I brewed a double IPA (Hopslam clone) with a predicted OG of 1.091. Despite double-crushing my grains and mashing for 60 minutes, my pre-boil gravity was only 1.051 and my OG after the boil and chill was only 1.060. I'm not too concerned, because it will be a great beer, but I'm wondering how I missed my numbers by so much. My pre-boil volume was 7.10 gallons and I had 6.25 gallons left after a 1 hour boil. My boil-off rate was much lower than normal, because I was using a condenser to capture the steam instead of a vent hood. Acc'd to Brewer's Friend, my brewhouse efficiency was less than 50%. Usually, I'm achieving total efficiencies of 65 - 75 percent. The only change I've made is the condenser. Any idea why I missed by OG by so much?