Internal browning is a low-temperature storage disorder of certain apple cultivars which develops in some fruit stored at or just below freezing. A cross section of an apple typically shows affected tissues to be brown and firm and usually radiating out from the core. Occasionally, the browning may be confined only to the core or the core area can be normal and browning is in the outer layers. Firm fruit allows the diagnosis of internal browning from the other internal physiological disorders. Putting apple fruit promptly into storage of apples at 38° to 40 °F combined with controlled-atmosphere storage will control internal browning.
To read about which cultivars and growing conditions enhance the liklihood of internal browning, Washington State University has a good fact sheet found at: