Overshot sg, og was low, volumes were spot on?

[JeffLacoy]

Did a pale ale at the crack of dawn today. Predicted sg was 1.040, managed to hit my preboil volume and came up with 1.042. Boiled for an hour, again, volume after boil was right on the money, transferred, cooled, took a gravity this afternoon, only made it to 1.049?

Just confused, and curious as to what I might look at for causes. First time using RO water and adjusting my minerals and ph, but that shouldn't be an issue.

 

[McKnuckle]

Use a dilution/boil-off calculator (such as the one by Brewer's Friend) to determine what your pre-boil gravity really was, given your pre- and post-boil volumes and OG. Pre-boil gravity is notoriously finicky to accurately measure.

 

[JeffLacoy]

If I'm using this in reverse correctly, I had 7.6g preboil, and ended with about 6.25g. With an og of 1.049, says my preboil should have been 1.040. Seems a bit more reasonable to me. Just disappointing is all!

 

[MagicMatt]

Predicted sg was 1.040, managed to hit my preboil volume and came up with 1.042.

You say "predicted sg" - what exactly are you referring to? If you mean a predicted OG of 1.040 and your preboil gravity was 1.042, then that means you got way more conversion efficiency out of the mash than intended if your volumes were indeed accurate.

If by "predicted sg" you mean your pre-boil gravity, then 1.042 is not far off - you were slightly more efficient than predicted. Next time up the efficiency percentage in whatever calculator you are using (say from 70% to 73%) to start, and see if that doesn't yield more accurate results.

But in general yes, I've found that an hour long boil will usually increase the gravity by 8-12 points.