[flbrewer]

I believe I read that IBU's can rise when you use more than x amount of water in an extract boil. How is this?

[dzlater]

The theory is that higher gravity wort will have a lower level of hop utilazation.
So the thinner the wort the more bitterness one would get from the same amount of hops.

[hubie]

John Palmer has a nice table (Table 7) that shows hop utilization percentage as a function of boil time and wort gravity:  http://www.howtobrew.com/section1/chapter5-5.html

Pick a boil time, say 60 minutes.  You get about 28% utilization from your hops if boiling in a 1.030 solution whereas you only get about 18% if you were boiling in a 1.080 solution.  This isn't all that big a deal for people who do full-boils, but if you're doing partial boils using extract, this could become an effect you'd want to compensate for (in this example, you'd want to increase your 60-minute hops by about 50%).

[a10t2]

The other thing to keep in mind is that the solubility limit for alpha acids is around 100 IBU. So if you're doing a 3 gal boil and diluting to 5.5 gal, for example, you can never exceed 100*3/5.5 = 55 IBU, give or take. If you've developed a recipe that takes advantage of that without realizing it, switching it to a less dilute concentrated boil could result in increased bitterness.

[morticaixavier]

The other thing to keep in mind is that the solubility limit for alpha acids is around 100 IBU. So if you're doing a 3 gal boil and diluting to 5.5 gal, for example, you can never exceed 100*3/5.5 = 55 IBU, give or take. If you've developed a recipe that takes advantage of that without realizing it, switching it to a lessmore-dilute boil could result in increased bitterness.

fixed that for you. but the concept is there. if you dilute less post boil you will get better hop utilization

[a10t2]

Yeah, that. I've had coffee now.

[saintpierre]

This is one of the reasons extract brewers tend to add a majority of the extract with 5 or so minutes left in the boil to get a better hop utilization.

[flbrewer]

This is one of the reasons extract brewers tend to add a majority of the extract with 5 or so minutes left in the boil to get a better hop utilization.

I've never done that, what am I missing?