I have not had the problem so far but I recall the orchard I worked at many years ago would use calcium nitrate as a foliar feeding when we sprayed pesticide. Not always but a few times in summer as the apples grew to hopefully avoid the issues of water core, internal cork ect that are related to shortages of calcium as the fruit developed. I believe this product is still available as I have seen ads for it in fruit growing magazines.

I have noticed some commercial orchards around here have issues with some varieties having water core and other varieties next to it not having an issue. Certain apple varieties definitely seem more susceptible to having issues with the fruit not getting enough calcium. In this example, the orchardist had golden delicious (4 rows) and no problem. The next 4 rows were red delicious. The fruit looked great but every year 90% of the fruit had water core. The next 4 rows were jonathan and no issues. He finally cut down the red delicious as worthless except for blending into apple cider.

Did your brown flesh spotting occur on many varieties or just one of your varieties?

spartan apples; thx for reply. Not sure what variety; I have over dozen and only noticed the suspected calcium deficiency when peeling and coring for apple chips. It was definitely not all varieties. The same apples also had some mushiness around the core which looks like "water core" pics on google. I'll pay more attention next year; it was a very small problem this year showing up only very infrequently. Again, thx for advice. Mark in MN

Could be bitter pit which results from lack of sufficient calcium in the cells. Most often results from a water shortage, even tho brief & erratic. Some apples are more susceptible than others.

Mulch the trees.out to the dripline and ensure adequate water through the growing season.

Foliar Calcium either:

Cal 175

Stop-pit

Calcium Chloride Flakes