Adding DME to correct Pre-boil gravity didn't help me achieve my target OG

[TheBrewedPalate]

This past Sunday I brewed an Imperial Black Rye IPA (see Super Black IPA thread) and added too much hot water to raise my mash temp for mashout. So I decided to add some cold water to cool it down. However, I added too much cold water (took the mash temp from 179 to 155) and no matter how much hot water I added I couldn't get the temp up to 168. So after over an hour of extra mashing I collected the rest of my runnings and started the boil. When I took my preboil gravity I saw that I was short by 8 points and quickly went onto BeerSmith and calculated that I needed to add 1.11 lbs of DME to correct the gravity defieincy....

However, despite having corrected the pre-boil gravity I still fell short on by 8 to 12 points (discrepency between hydrometer and refractometer) after a 90 minute boil. This is the 2nd time this has happened (added DME and not achieving target OG)...

How can I prevent this from happening again?

 

[Trox]

Sounds your not boiling off as much as Beersmith thinks you are. I would boil about 5 gal. of water for 60 minutes, check to see how much you have left, then compare to what Beersmith thinks you should have left, and then enter the proper boil off rate into your equipment profile.