As you know I have only started BIAB Yesterday I did one of Trialbens S & W Summer Ale. My preboil was 1.030 but after the boil it had only risen 4 points. 1.034. The recipe suggested 1.048 so you can see I was a long way off. What causes this. Is it a not vigorous enough boil. It was rolling although I admit it may not been enough.I may have to get a more ferocius flame. Any help welcomed.