As a peach ripens, the part facing the sun gets a reddish blush and the part not exposed to sun (ground color) turns from green to yellow. The best way to tell if a peach is ripe is by looking for a yellow ground color.
Some varieties will have a slight green color to the background even when it is ready to pick. The peach will also have medium-soft flesh and will smell like a peach.
The peach on the right is ripe; the peach on the left is not. Notice the green color of the unripe peach. A peach will become round as it becomes ripe. An experienced picker can tell if a peach is ready by touch alone.
ally, fruits on the outside and top of a tree will ripen 5 to 10 days before the fruits in the middle and inside part of the tree. Also, different varieties of peaches ripen at different times. Early-ripening varieties may ripen weeks ahead of other varieties. Some varieties such as Redhaven require 4 to 5 harvests in order to pick the fruit at the best stage.
One method to determine fruit ripeness is to use a penetrometer to measure fruit softness. For peaches we use a hand-held gauge (example brand: McCormick) with a 8 millimeter diameter tip. Remove a 18 mm diameter piece of skin from the size of a peach with a blade. Slowly push the probe into the fruit until the guidemark is covered (about 10 mm) and record the pressure. Peaches for shipping are picked at 11 to 14 lb. Peaches at 7 to 10 lb are “well mature”. Fruit which reach 6 to 8 lb pressure are considered “ready to buy”. Fruit with 2 to 3 lb flesh firmness are considered “ready to eat”. (Adapted from the California Tree Fruit Agreement Program).
Peaches that are firmer than approximately 8 lb should not be refrigerated. Keep them at 50 F to 77 F until they soften below 8 lb and start to develop a peach aroma. At this point they can be refrigerated for several days.