Bitter pit. Photo courtesy of Penn State University.
What you see: Little, dark sunken spots on the outside of your apple; and/or brown spots just underneath the skin
What it is: Bitter pit, a defect caused by insufficient calcium
Eat or toss: Peel off the spots and eat! This is a physical disorder caused by a nutritional problem in the orchard. It’s not harmful.
If you’re an apple grower, bitter pit is a bitter pill.
It’s ugly, manifesting as sunken spots on the outside of the apple, and spots just below the skin.
The culprit is generally believed to be a calcium deficiency. Calcium is important to cell wall development, and calcium concentration in the fruit decreases as you move from the core to the skin. Without enough calcium, some cells just under the apple’s skin die and eventually shrivel, creating that pitted look.
Fortunately for you, dear apple eater, the disorder usually only affects the top millimeter or so of the apple. So, peel it off and you'll never know the difference.
Bigger apples more at risk
Fascinatingly, the disorder can be brought on by excessive fertilization—too much nitrogen provides so much growing power that the calcium is diluted. Large apples are more at risk for bitter pit because their calcium stores are spread thin. Temperature and humidity play a role too. Because calcium is transported to the fruit for only part of the growing season, a late influx of water might cause a growth spurt in the apple, without the accompanying supply of more calcium.
Bitter pit is particularly frustrating for growers because its presence isn’t obvious during harvest. In fact, it can lurk invisibly for three or four months in cold storage (apples keep well and are commonly stored for months). During that time, something happens within the apple that sets the stage. Once a smooth-skinned, but afflicted apple leaves its long term storage and spends a few days at room temperature, the bitter pit appears.
Research ongoing to predict bitter pit
Because bitter pit is a only a physical issue (and not something containing a potential pathogen), a freshly harvested apple with the condition will still be an attractive, healthy, tasty snack. So, growers want to sell them right away, and not keep them in storage.
The problem is that at harvest time there are no visual clues identifying which apples are affected and which aren’t. Farmers have to guess and guessing wrong leads to waste.
So, how do you know if a harvest is affected with bitter pit if the visible markers don’t show up for months? Researchers are working on several means of testing. Pomologist Rich Marini and his team at Penn State University recently developed a test for Honeycrisp apples, which are particularly vulnerable to bitter pit. The test, which is currently undergoing review to verify its effectiveness, analyzes dried apple peels for calcium and can help predict the disorder, and help growers prioritize which fruit to sell at harvest and which to store for later.
Rich Marini - Professor of Horticulture. Penn State University.
Research yields test to predict bitter pit disorder in Honeycrisp apples. Penn State News. Pennsylvania State University.
Apple Fruit Disorders - Crop Load and Nutrient Management to Prevent Bitter Pit. Penn State Extension. Pennsylvania State University.
Bitter Pit Control in Apples. Ministry of Agriculture, Food and Rural Affairs. Ontario.
Market Diseases of Apples, Pears, and Quinces. Bitter Pit . Washington State University. Tree Fruit Research and Extension Center. Post Harvest Information Network.