• Welcome to the new forum! We upgraded our forum software with a host of new boards, capabilities and features. It is also more secure.
    Jump in and join the conversation! You can learn more about the upgrade and new features here.

tinseth bitterness calculation does not use average wort gravity?

alanmcl

Apprentice
Joined
Aug 27, 2020
Messages
7
Reaction score
0
Playing with BeerSmith's Hop Bitterness calculator I note that it's plugging the starting wort gravity instead of the average wort gravity into Tinseth's formula.

I found an old thread about this here: http://www.beersmith.com/forum/index.php?topic=13057.0
But the resolution is unclear and the link to a "more approriate thread" 404's for me now (http://www.beersmith.com/forum/index.php/topic,13062.0.html)

Tinseth's article pretty clearly says "average wort gravity" (https://www.realbeer.com/hops/research.html)
What's the reasoning behind BeerSmith's difference here?
 
I don't know Brad's original thinking behind using the pre-boil gravity instead of the average boil gravity.  I also have not bothered to go back through the calculations to check to see if he has changed it in the most recent versions. 

Honestly, to me it really does not matter.  Calculated IBU is only a rough correlation with the perception of bitterness given the current methods of hop addition and the differences in processes between what I do and what Glenn did to validate the utilization curve.  I use it as a benchmark and from comparison of my beers versus commercial beers with reliable IBU values (Sierra Nevada and Sam Adams are probably the best to benchmark against) I know how where to target the calculated IBU to get the bitterness impression which I am targeting.  I also adjust the whirlpool/steep temperatures in the program (actual values differ from the values used to regulate the calculated response) to give me the perceived bitterness which matches the IBU target the program spits out.  This I have worked out through a series of brews with whirlpool hops only and comparing to beers with a range of bitterness.



 
Thanks for the reply @Oginme

I'm also not especially worried by the IBU accuracy; I'm just busy working things through from first principles for my own understanding.

Let me expand a bit though.
The only way I can match the result from the Hop Bitterness tool to my own Tinseth calculations are to use the pre-boil gravity.
That result also sometimes matches the result in the recipe "Design" tab, but also sometimes not.

Here are the field mappings I'm using

tool "Batch Volume" = recipe "Batch Size" on the Design tab
tool "Boil Volume" = recipe "Est Pre Boil Vol" on the Session tab (editing this field doesn't seem to impact the tool output though)
tool "Boil Gravity" = recipe "Est Pre Boil Gravity" on the Session tab
tool hop addition = same as the recipe including AA, boil time, hop form, everything

For example: I set up a new recipe using the pre packaged 'All Grain - Standard 5 Gal/19l Batch - Cooler' equipment.
That sets the batch size to 17.2L, pre-boil vol to 22.92L
- add 5kg of "Pilsner (Weyerman)". This sets the pre-boil gravity to 1.048.
- add 100g of Tettnanger (4.5% AA, pellets) at 60min. The Design view lists the IBU contribution here as 57.6 IBU.

Plugging those same values into the Hop Bitterness tool I get 67.3 IBU.

What am I missing that explains this difference?

I've attached this bare-bones recipe as a bsmx file.
 

Attachments

  • test_ibu.bsmx
    14.5 KB · Views: 1
Just at a quick glance, I would think that the difference comes in with the trub loss after boil.  The stand alone bitterness calculator does not know that your difference in volume from the pre-boil to the fermenter volume is not all boil off, so it concentrates the estimated IBU more in the calculator.  The recipe design has the figures calculated for end of boil which sets the concentration of bittering components and then removes the trub loss which results in a lower value.
 
I think you are right. Setting the equipment trub+chiller loss to 0 brings the two results to within a rounding error (57.7 vs 57.6).
Updating the field mapping in the tool as follows brings the same result:
tool "Batch Volume" = recipe "Est Pre Boil Volume" on the Design tab MINUS equipment "Trub & Chiller Loss".

The rounding might be off because of me using metric units in the UI and the calculations being in USian units under the hood.

It's a bit odd because Tinseth's equation uses "volume of finished beer" which would imply BeerSmith's "Batch Size", where in fact BeerSmith is excluding any boil & cooling evapouration losses.

Still as you say IBU accuracy to this level isn't worth stressing over. I'm satisfied that I've tracked down how the numbers are worked out.
Thanks a lot for your help @Oginme!
 
Back
Top