I pick blueberries every year and have never run into this problem. This year the skin area on the underside of the blueberry is very tough. So bad that you have to pull it out of your mouth when you are eating it. Not all the blueberries are like that but I'd say at least half. This is very disappointing due to I pick enough to freeze and use all year. I've done a search and cannot find anything that makes reference to this. Just wondering if anyone else has noticed this and if you know what causes it.