Originally Posted by missing link
My goal is to get the right volume pre-boil at the right gravity, boil off the right amount and get the correct post gravity at the correct volume.
So if I need 7.5 gallons at 1.042 pre-boil and I boil for an hour, I want to breally close to 6 gallons at 1.052.
A few of my past brews, I have hit my pre-boil gravity and volume, but totally missed my post boil gravity by as much as 10 points and I had more wort than I could fit in the bucket I just don't know how much more.
I'm going to try adding my spritzed with star san IC after the boil is done and measured.
Here is another question. What is more improtant then - is it boiling for exactly 60 minutes and getting the proper hop utilization or is hitting your OG more important?
Since you are hitting your target pre-boil volume and gravity, all that's left is to figure out your evaporation rate. Once you nail down your evaporation rate you'll be able to hit your target post-boil volume and gravity.
Fill up your kettle with 7 gallons of water and boil it for 60 minutes, just as you would if you were making beer. At the end of the hour measure how much water you have left. Your (hourly) evaporation rate is equal to
[ (pre-boil volume - post-boil volume)/(pre-boil volume) ] X 100
Enter that into BeerSmith, or whatever program you use to help you make recipes. This should be a good approximation to how much you boil off in an hour. Use this figure on your next brew day and if you hit your pre-boil gravity and volume, I bet you will be very close to your post-boil targets too.
Because I know the boil-off rate of my kettle, if I hit my pre-boil volume and gravity I know
that I'll hit my target post-boil vol and grav before I even begin the boil.