IBUs bothering me...

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IBUs bothering me...

Postby bzwrxbz » Thu Mar 29, 2007 7:29 am

This was brought up in the past, and something related to it in the "Mash Tun Heat Capacity Confusion" thread.

When I have a finished recipe... I can go and lock the "Final Volume", and then drop the "Kettle Volume" very low, and in the meantime, the calculated IBU levels given in the Style/Bitterness tab do not drop.

I would expect that as my Pre-boil OG gets higher, my IBU values would drop, given that my hop schedule remains a constant, and my "Final Volume" remains contant/locked.

Why do the IBU levels not drop? Do I misunderstand something? Or, is this feature/correction not implemented in BTP yet?

thx. cheers!
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Algorithm

Postby jeff » Thu Mar 29, 2007 7:41 am

Which %U algorithm are you using?
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Re: Algorithm

Postby bzwrxbz » Thu Mar 29, 2007 7:50 am

jeff wrote:Which %U algorithm are you using?


Yes, I am an idiot... the "boil time" correction one was filled, but not the gravity correction dropdown.

It looks like there is HUGE deviation between the different types of gravity correction factors. I have a feeling they can not all be correct. :) Brewing is such a mystical/magical/black art sometimes.

Even one of them has the values going way above one for lower gravities. This makes me rethink how bitterness utilization works.

thx for the help, there is so much functionality, I can get lost sometimes LOL

cheers!
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Re: Algorithm

Postby jeff » Thu Mar 29, 2007 9:31 am

Come on, you're not an idiot. I just asked the question because it's the first thing I need to know to offer a solution. In this case, the solution happened to be an easy one.

bzwrxbz wrote:It looks like there is HUGE deviation between the different types of gravity correction factors. I have a feeling they can not all be correct. :) Brewing is such a mystical/magical/black art sometimes.


That's why I put all of them in there; I don't know which one is the most correct either :?
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Re: Algorithm

Postby ColoradoBrewer » Thu Mar 29, 2007 9:59 am

jeff wrote:...I don't know which one is the most correct either :?
I don't think there is a "correct" one. There are too many variables in the systems and methods used by homebrewers. I also think that because of these variables the IBU's calculated by the software are most likely not correct either. The only way to know the IBU's to an absolute certainty is by lab analysis. About all we as homebrewers can do is pick a utilization formula that seems reasonable, stick with it, and develop a perception for the IBU's it calculates.
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Postby slothrob » Thu Mar 29, 2007 10:32 am

The rule of thumb I've seen posted before is that the Tinseth formula gives a reasonably accurate prediction for a full volume boil with no top-up water nor late extract additions.
Rager's formula is supposed to more accurate for partial volume boils.
I know nothing about the other formulas.
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Postby ColoradoBrewer » Thu Mar 29, 2007 11:01 am

I've read that too. I've been using Tinseth since I do full volumes boils, but lately have begun to question if it's right for my system. My brews just don't seem to have the bitterness I'd expect from the numbers calculated. An I idea I have is to buy a commercial beer of known bitterness, brew a clone of the same beer and compare the two.
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Postby rrosa » Tue Apr 03, 2007 11:10 pm

I use Tinseth's as well since I also read it is the most accurate (didn't know that it was supposed to be the most accurate only for full volume boil, but that is what I do anyway). One doubt that I have is that I seem to recall reading that Tinseth's formula is for leaf type hops, not pellet, and the Pellet Type Hops correction is empty in Tinseth's algorithm implemented in BeerTools Pro. My other concern which applies to all algorithms is that I also seem to recall that the utilization reduces by a factor of about 15% when using hop bags, which I also use, and I don't see this factor in BeerTools. I hope this gets implemented in future releases. Assuming these two things are correct, their absence in the algorithm basically cancel out and I get a reasonably good approximation to OG. Finally, I have also read that it is hard to detect a difference of 5 IBUs when tasting the beer, so this approximation should be good enough indeed. But of course my assumptions could be wrong...
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Postby slothrob » Wed Apr 04, 2007 9:17 am

I think this is all correct, to my understanding.
However, if you select Tinseth, you have the option to enter a Pellet Hop Correction of your choosing. This can even be customized to correct for a hop bag, if you want. I often use whole leaf hops and a hop bag, so I use a customized -10% correction on those occasions.

I've also played with the curves so that I can enter FWH hops as 120' and get an equivalent of 20' utilization. :shock:
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Postby TCBrewguy » Wed Apr 04, 2007 9:54 am

I use the Tinseth algorithm for boil time and gravity also. Because I use a hop bag w/pellets, I use Jeff's pellet correction because it calculates a slightly lower utilization than some of the other correction algorithms.

BTW, since we're on the subject, I was wondering how you came up with your algorithm, Jeff. Is there a specific procedure it is designed for (i.e., loose hope pellets vs. hop bag)? Any chance you could shed some light? :)
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Postby rrosa » Wed Apr 04, 2007 9:58 am

Yeah, I thought about customizing the utilization. I sometimes use Hop Pellets Correction from other algorithm but I was too lazy to edit my own curve.

And in principle we could use hop bags for just some of the hop additions, and that is why I mentioned there should be a separate Hop Bag Correction factor, but I am not sure it is worth the trouble. Usually I guess we either use hop bags in all of the additions or none.
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%U Plans

Postby jeff » Wed Apr 04, 2007 10:38 am

There are plans to expand the %U algorithm to address some of its current limitations, including hop bags and FWH.

The current utilization algorithm is configured to receive input from the amount of time a hop addition is boiled. This is the primary means for extracting bitterness from hops. The boil time %U value is then multiplied by two correction values if they exist; gravity and pellet form hops. These receive input from the gravity of the boil and the "Form" setting from the individual hops.

The plan is to allow the algorithm to accept an unlimited number of correction/adjustment formulas which can be completely configured. Each formula will be based on a graph over time or gravity. The input value will be selected from none, hop form, hop bag, FWH, etc. If any of these evaluate to "true" then the correction will be applied to the %U value.

Obviously, it will be necessary to provide some presets; but the configurability of the system will accommodate any type of brewing. Of course it will be up to each brewer to decide which algorithm works best for his/her methods.
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