I am doing a full volume boil using a partial boil recipe kit…is there a thumb rule for adjusting the bittering hop addition or should I just throw all of the hops in? Thanks!
You will get much more extraction thus higher IBUs for a full boil when compared to a partial boil. I would use less but its hard to say how much.
Have you tried to run the recipe through a calculator using both different volume levels to see what the corresponding IBUs would be?
If you want the nitty-gritty, you can read Palmer’s section on it here: http://www.howtobrew.com/section1/chapter5-5.html
It includes a handy nomograph to use for calculations.
The hop utilization numbers Palmer got from data taken by Tinseth. If it were me, unless I was going for something very specific in terms of bitterness, I would just toss the hops in and go with the higher IBUs. If I really wanted to try to correct for it, I would take a rough stab at it by looking up the utilization for the recipe pre-boil gravity and ratio that with the utilization for a full boil gravity. For instance, say your recipe has you boiling 3 gallons of 1.080 wort for 60 minutes. From the table that would be a utilization of 0.176. Now you want to boil 5 gallons for 60 minutes, so your pre-boil gravity is 3/5th 1.080 or 1.048, and your new utilization is about 0.230 or so, so you could cut your hops back to about 0.176/0.230 = 76 percent.
Edit: I used “efficiency” when I should have used “utilization” to keep the terminology consistent regarding hop usage
Thanks for the ideas…I am brewing this weekend and I think I will try both just throwing them all in and correcting for the full volume…in the end I am sure I will have great brew either way!