IBU confusion

I've got a beer in the fermenter now that I calculated at ~37 IBUs using Palmer's nomographs in How To Brew. When I put it into BeerTools I was shocked to see 60 IBUS!

Why do I get wildly different IBU figures? Which one is correct?

my recipe:
3 gal boil
6 lbs. Briess Gold LME
.5 lbs. Victory
1 oz. Galena 13% for 60 minutes
2 oz. Cascade at knockout

At a guess, did you put the 3 gallons into BeerTools?

I'm guessing Palmer's 37 IBUs was for a five gallon batch. I'm guessing you boiled 3 gallons and added another 2 gallons at the end. If that's the case, once you were done boiling, that 3 gallons of wort was 60 IBUs, but after you added about 2 gallons of water it'd be down to about 40 IBUs, which you expected. Does that explain it?

According to Beersmith, the 60 IBU number is closer to accurate (for a 3 gallon batch). If you are topping up an extra 2 gallons... the number drops.

When did you add the malt extract? All of it at the beginning? with only an ounce of bittering hops, no way you got 60 IBUs! More like 34.

Is this a 5 gallon batch? I'm guessing you added water after the boil?

With a 5 gallon batch, I'm getting close to 60.

With a 3 gallon batch, I'm getting close to 100.

maffewl said:

According to Beersmith, the 60 IBU number is closer to accurate.

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Haha- we posted at the same time, but gave you exact opposite answers.

With one ounce of 13% AAU hops, I don't see how you could have possibly got 60 IBUs! Not in a 5 gallon batch. A partial boil may decrease hops utilization, but not all that much. I still stand by the 34-37 IBU estimate.

Adding an ounce is hops at 60 minutes is almost always going to add a high amount of IBU's because that is where all the bittering comes from. I'm not familiar with the How to Brew nomographs, but FWIW ProMash gave me the same reading that you got. I would say user calculation error, or just outdated information?

Yooper said:

Haha- we posted at the same time, but gave you exact opposite answers.

With one ounce of 13% AAU hops, I don't see how you could have possibly got 60 IBUs!

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Lol... I set it up for a 3 gallon batch... misread the OP saying boil.

maffewl said:

Lol... I set it up for a 3 gallon batch... misread the OP saying boil.

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Yeah, I saw this as a 5 gallon batch with a 3 gallon boil.

Yooper said:

With one ounce of 13% AAU hops, I don't see how you could have possibly got 60 IBUs! Not in a 5 gallon batch. A partial boil may decrease hops utilization, but not all that much. I still stand by the 34-37 IBU estimate.

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We're assuming hop pellets, correct?

http://www.rooftopbrew.net/ibu_calculator2.php

The responses in this thread are IBU confusion.

Here is what I put into Beer Smith

3 gallon boil
5 gallon batch
6lbs LME for 60 minute boil
.5 lbs victory
1 oz. Galena 13% for 60 minutes
2 oz. Cascade at knockout

I got 36.5 IBU.

If you did a 3 gallon batch with a 3.43 gallon boil you would get 66.1 IBU

h22lude said:

Here is what I put into Beer Smith

3 gallon boil
5 gallon batch
6lbs LME for 60 minute boil
.5 lbs victory
1 oz. Galena 13% for 60 minutes
2 oz. Cascade at knockout

I got 36.5 IBU.

How are you guys getting 60 and 100?

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Well, my quote of 100 was given with the possibility that you meant a 3 gallon batch. With a 5 gallon batch using Rooftop Brew's IBU Calculator, I got this:

http://www.rooftopbrew.net/ibu.php

Well, sometimes common sense is just as important as brewing software!

Think about it for a minute. There is a limit to the amount of IBUs that can be dissolved in any wort. That is 100 IBUs in theory. No WAY 13% AAU hops for an hour can come near that. No way.

Then, you add 2.5 gallons of water (IBUs of 0) to the wort. Even if the wort had 100 IBUs, which it certainly doesn't, adding 50% water would water it down to 50 IBUs.

I'm not saying I know everything- but in this case no way this beer has more than 50 IBUs. No way. 34-37 is a good guestimate.

It was a 5 gallon batch, with a 3 gallon boil. All malt extract was added and returned to a boil before adding hops and starting the timer. I used pellet hops.

Palmer's book says that the human palate can only discern increments of about 5 IBUs so any of the popular bitterness equations will be close enough. But there's a big difference between 34 and 60! And this is in a relatively light beer, too.

I have now taste tested the beer and can say that 60 IBUs is a massive overestimate. I'm still stumped as to the cause of the discrepancy. At this point, I wouldn't want to trust BeerTools for formulating a recipe. If I had used their figures I'd have a strange bitter-less beer on my hands.

TomOliver said:

Well, my quote of 100 was given with the possibility that you meant a 3 gallon batch. With a 5 gallon batch using Rooftop Brew's IBU Calculator, I got this:

http://www.rooftopbrew.net/ibu.php

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100 still wouldn't be right.

If the OP was doing a 3 gallon boil and then topping off to make it 3 gallons again, the IBU would be 61.

If he was doing a 3 gallon batch by boiling 3.43 gallons and not topping off, IBU would be 66.

If he did a 3 gallon boil and topped off to 5 gallons, IBU would be 36.5

If he did a 5 gallon batch with a 5.7 gallon boil, IBU would be 50.

Hop utilization would be different in all cases. The lower the amount of the boil, the more utilization you get. If you then top off, your IBU will go down from there.


It seems like he did a 3 gallon boil and topped off to 5 gallons. IBU of 36.5

Okay, well 90 is closer to the rooftop calc. Is the Rooftop Brew's Calculator incorrect?

TomOliver said:

Okay, well 90 is closer to the rooftop calc. Is the Rooftop Brew's Calculator incorrect?

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Again, I don't know that calculator. But if the max you can get into any wort is 100 IBUs, and you have a 3 gallon boil and add 2 gallons (but I assumed it'd be more like 2.5 and 2.5, since there is boil off) you'd have 50 IBUs or less automatically. But if 90 is the calculation, why not consider that adding 1/2 water would then "water down" the IBUs to 45 IBUs? That's sort of my guestimate anyway, but I'd be willing to bet it'd be more like 40 or less because 13% AAUs probably wouldn't give you 90 or 100 IBUs in a 3 gallon boil anyway.

Edit- well, do this! Change the OG of the boil, because with 6 pounds of extract the boil is more like 1.070+ OG. Then lets compare my thoughts against your software, keeping in mind that I did NO calculations, and trusted the OP's calculations and guessed the rest.

Yooper said:

Again, I don't know that calculator. But if the max you can get into any wort is 100 IBUs, and you have a 3 gallon boil and add 2 gallons (but I assumed it'd be more like 2.5 and 2.5, since there is boil off) you'd have 50 IBUs or less automatically. But if 90 is the calculation, why not consider that adding 1/2 water would then "water down" the IBUs to 45 IBUs? That's sort of my guestimate anyway, but I'd be willing to bet it'd be more like 40 or less because 13% AAUs probably wouldn't give you 90 or 100 IBUs in a 3 gallon boil anyway.

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I never said that a 5 gallon batch with 1 oz of 13% would be 90 IBU's. I was only trying to show where I pulled that number. I completely understand what you're saying about dilution.

It looks like Rooftop is incorrect.

Even with a 3 gallon boil using the OPs recipe, IBU should be just over 60.

Your input seems to be correct...except for the 50 minute boil which isn't a big deal. The OG is between 1.043 and 1.048 which is what you have. 1 oz of 13% hops for the full boil. Your batch size is 3 gallons using Rooftop but the IBUs with a 3 gallon full boil batch should be just over 60..not almost 90

h22lude said:

It looks like Rooftop is incorrect.

Even with a 3 gallon boil using the OPs recipe, IBU should be just over 60.

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I hate to pick this to death, but can you explain how? It just doesn't add up at all to me.

Well I think we are all on different levels here.

If we say he did a 3 gallon full boil for 60 minutes and did not top off so that would leave about 2.6 to 2.5 gallons of wort, IBU would be 70-71.

I was saying he did a 3 gallon boil and then topped back off to 3 gallons which would bring the IBU down to 61

If we took the 3 gallon full boil with no top off...

OG would be about 1.072 which would be a hop utilization of .2...real rough estimate
AAU of 13 (1oz * 13%)
IBU = 13 * .2 * (75/3) = 65...this calculation is always an estimate because hop utilization is not always exact.

h22lude said:

If we say he did a 3 gallon full boil for 60 minutes and did not top off so that would leave about 2.6 to 2.5 gallons of wort, IBU would be 70-71.

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Right. But with an IBU of 70-71 in the 3 gallon boil, topping off to 5 gallons (assuming a .5 gallon boil off) with 50% water would equal...........35 IBUs.

Yooper said:

Right. But with an IBU of 70-71 in the 3 gallon boil, topping off to 5 gallons (assuming a .5 gallon boil off) with 50% water would equal...........35 IBUs.

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Exactly. The calculation above was for a 3 gallon boil with no top off. I think we just started talking about differen batch and boil sizes.

A 3 gallon boil with a top off to make a 5 gallon batch would be ibu of 35 to 37, like you said

Still no clue why BeerTools quotes a much higher IBU. But, at least I know I didn't massacre my beer with IBUs.

Not to state the obvious, but did you change the % on the hops to match the % you mentioned (13%) or was it defaulted at a higher rate?

Also, would the % of Cascades be important to know even though it is at flameout? (sorry if I missed that one).

*wants to also be confused*

The only way that I can see that program spitting out 60 IBUs in the final volume is if it used *3* gallons in its correction factor (75/final volume) instead of the full *5*. Since IBUs are nothing but a measurement of the solution, that could throw it way off:

What could've happened:

98 IBUs = 13% * (75/3) * U% (~.3) --> when those ~98 IBUs @ 3 gallons is introduced to 2 more gallons (3/5 = .6) --> 98/.6 = ~60

But it should be closer to 35 IBUs...

Yambor44 said:

Not to state the obvious, but did you change the % on the hops to match the % you mentioned (13%) or was it defaulted at a higher rate?

Also, would the % of Cascades be important to know even though it is at flameout? (sorry if I missed that one).

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Flame out...no IBUs so % isn't a factor