Just wondering how there could only be an eight point change in gravity from mash to post boil. Any thoughts?
it amounts to about 10 % boil off. maybe a bit short but… if it seems wildly off I would check your instruments!
Hmmm . . . failure to adjust for temp? Weaker than expected boil? Shorter than expected boil due to daylight savings?
I boiled the wort (vigorously) for 75 minutes… I lost at least 1 1/2 gallons of water in the boil during that time. And I waited until the liquid for both was around 70F. Is 10% boil off average or close to average? I’m just used to seeing a bigger difference… maybe twice what I got on this brew. RDWHHB, right?
Was it an 11 gallon batch? I never brew batches that big, but 1.5 gallons of water lost in a 75 minutes boil doesn’t seem like a lot for a batch that big, maybe you did need a more vigorous boil. That being said, 1.067 isn’t that bad, so yeah, RDWHAHB
for sure RDWHAHB but also check your instruments cause that math doesn’t work out unless it was a 10 or 11 gallon batch.
if it’s a 5 gallon batch that’s 20% boil off and you should have ended up with 1.082 ish on a 10 gallon 1.5 gallons is ~9% which would be around 1.070
boiled 8 gallons down to just over 6 gallons… the hops soaked up a good bit too. i was really expecting a higher o.g… strange.
hmm
so 8 gallons to 6.75 is 10% and expected OG of 1.070 which is not out of line with your readings.
Ok… so I wasn’t that far off. It just seems most of my beers achieve relative higher OG’s than this one. Either way, it should drink just fine… just a lower ABV than I was expecting.
8 gallons boiling down to 6.75 is about 15%. Down to 6.25 would be over 20%.
When you say mash OG, I assume you mean in the kettle before boiling and after all sparging?
My guess is that there was some stratification somewhere and one of your measurements is wrong.

Hmmm . . . failure to adjust for temp? Weaker than expected boil? Shorter than expected boil due to daylight savings?
That happened to me. I was making a beer and started the boil at 1:59am and it one minute it was already 3:00am?!?! Threw me right off. 8)