By Adam Austing and Annie Klodd, UMN Extension Educators
Apple orchards have started their seasons as early-ripening varieties hit maturity. For homeowners with apple trees, perfectly timing the harvest of your apples can be trickier that one might expect.
Apple ripening will vary greatly by variety and even within the canopy of a single tree. Apple orchards use visual cues, sugar content, loss of starchiness, and flavor to decide when to harvest.
They also know the approximate time in the season when each variety is picked. For example, Honeycrisp is typically harvested in late September through October, while Zestar is harvested in late August or early September.
Many producers use visual cues to harvest fruit, particularly the change of the skin’s background color and over color. Background color for most apples is green, and this lightens to a yellow color (for example a yellow Post-It Note color) as the fruit matures. The over color (red, red striping, red blush, etc.) can mask the background color and may vary by environmental conditions such as hot weather, especially warm evenings, that prevent color development even though the flesh inside continues to mature.
Apples typically change in texture through ripening as well, but varieties like Honeycrisp maintain that firm texture through harvest and into storage.
Other attributes to consider for apple ripeness include preferred flavor and the development of sugars. If the apple tastes “starchy” or dry on the tongue it is not ripe yet. Apples have a high proportion of starch that is converted to sugar during ripening (both on and off the tree).
In large-scale apple production, this transition from starch to sugar is monitored using a starch-iodine test where they apply an iodine solution to the cut surface of several fruit. The starch stains purple and produces a pattern that is informative when compared to a standard index for the variety. However, this method is not recommended for small-scale production like home gardens.
Acidity can also be measured (pH or titratable acidity) as an indicator of maturity. However, the specialized equipment for monitoring this feature is beyond the scope for most backyard hobbyists.
Of course, taste testing should be part of the process when determining if your apples are ready for harvest. Keep in mind that our senses can play tricks on us. For example, high sugar can mask high acidity. High acidity can desensitize the tongue, making it difficult to assess later samples. And fresh fruit always seems to taste great right off the tree or vine, even if it is not actually at peak ripeness.