Boil volume and IBUs

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binkman

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Hi all. I'm missing something.

So I brewed my first batch from a kit, and now I'm ready to dive in way over my head. And I have.

I'm brewing a batch without a kit, and I have piped all the information into some brewing software. I thought it was all fine, until I started tinkering with the boil volume. Now, everythings wonky.

Previously, I had an IBU value of around 22. The program was assuming that based on a 6.08 gallon boil, however. I have a 6-gallon brew pot and a 6.08 gallon boil seems more than a little impossible. The recipe I made from the kit called for a 2.5 gallon boil, then I added water.

Ok fine, so I have to increase the hop boil amount/time ratio to increase IBUs. I get that. But I feel like I'm missing something: I put in the kit's recipe and ingredients into my software and guess what? Everything was fine until I adjusted the boil to a 2.5 gallon boil like the instructions said. When I did that, the 10-13 IBUs they were saying I would end up with dropped to 6. Is the kit wrong? Is the program wrong? Or am I failing to take something into consideration? I don't want to brew a 5-gallon batch of underhopped beer, if another coupe ounces can make all the difference. At the same time, I don't want to overhop it. I'm shooting for a style calling for 20-28 IBUs.

Any help would be appreciated, thanks!
 
Try putting the info into some online free calculators.

I like:

http://www.fattymattybrewing.com/ho...hp?page=tools&section=bitterness&action=entry

because it uses 3 separate ways of calculating IBUs.

I use my own spreadsheet now which also calculates IBUs several ways but I've found Tinseth's calculations to gel best with my tastes.

Not sure why the numbers are different from those in the kit. Do you have the AA% correct? Did you enter the boil times exactly as written? Did you adjust for volumes at the start of the boil and for the final volume after topping off?
 
Not sure why the numbers are different from those in the kit. Do you have the AA% correct? Did you enter the boil times exactly as written? Did you adjust for volumes at the start of the boil and for the final volume after topping off?

The AA is correct. Even messing with it, though, it'd have to be way off to make up for the difference.

Boil times exactamundo.

Adjusting volumes check. Actually, I didn't add the volume of the liquid extract to the 2.5 gallons of water the kit recipe called for. Could this be the problem?
 
In fact, adding the LME volume, which i assume to be about 10 fl oz. to the lb., brings it back almost within the correct range. Kit would yield 9.3 IBU, kit recipe calls for final IBU of 10-13.
 
There can be pretty big variation in the 3 dominate ways of calculating IBUs. The kit may use a different one and that could certainly correct the little bit of difference you have left after the LME.
 
The AA is correct. Even messing with it, though, it'd have to be way off to make up for the difference.

Boil times exactamundo.

Adjusting volumes check. Actually, I didn't add the volume of the liquid extract to the 2.5 gallons of water the kit recipe called for. Could this be the problem?

No. It is 80% solids so the water volume isn't going to be significant. Why don't you list your planned hop schedule?
 
Okay, so the kit broke down like this:

Steep 1 lb specialty grains in 2.5 gallons of water for 20 minutes, then add 6.6 lbs of extract and begin boil.

Boil schedule: Add bittering hops (.5 oz at AA 4.5). After 40 minutes add flavoring hops (.25 oz at AA 4.2). After 20 minutes terminate boil. Cool wart, add enough water to make 5 gallons.

Program claims there will be 6 IBUs.

IBUs: 10-13, OG: 1049-1053, FG: 1012-1015, ABV: 4.75-5.25.

My recipe:

Steep 1.75 lbs specialty grain in 2.5 gallons of water for 20 minutes. Then add extract start boil.

Boil schedule: Bittering hops (1oz at 4.3 AA) 60 min from end, then flavoring hops (.5 oz at 3.3 AA) 30 min from end, then aroma (.25 oz 3.5 AA) 10 min from end. This leaves me with 11.5 IBUs.

If I increase the boil volume to 6 gallons, assuming I lose 1 gallon and don't have to add anything to my boil afterward, I get 20.8 IBUs.

PS, I'm running a mac and using BeerAlchemy.
 
I want to make sure I am understanding your issue.

You get 20.8 IBU for a full boil with your calculator.
You get 11.5 IBU for a partial boil with your calculator.
You get 44.9 IBU for a partial boil (before topping off) with the online calculator which then corrects to 18.7 adjusting for volume.

Is this correct?

If so, the online and full boil BeerAlchemy calculations agree but the BeerAlchemy partial boil does not? Is this correct?
 
My average IBU strength for my boiling schedule and 2.5 gallon start volume comes out to 44.9, (43.1 tinseth). This is of course the pre-diluted IBU. But why is my program so wrong? I've triple checked everything else.

So am I right to assume that if I add 3 gallons to what I assume will be 2 gallons of 44.9 IBU after the boil, that I need to calculate IBU as being now 40% of what it was undiluted? Leaving me with about 18 IBUs?
 
You get 20.8 IBU for a full boil with your calculator.
You get 11.5 IBU for a partial boil with your calculator.
You get 44.9 IBU for a partial boil (before topping off) with the online calculator which then corrects to 18.7 adjusting for volume.

Is this correct?

If so, the online and full boil BeerAlchemy calculations agree but the BeerAlchemy partial boil does not? Is this correct?

Yes, yes, yes. Yes. The BeerAlchemy partial boil does not agree with the online calculator partial boil (which is adjusted to 18.7). They only agree for the full boil volume. I guess my question is why is there such a disparity and which calculator is correct?
 
If you look around there are some threads here about utilization and wort concentration. The concentration of the wort is the only other thing I can think of that could be playing a role here if the last point did not answer your question.
 
The program may be set to severely adjust for wort concentration?

You end your boil with 1.100 wort if you end with a final OG of 1.050. Are you sure that the original recipe tells you to put all the extract in at the start of the boil?

Most extract recipes call for early and late additions. This would affect the wort concentration and would absolutely affect hop utilization and therefore IBUs. (Early additions also result in darker color)
 
The program may be set to severely adjust for wort concentration?

You end your boil with 1.100 wort if you end with a final OG of 1.050. Are you sure that the original recipe tells you to put all the extract in at the start of the boil?

Most extract recipes call for early and late additions. This would affect the wort concentration and would absolutely affect hop utilization and therefore IBUs. (Early additions also result in darker color)

I don't have an original recipe. I'm just improvising. The kit had me throw everything in at the beginning of the boil, so I was just going to emulate that. Even if that has an effect, I'm surprised the kit manufacturers would have failed to take it into account.
 
So I found this thread:

https://www.homebrewtalk.com/f39/question-hop-utilization-ibus-6001/

And according to el pistolero,
Turns out this is as big a controversy as glass vs plastic, but only among the truly geeky. The consensus seems to be that for partial boils, the Rager method is more accurate, while for full boils the Tinseth method is closer. Here's some light bathroom reading that goes into all of the whats and wherefores.

He lists a few different articles, one link is dead, but one especially helpful link is the following article.

The disparity between the online calculator and my program happened to be that the program was set to use only Tinseth. If I instead calculate Rager for my 2.5 gallon boil, and the kit's 2.5 gallon boil, I get values that make a lot more sense (at least in the kit's universe). The kit gets 12.2 IBU of an estimated 10-13 now, and my own recipe gets 19.8 IBU, whereas the original Tinseth full boil value, which I used to design the recipe, would have been 21.1. The author of the above linked article says he favors Rager in small boils, and it looks like the manufacturers of my kit must do the same, so I will follow suit.

In the end of course, I just need to brew this batch, keep a record of the recipe and procedure, and adjust accordingly next time. Unfortunately, it's a lager and it will be a while before the jury is back on this one.
 
Yeah. So it definitely sounds like others have determined its a difference in the method of calculation/theory.

My advice is go with full boils as soon as you can - even if you make four gallon batches instead of five. You will not be dissapointed with your results if you do this.
 
One other thing to keep in mind is not to get too wrapped up in the exact numbers. The taste threshold for most people is about 5 IBU so in theory there is no taste difference between 10 and 12 IBU. Now that you have your software issues figured out you should be good to go.

:mug:
 

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