Author Topic: Hops IBU calculations  (Read 15766 times)

Offline GuitarLord5000

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Hops IBU calculations
« on: July 12, 2010, 12:25:19 PM »
Hello,

Some time ago, I created an Excel based brewing spreadsheet that has similar features to Beersmith.  I've always been happy with it's accuracy, as all of it's calculations are nearly identical in every respect to those from Beersmith.  Very recently, I've been discussing IBU calculations with the designer of an up-and-coming brewing software utility, and I'm beginning to wonder if there might be a minor error in Beersmith's (and my own) default Tinseth IBU calculations.
According to various online sources, the Tinseth formula is used to figure out IBU's based on whole hop cones in the boil.  Upward percentage adjustments can then be made to take into account the increase in IBU's from using Pellet or Plug hops.  For my spreadsheet (and Beersmith?), I assumed that the formula figures out IBU's based on Pellet hops, and so I make a downward percentage adjustment to get my whole leaf and Plug hop bitterness units.
By using pellet hops as the Beersmith default, are we in fact getting lower than actual IBU figures?  Or are the online sources wrong in that the Tinseth formula doesactually calculate for Pellet hop IBUs?

Sample Recipe:
Batch Size - 5.5 Gallons
Malt Bill - 5 lbs of 1.038 grain
Hop Bill - 1 ounce of 5.2 Alpha Acid hops - Boiled 60 minutes
OG Estimated at 75% efficiency - 1.026

IBUs = 20.7 (Pellet or Whole Hops?)

If Whole Hops is used as the default:
Whole = 20.7 IBUs
Pellet = 22.77 IBUs
Plug = 22.36 IBUs

If Pellet Hops is used as the default:
Whole = 18.6 IBUs
Pellet = 20.7 IBUs
Plug = 19.1 IBUs

Cheers,
Dave

Offline BeerSmith

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Re: Hops IBU calculations
« Reply #1 on: July 12, 2010, 05:33:26 PM »
Dave,
  Its been a few years since I went through these in detail.  I believe BeerSmith does use pellet as the default, but there are adjustments in the options dialog you can set for pellet and whole hops adjustments off the baseline.

Cheers,
Brad
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Offline GuitarLord5000

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Re: Hops IBU calculations
« Reply #2 on: July 13, 2010, 07:36:44 AM »
Dave,
......there are adjustments in the options dialog you can set for pellet and whole hops adjustments off the baseline.

Yes, I realize that you can make adjustments off the baseline IBUs.  What I'm saying is that I believe that the baseline for Beersmith's IBUs might be incorrect, or at least not as the creator of the formula intended.  The Tinseth formula (supposedly) gives you an IBU baseline for Whole Leaf Hops.  What I believe is that Beersmith takes that IBU number gained from the Tinseth formula, and applies it to Pellet hops, instead of Whole Leaf hops.  If that is the case, then you can make adjustments to Leaf Hops (+0%) and Plug Hops (+8%) to accurately reflect the Tinseth formula, but you cannot make an adjustment to Pellet hops (+10%) to correctly attain a Pellet hops IBU calculation.
If my theory is correct, and at this point I strongly believe that it is, an additional box would be needed in the 'Hop Type Utilization' area of the Bitterness options for Pellet Hops.  Or perhaps change the baseline IBUs from Pellets to Whole Leaf hops, and change the Leaf Hops Adjustment box to Pellet Hops Adjustment.
Anyway, I would love to hear your thoughts on this.

Kindest Regards,
Dave

Offline MaltLicker

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Re: Hops IBU calculations
« Reply #3 on: July 16, 2010, 09:02:33 PM »
Tinseth Method

"Glenn Tinseth's method doesn't involve as many factors, but is still a bit more complex than the original Rager method.Tinseth notes that his table is optimized for fresh whole cones loose in the boil, although easily adjustable for other forms of hops. He builds the gravity adjustment into the utilization tables and offers the following:"       http://www.realbeer.com/hops/FAQ.html

Brad - Tinseth's table is based on whole leaf, and the adjustment factors in BSmith are for whole leaf and plug.  On the face of it, that would mean you would have had to modify every single number in the table to make it "pellet default" so that a leaf hop (or plug) adjustment would be necessary.  

If the table used in BSmith is whole leaf default, then adjustment factors for pellet(+) and plug(?) would be expected.

Definitely worth a look under the hood.  
« Last Edit: July 18, 2010, 12:52:18 PM by MaltLicker »

Offline BeerSmith

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Re: Hops IBU calculations
« Reply #4 on: July 17, 2010, 10:57:12 PM »
Hi,
  Thanks - I will certainly take a look at this.  Unfortunately I'm on vacation at the moment and don't have access to my notes.  It is always possible I made a mistake here but it was quite a few years ago that I wrote the original code so I will need to take a close look at it first.

Brad
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Offline MaltLicker

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Re: Hops IBU calculations
« Reply #5 on: July 18, 2010, 10:40:26 AM »
The good news is that (if true) we're still just talking of limited effects on "theoretical" calculations.  

A 10% swing in a 50 IBU brew is 5 IBUs, which is less than the oft-quoted taste-able range of 10 IBUs.  
« Last Edit: August 07, 2010, 07:05:51 AM by MaltLicker »

Offline GuitarLord5000

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Re: Hops IBU calculations
« Reply #6 on: July 18, 2010, 11:25:48 AM »
Certainly, there is no formula that can boast accuracy.  The Beersmith program can, at best, ensure that the IBU formula is accurately represented.  And it's true that we're talking about a limited margin of error (about 15% at it's worst) on a formula that is already flawed.  Still, I think it's important to ensure that the program is calculating the formula correctly, if only to eliminate confusion with cross platform users and those of us that still calculate some things by hand.

If you take the statement that MaltLicker posted about the Tinseth formula being based on Whole Leaf Hops at it's face value, then I am just about positive that the Beersmith Tinseth calculation is flawed.  I base this statement on my own calculations, which are backed by Glenn Tinseth's Javascript calculator:
http://www.realbeer.com/hops/bcalc_js.html

Once you find some time to dig into this, I'd really like to know what your findings are.  This is the sort of discussion that the beer geek in me really enjoys!

Cheers,
Dave

Offline MaltLicker

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Re: Hops IBU calculations
« Reply #7 on: August 07, 2010, 07:06:25 AM »
Hey Brad

Any news on this question?  thanks.

Offline GuitarLord5000

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Re: Hops IBU calculations
« Reply #8 on: August 09, 2010, 04:48:13 PM »
Here's an email exchange I had with Glenn:

From me:
Hey Glenn,

A couple of us beer nerds have been having an ongoing discussion about your Bitterness formula.  You could really help us out if you could answer one question for us.  The Tinseth IBU Formula...does it calculate Whole Hops bitterness, or Pellet hops bitterness?  Which is it optimized for?  I see a few source online that claim it is for Whole Hops, but I figured an answer from the source would be best.

Thanks a ton!

Cheers,
Dave


And Glenn's reply:
All of my experiments were carried out using whole hops. I never used pellets at all.

Various folks have come up with estimates for the use of pellets with my formula, but they have no basis in experimental results.

Glenn

If you ever read this, thanks for the reply Glenn!  You're aces, mate!

So yes, the Tinseth formula is intended to calculate for Whole hops, not pellets.  Given that information, I'm quite sure that the Beersmith program is calculating Glenn's formula incorrectly.

Cheers,
Dave

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Re: Hops IBU calculations
« Reply #9 on: August 09, 2010, 08:12:01 PM »
Thanks Dave,
  If that is truly the case I will certainly look at modifying it on the next update.  I'm sorry for not getting to this sooner - I've been moving cross country, changing jobs and taking some vacation.  I'm planning to get back to BeerSmith and focus on the new version starting next week and the Tinseth calculations are at the top of my list to look at.

Brad
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Offline MaltLicker

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Re: Hops IBU calculations
« Reply #10 on: August 10, 2010, 06:35:41 PM »
Cool - make the best even better. 

To me, this helps make the case for somehow displaying the IBU model (Tinseth, Rager, etc.) and the personal settings in place, such as -10% for whole leaf, and ?? for first-wort hopping, in Recipe View. 

When I share a recipe, I could use Rager and a -10% for FWH, and others might be using Tinseth and +10% for FWH, and they'd have to know to dig down into the Options basement to determine my settings.  And if they change to their usual settings, it would throw off the numbers, including BU:GU. 

And it would be great to have $ codes for custom text reports.