I've got a couple of kegs in the kegerator that have been under pressure for about 10 days. One is a cider that is a bit too dry and the other is way too sweet. If I mix them 80/20 or so it's pretty good. They are both pressurized at 12 psi at about 38 degrees. The problem is the very sweet cider comes out all foam and the dry cider comes out practically flat. Once the sweet cider defoams it's flat too. Why is the dry cider so flat?