and Magness-Taylor pressure instruments.
Test peach fruit using a penetrometer with an 8-millimeter diameter tip (5/16” pear tip). This is the smaller of the two tips provided with several standard penetrometers available from orchard supply companies. The part usually sampled is the cheek, however, the first region to become soft may be the shoulder, tip, or suture, depending on the variety and year. Fruit should be at about room temperature when tested because cold fruit can give higher readings. Remove a dime to quarter-sized slice of peel from the fruit, and then use sufficient uniform force to submerge the tip to the guide mark in approximately 2 seconds. Better readings are obtained if the fruit is held against a non-moving surface—a drill press stand works very well.
Peach firmness guidelines
(if firmness is above 8 lb: keep fruit above or below 36-460 F to avoid temperature-induced mealiness)
12 to 14 lb: picking for long distance wholesale market
8 to 12 lb: soft enough for transport to retail stores
(firmness below 8 lb: less susceptible to temperature-induced mealiness)
6 to 8 lb: arrive at final market
2 to 3 lb: should be purchased by end consumer
credit: This summary is based in part on work and summaries developed by Dr. Carlos Crisosto, Kearney Agricultural Center of the University of California.