Hit pre-boil SG right on, but real low on SG before adding yeast?

What would be some reasons to hit pre-boil FG fine (All Grain), but end up low (like 6-7 points) on your SG before adding yeast? I'm trying to think of all the things that could cause this to pinpoint a problem I've had on the past 2 beers.

- Didn't loose enough in evaporation.
- Boil over (which did happen on one of the two beers)
- Not having the burner up higher? I keep it at a sweet spot so its boiling good but not to the point where it starts building up and I have to stir it every 1-2minute to stop a boil over. I used to do that but figured I was wasting propane.

Sounds like you didn't boil off enough. A half gallon to much beer more than you anticipated can easily lower your OG by 5 points...... Either turn up the heat or better yet, collect less from your MLT next time.

Or boil longer...

Some say that if you don't stir well, you can get incorrect OG readings. I take my OG readings after pitching the yeast and doing my shake & stir routine.

+1 on not boiling off enough. Pre-boil & post-boil gravity is where a refractometer is your best friend.

It could be you're not boiling it hard enough. For the first half you can boil lightly, but the last half of the boil you want a nice rolling boil. Both for evap and to drive off all the nasty nasties.

B

and make sure you're correcting the temp for your hydrometer! but more than likely it's not boiled enough.

Yea you guys are right, its probably like .25-.5g extra of wort... which is why I'm getting a lower SG. I need to get a refractometer and take wort measurements throughout the boil so I can track that better. Its like the only part of the process I'm not confident in keeping consistent yet.

I've found it's easier to err on the low side when making your preboil measurements. Boiling longer messes up my hop schedule. If my knotch on my spoon shows I'm a quart low at the end of my boil....I simply add a bottle of spring water. Hit the OG, spot on.