So, I brewed a SNPA clone and overshot the OG by 8 points. I also ended up with about 1/3 of a gallon less than I was shooting for. Will I do anything detrimental by topping up with an extra 1/3 gallon?
1/3 gallon should lower your gravity by 4 points.
Sweet. That’ll make it only 4 points high and I’ll hit my volume.
If the beer is already fermenting or finished, I’d boil the water to drive off the air and cool quickly then add it so you minimize oxidation.
Coming in too high on your post boil gravity is a great problem to have. You can, as others have said, just add top off water and your numbers are fixed. Obviously, your question is how much water?
I love Brewzor, a free Android app, on my phone for this. It has a section for brewing calculators that I use constantly. One of them is a Gravity Correction calculator that will solve your problem for you. BTW, I have no commercial or financial interest in this program. I just think it is really helpful.
this has also happened to me.
I now take a pre-boil OG by removing the hydro sample after the sparge and at my virtual post boil volume) and before adding water (to make up my pre-boil volume). Stirring VERY well is crucial, If the gravity reading is over, I have time to adjust the hopping and volume, if under … same.