This has been happening to me over the last few brews... at first I thought it was a fluke mis-calc with the hydrometer, but now I beginning to wonder. Before boiling, I have 352.93 gravity points. After boiling, I get 282.75. the pre-boil points represent an efficiency of 91%, while after boil represents 73%. (all temperature corrections have been applied) Has anyone experienced this kind of loss? I've heard the browning reaction to some sugars in long boils (90 minutes) can cause a loss of points, but I can't believe it would be that much. I have the same loss with 60 minute boils as well.