Hi everyone, I have done a few brews now and accepted that the efficiency with my equipment is around 58-65 or so. What I have been baffled with is I usually hit my est. pre-boil OG, but my post boil is 3-7 points off on the low side. What could cause this? I do BIAB, one vessel mash and boil. Water levels post boil is spot on, even lower sometimes. Used a refractometer and hydrometer to confirm and they both show about the same gravity values. Fairly new to the hobby and loving it. Thanks for any suggestions..