Two Questions - IBU & Half-Boil

So in using a new Beer program on the iPad I came across two questions that I would like to know.

1) I am going to be making an extract brew from Northern Brewer. It is an Imperial Stout (7.99%). It uses Summit Hops for the full 60 minute boil and gets an estimated IBU of 81.93. Is that high for a stout? I always was under the assumption that ~50 is the upper end for a stout. But does the fact that its imperial make having an 80+IBU ok?

2) In playing with some numbers in the beer program I saw that when I did a 5 gal full boil (accounting for boil off), that I got an IBU of 81.93. But when I adjusted the boil to 3 Gal (assuming that I will top of 2 gal at the end to make it 5gal total), I get an IBU of around 43. Why the large difference? Is this accurate? or is this just confusion on the brew software? I only have the ability to do partial boils with my 5gal stock pot right now, so I'm wondering why the numbers are showing the way they are right now.

Thanks guys and gals! :rockin:

1) Imperial stout should be 50-90+ IBU per style guidelines
2) the software is correct, partial boils mean higher gravity wort which will greatly affect hop utilization

cheers!

one other thing, if the software allows play around with adding a portion of the extract late like 15 min to go. Among other reasons to do this (search) it will increase your hop utilization.

chickypad said:

one other thing, if the software allows play around with adding a portion of the extract late like 15 min to go. Among other reasons to do this (search) it will increase your hop utilization.

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Current it 6 LBS of Dark Malt Syrup for 60 minutes and 6 LBS of Dark Malt Syrup for the last 15 minutes. However, when I played around with it (such as adding 1 Lb for the first 60 and the rest at the end) I'm still getting the same hop utilization. Ill do some searching though, because I've heard late extract helps.

^^^^ ehhhh... Some of that stuff about high gravity wort causing less utilization is beginning to get debunked by even a few of those who at once might have touted it.... The reason partial boils provide less ibus is due to the dilution of the wort when topping up. If in theory as a homebrewer, you could get 100 ibus into a 2.5 gallon batch of wort, and then diluted to 5 gallons, it would stand to reason that the finished beer could only be 50 ibus.... Ibus on the homebrew level ain't perfect, but NB has it right with trying to get 50 ibu or so In that beer by dilution. Also, I'm not in the camp that late extract additions do much of anything for utilization.. It may be a percieved difference..They do however offer less carmelization and a truer color of the finished beer.

hmm, maybe it's not as much of an effect with all extract. when I plug my partial mash batches into Beersmith and add all the extract at flameout vs 60 min it seems to calculate about 15-18% higher IBU.
I would check out the arguments for late extract though, I do think it helped my lighter beers.

duckmanco said:

^^^^ ehhhh... Some of that stuff about high gravity wort causing less utilization is beginning to get debunked by even a few of those who at once might have touted it.... .

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well there you go. didn't know it was one of the myths!

^^^ I'm not saying its a myth just yet, it's that lately, guys like Palmer have been saying that more and more lately wort gravity appears to be unrelated to AA utilization. I agree with it because I can't taste a difference. Where I taste a difference is when doing a late extract addition and the wort doesn't suffer from carmelization.

What program is it?

Oddball said:

What program is it?

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iBrewMaster on iPad.

One of the issues with a partial boil and IBUs isn't really related at all to the gravity of the wort and utilization.

BUT, remember that there is a maximum that isomerization can reach (only so much oil can isomerize). The thinking on this is that it's about 100 IBUs, more or less. That of course isn't an issue, as that's about the threshold for the human tongue anyway.

However, when you're doing a partial boil, that means the max IBUs you can get into any beer is limited by the amount of water you add. What I mean is this- say you've got a ton of bittering hops in a 2.5 gallon boil, for 100ish IBUs. When you add 2.5 gallons of water (0 IBUs), that means that your IBUs will be cut in half.

The "cure" to that is to boil as much volume as you can, and lower the amount you top off with.

This isn't usually an issue for most beers, but if you're only boiling 2.5 gallons you'll pretty much be limited to 50 IBUs or so just from dilution.

Brak23 said:

iBrewMaster on iPad.

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Thanks...

Yooper said:

One of the issues with a partial boil and IBUs isn't really related at all to the gravity of the wort and utilization.

BUT, remember that there is a maximum that isomerization can reach (only so much oil can isomerize). The thinking on this is that it's about 100 IBUs, more or less. That of course isn't an issue, as that's about the threshold for the human tongue anyway.

However, when you're doing a partial boil, that means the max IBUs you can get into any beer is limited by the amount of water you add. What I mean is this- say you've got a ton of bittering hops in a 2.5 gallon boil, for 100ish IBUs. When you add 2.5 gallons of water (0 IBUs), that means that your IBUs will be cut in half.

The "cure" to that is to boil as much volume as you can, and lower the amount you top off with.

This isn't usually an issue for most beers, but if you're only boiling 2.5 gallons you'll pretty much be limited to 50 IBUs or so just from dilution.

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So if I have an electric stove and a 20qt (5 gal) stockpot. What is the max boil I should go for? One beer I had it pretty full (let's say 5 gal). But it never truly boiled. Obviously my next step is to invest in some sort of propane burner. But for now... 3 gal maybe?

Brak23 said:

So if I have an electric stove and a 20qt (5 gal) stockpot. What is the max boil I should go for? One beer I had it pretty full (let's say 5 gal). But it never truly boiled. Obviously my next step is to invest in some sort of propane burner. But for now... 3 gal maybe?

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Well, I'd say boil as much as you can. It needs to boil, in a rolling boil, for the 60 minutes. You could add the bulk of the extract late so that you can boil more liquid volume. I'd try the stove with water and see. Start with 2.5 gallons, and bring it to a boil. Add .5 gallon and see if you can still maintain a boil. If you can, add a little more. Then you'll know the max your stove can boil.

Yooper said:

Well, I'd say boil as much as you can. It needs to boil, in a rolling boil, for the 60 minutes. You could add the bulk of the extract late so that you can boil more liquid volume. I'd try the stove with water and see. Start with 2.5 gallons, and bring it to a boil. Add .5 gallon and see if you can still maintain a boil. If you can, add a little more. Then you'll know the max your stove can boil.

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Thank you! You have been super helpful! I'll give it a shot.

The idea that utilization is reduced in a higher gravity boil is based on the fact that soluble compounds will be less so in water that is already partly saturated. In general, this is unassailable and stone cold fact - there is a limit, for a given pressure/temperature state, to the quantity of solubles water can hold. When every polar water molecule is matched up to an oppositely polarized solute (sugar or hop compound) the water is saturated and, with all due respect to John Palmer, won't dissolve anything else. The questions are, how saturated is high gravity wort, and how does solubility drop with gravity? Clearly, given that there are barleywines with OG higher than 1.1, ordinary worts aren't fully saturated, but they will be partially saturated, and without a doubt there will be reduced solubility of hop compounds - the question is, will it be significant and how much added hops will compensate? I've been under the impression that utilization corrections, like the one in Beersmith for example, were based on scholarly research, but I confess I've never dug into the literature. I'd be willing to bet that it's out there.
You should keep in mind that IBUs ARE NOT a measure of perceived bitterness and ONLY take the solution chemistry into account (that's why a heavy, malty, sweet Imperial needs more IBUs to achieve the same perceived bitterness) - your taste buds are the ultimate judge.