The Old Bitterness Calculation Problem

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PistolPatch

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I thought the following posted by the other 'Pat' on BIABrewer.info might interest a few of you. It's a brewing area that I have found the lack of logic and definition totally bewildering. If it weren't for guys like MHB and Gryphon, I'd still be thinking that there is something that I, personally, am not seeing in bitterness formulas let alone many other poorly defined figures.

When someone says, my beer has an IBU of x, even if you knew they meant Tinseth rather than Garetz or Rager you'd still have no way of knowing what they mean unless they used the same software and identical equipment. The same, of course, goes for the term, 'efficiency'.

It's a real shame that so many brewers never question their software let alone push to get the formulas made transparent.

The following is a copy of this post...

The Tinseth Bitterness Problem

A study of stux's thread here will soon show the reader how poorly defined the Tinseth hop formula is. Stux, ianh and myself have grappled with this problem many times expecting that, out there somewhere, there must be a Tinseth formula that has no obvious flaws. There isn't.

Over the last few days I have explored this area yet again, looking at four screens, five programs and many websites.

The problem with the Tinseth formula is that it refers to, "Gravity of the boil' and 'Volume of finished beer.' Depending on how you define these two things, you will end up with widely varying figures. None of us here have been able to determine what Glen Tinseth means by these terms. All of stux's and my interpretations come out lower than the mainstream programs but match more closely the online Tinseth original calculator.

Mainstream programs are not transparent so we don't know how they have interpreted the formula. We really don't know whether they are treating gravity as original gravity, average gravity during the boil or average gravity during the time of the hop addition. As for finished beer volume, we don't know whether they are using the end of boil volume, the end of boil volume once chilled, volume into fermenter or volume into packaging. We also don't know the history - did one program start with an interpretation and did others then apply a 'fudge' factor to replicate that interpretation?

So, what are we going to do?

The Utilisaton Curve

There is a great logic to Tinseth as can be seen from the graph shown here. This curve gives us something to work from and so we are definitely going to use the essence of the Tinseth formula.

The Gravity

We believe the most logical interpretation of 'gravity of the boil' for hop utilisation is the average gravity of the boil during the time of each individual hop addition. So we will use this in our formulas.

Volume of the Finished Beer

We also believe the most logical volume to use is the end of boil volume at ambient temperature (20 C). We are certainly not going to be arrogant enough to attempt adding in a delayed chill factor to allow for hot whirl-pooling or no-chilling.

An Adjustment Factor

ProMash has something they call a 'Concentration Factor' which has a default of 1.3 and aims to determine your average gravity during the boil. This indicates it treats every addition as having the same average gravity. BeerSmith2's hop tool requires the user to input batch size (this means volume into fermenter for this program) and pre-boil volume so this is another interpretation. BeerAlchemy comes up with totally different figures again. Other programs may have copied any of the above as best as they can assuming it is a correct interpretation.

The mainstream programs set perceptions so rather than having BIABrewer.info's Tinseth interpretation being always lower than the mainstream programs, we will add in an adjustment factor. To do this will require entering many varying recipes into many different programs and looking for the 'best fit'. At present, it looks like an adjustment factor of around 1.2 will work very well.

Summary

As Glen Tinseth will tell you himself, bitterness formulas are very primitive and, in real life, often worthless. For example, the AA% marked (if marked) on the hops you buy are a guess. They are taken from a small sample of a 200 lb (91 kg) bale and after this they are stored by a wholesaler, then shipped to retailers who may or may not refrigerate, let alone freeze them until you buy them.

So, before we even get to the mathematics of bitterness, we are really in very unreliable territory. We hope the above plan will bring at least some logic into this very messy area.

We have supplied other programs (such as BeerSmith2) with our latest BIAB figures. Other programs have simply pinched them from us with no acknowledgement :lol:. We'll continue to remain transparent though in our figures in the hope that, one day, all software will match. We certainly can't see any reason why they shouldn't match. At the moment though, with brewing software, one will say 2 + 2 = 3.5 and another will say 4.7 while we are all sitting around scratching ourselves saying, "Why don't they all equal 4?"

I hope accounting software isn't the same!

Cheers,
Pat
 

mje1980

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One of the things i like about beertools is you can use 4 or 5 different hop calcs, and get an average. Seems to work.
 

Nick JD

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Once you've got to know your set up it's pretty easy to adjust your hop bill to get the bitterness your tongue requires, not the software.

Known commercial examples are a good way of "zeroing" your IBU. I use the formulas as a rough guide.

Wouldn't there be bigger variables in the utilisation than volumes and SGs? How many people correct their IBUs for their hop's age? What's the deviation of the batch of that variety?

And what about "apparent bitterness" - how does the software calculate this? What about the fact that using the Alpha Acid percentage of a hop isn't a concrete figure for its bitterness, as there are other bittering compounds in the hop, and these ratios vary depending on variety?

Is this just like picking a bunch of hairs and deciding to only split one?
 

Lord Raja Goomba I

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Once you've got to know your set up it's pretty easy to adjust your hop bill to get the bitterness your tongue requires, not the software.

Known commercial examples are a good way of "zeroing" your IBU. I use the formulas as a rough guide.

Wouldn't there be bigger variables in the utilisation than volumes and SGs? How many people correct their IBUs for their hop's age? What's the deviation of the batch of that variety?

And what about "apparent bitterness" - how does the software calculate this?

Is this just like picking a bunch of hairs and deciding to only split one?
Probably, but I get the point.

I know with a certain grain bill for APA/AAA, I'll aim the software for a number, and it has to be broken down into how it gets accumulated (x IBU from 30 m, x from 15 and so on) - to hit the perceived bitterness I prefer with that grain bill.

New grain bill, it's a guesstimate using the software and then trial and error from there.

Goomba
 

felten

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Its hardly even worth fretting about. The formulas in the software are the best ones available, but they're still just models of something that is next to impossible to model.

As always, take your own IBU calcs with a pinch of salt and adjust to your own taste.
 

cdbrown

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How many people correct their IBUs for their hop's age? What's the deviation of the batch of that variety?
How would I do this? Cascade 09 hops 5%AA. What would the AA roughly be assuming it's been sealed and refrigerated?
 

Nick JD

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This is from Beersmith (copied it form another forum). Quite possibly, brewing software's factoring in the vintage (bintage?) of your hops is one of its best features.

Vacuum packed 0
0 months 6.9%
12 months 6.11%
24 months 5.42%
36 months 4.8%
48 months 4.25%
60 months 3.77%

Poly Bag 0
0 months 6.9%
12 months 5.42%
24 months 4.25%
36 months 3.34%
48 months 2.62%
60 months 2.06%


But has Beersmith got this wrong too? Pat might know.

This probably doesn't count the 12 hours your pierced vac-bag sat in a warehouse in Arkansas at 42C. Basically, it's a craps shoot. Use your tongue; get to know your ingredients with trial batches. Adjust where necessary.

I'd guess this why commercials test and "correct" with extracts (or just use them wholesale). And the next question is how does the degradation of bittering compounds compare to that of flavouring/aroma compounds?
 
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