Written by Rhoda Burrows, former Professor & SDSU Extension Horticulture Specialist.
Do you know how to tell when an apple is ready to pick? Color change can be deceiving, since some apples turn red before they are fully ripe. Apples develop flavor and sweetness over time, and sometimes the best test is simply to keep sampling the fruit until it has developed its full flavor.
Another indicator is to slice open a few apples, and check the seed. The seed will turn brown when the apple is ripe. One clue can be that green areas (for example, around the blossom end) on the apple turn yellow, a useful indicator for those varieties in which the fruit don’t all ripen at the same rate.
Over-ripe apples can develop “water-core”, which shows up as a water-soaked ring of tissue in the flesh (see photo). Apples with water-core will be very sweet, but will not keep long, so they should be used as soon as possible. They are perfectly safe to eat.
I often hear people say that some apple varieties should not be picked until after a light frost, as this is required for ripening. While it is true that a light frost (around 30° F) will cause an increase in ethylene (the natural ripening compound) in the fruit so that the ripening is hastened, all apples can ripen fully without a frost.
What about a hard freeze (below 28° F)? If one is predicted, and the apples are nearly ripe, it is probably better to go ahead and harvest the apples, and let them finish ripening in storage. (Just don’t store them anywhere where they will be subjected to the same freezing temperature!) However, if the apples do get frozen on the tree before harvest, don’t touch the fruit until they are fully thawed. Frozen fruit will have a hard glossy appearance and may have a purplish tinge. If the cold temperature was for only a few hours one night, the fruit is likely to recover. With longer time periods or repeated exposures, the fruit will sustain more damage, and even if it looks ok, it will not keep well and should be used or processed as soon as possible.
Apples will keep best when stored at 32-34° F; they will freeze at 29° F. Try not to store them with carrots, as the ethylene from the apples will be detrimental to the taste of the carrots.
