A: I was able to locate two universities (Washington State and University of California) which have conducted studies of various types of apples. Both universities have discovered the potential cause most likely occurs after harvesting of the apples. I am sure there are other universities conducting the same research, but these two directly addressed the internal discoloring of the flesh around the core of the apple. The internal browning of apples during postharvest storage varies from year to year, but there is strong evidence pointing to how early the apples are harvested and the carbon dioxide concentration in storage atmospheres. The occurrence of internal browning was reduced when the apples were harvested within 180 days after bloom. If left on the tree longer, the potential for internal browning increased. In addition to harvesting at the appropriate time the apples needed to be stored where the concentration of CO2 was at levels below 0.5% to reduce losses from the internal browning disorder. The good news is the cause is not a pathogen such as a fungi, virus or bacteria and in most instances this problem can be avoided by proper harvesting and storage procedures. Unfortunately, you and I cannot detect this problem simply by looking at the external part of the apple – it is just the luck of the draw.