Help with calculating the average boil gravity

[prankster1590]

I need an estimation of the average gravity during the boil when using Tinseth. I have a certain way of calculating things that seem to be a little different than the way most people seem to be calculating things, so I have often different numbers. which is strange since there is only one truth and that is the number of the actual beer.

If I for example calculate an IBU of 23 and a certain homebrewerfriend calculator calculates 21, than im a little bit worried because the calculation should be the same, so it should give the same number. I think the difference is in the calculation for the average boil gravity.

This is how I would calculate it:

I want a 20 L of wort in the Fermenter with a gravity of 1,0477.

I tap of 20 liters wort from 22 liters of wort leaving trub and hops debri. Thus I need 22 L of wort with a gravity of 1,0477

22 L * 47,7 gravity points = 1049,4 points in total

I always keep in mind 4% shrinkage because of cooling down. So 22 L/0,96 = 22,917 L. This would be, for me, the post boil volume. And this is what maybe causes the difference in my calculation compared to calculations of others. Should I take this number as post boil volume or should I use the cooled down volume of 22 L as post boil volume?

So at 22,917 the boiling is stopped altough not cooled down. The evaporation rate is about 7%/60 minutes. So If I end with 22,917 L and I have been boiling for 60 minutes than I should have started with 22,917/0,93 = 24,642 L of wort containing a total of 1049,4 gravity points. That has a gravity of: 1049,4 total points/24,642 L = 42,6 point = 1,0426

*So if i take the cooled down post boil volume of 22 L.

1049,4 points / 22 L = 47,7 = 1.0477 (Which also the Final gravity). Than the average boil volume would be

(42,6 points (24,642 L) + 47,7 points (22 L))/2 = 45,15 =1,0452


*If I take 22,917 as post boil temperature than the average boil gravity would be

1049,4 points / 22,917 L= 1.0458

(42,6 points (24,642 L) + 45,8 points (22,917 L))/2 = 1,0442 as average boil gravity


So the question is. Which average boil gravity or post boil volume should i use in Tinseth?

The one with an postboil volume of 22 L and an average boil gravity of 1,0452 or the one with a post boil volume of 22,917 L with an average boil gravity of 1,0442.

 

[BrewnWKopperKat]

Which average boil gravity or post boil volume should i use in Tinseth?

I'd use the one that provides a good estimate of the actual outcome.

eta: I replied to this topic when it was in the Beginners Beer Brewing Forum. I'm looking forward to hear what the "Brewing Software" forum has to say.

 

[prankster1590]

I guess that it's a difficult question. Anybody?

 

[marc1]

My understanding is that the IBU calculation formulas are rough estimations based on very specific conditions. I think it's good to pick one and get used to how the calculations match up with taste, then use that experience when calculating future brews.

If this is just for you then use yours and get familiar with the results.

Hopefully someone with experience making a calculator will chime in.

 

[Silver_Is_Money]

Read the 1997 dissertation titled: 'What's Your IBU?", by Michael L. Hall, Ph.D

https://t1.daumcdn.net/cfile/blog/0213E442509313A113?

 

[TheMadKing]

You have preboil gravity, and post boil gravity. Boil off is a constant rate, so it's linear. Draw a line between the two points and work out the slope. It seems to be a pretty straightforward linear function

Regarding your actual objective - someone way smarter than me will undoubtedly chime in on your methodology

AKA, Larry, Vikeman, Doug, etc..

Edit ^^Larry beat me to the punch

 

[Silver_Is_Money]

My best advice is to not treat Tinseth as if he is some sort of IBU god. His method (math model) is after all merely empirical, as based upon observation. It is highly delimited to only a certain set of rigid procedural steps and process/equipment methodologies, and certain limited forms of hops. It therefore has about as much chance of modeling "Your IBU Reality" as does any other empirical model. That is likely to be not much chance...

 

[prankster1590]

Yes thanks.

Ok should I take the gravity of the post-boil volume of 22 Liters when the wort has cooled down or the gravity of the post-boil volume of 22.917 Liters when it is still hot.

Pretty straightforward question right!?

You only have to answer HOT or Cold.

 

[Silver_Is_Money]

You have preboil gravity, and post boil gravity. Boil off is a constant rate, so it's linear. Draw a line between the two points and work out the slope. It seems to be a pretty straightforward linear function

This!

 

[Silver_Is_Money]

Cold is how I do it, but then I never consulted Tinseth as to how he did it.

 

[TheMadKing]

Yes thanks.

Ok should I take the gravity of the post-boil volume 22 Liters when the wort has cooled down or the gravity of the post-boil volume of 22.917 Liters when it is still hot.

Pretty straightforward question right!?

You only have to answer HOT or Cold.

I would match the temperature of your preboil gravity - as long as the two temperatures are similar and the level of expansion is similar your slope will be the same. So Hot is probably the best option unless you normalize both readings to the cold volume.

 

[DBhomebrew]

Yes thanks.

Ok should I take the gravity of the post-boil volume 22 Liters when the wort has cooled down or the gravity of the post-boil volume of 22.917 Liters when it is still hot.

Pretty straightforward question right!?

You only have to answer HOT or Cold.

Volumes used in formulae tend to be at room temperature, 'Cold' or a hot measurement corrected to room temp. Whether that is true for your software, I know not.

 

[Silver_Is_Money]

Kepler and Newton defined the motions of the heavens by math modeling empirical observation. And their math models were wrong. Einstein improved upon them, and there is a very strong likelihood that someday he will also be shown to have been wrong.

 

[prankster1590]

Cold is how I do it, but then I never consulted Tinseth as to how he did it.

Thank you. Yes but there is no extraction or isomerization anymore at cold temperatures. So my guess would be Hot because you get the wrong U% percentage. Because extraction is more difficult at higher gravities.

The average boiling gravity for 22 L is 1.045
And for 22,917 L it is 1.044.

So they give different U% values.

That is my doubt

 

[Silver_Is_Money]

When such doubt leads to answers of 23 IBU's vs. 21 IBU's, why fret about it? After all it is merely empirical. And there is little to choose from between an empirical based math model that results in a guess of 23 vs. a highly similar math modeled guess of 21.

 

[Silver_Is_Money]

Tinseth should be approachable.

 

[prankster1590]

When such doubt leads to answers of 23 IBU's vs. 21 IBU's, why fret about it? After all it is merely empirical. And there is little to choose from between an empirical based math model that results in a guess of 23 vs. a highly similar math modeled guess of 21.

Because I wanna clone Heineken. Perfectly.

But this is more about the theory behind the equation. The example is 23 vs 21 IBU. I believe the homebrewersfriend recipe calculator had an average boil gravity of 1.043 calculated for my example.

 

[Silver_Is_Money]

You may have to consider hop extracts.

I wonder how closely the IBU's of one lot of Heinikin analytically mirror those of another. And IBU's can drift with age....

 

[Silver_Is_Money]

Because I wanna clone Heineken. Perfectly

You will not likely find perfection in that which is merely empirical.

 

[marc1]

Because I wanna clone Heineken. Perfectly.

But this is more about the theory behind the equation. The example is 23 vs 21 IBU. I believe the homebrewersfriend recipe calculator had an average boil gravity of 1.043 calculated for my example.

At the "perfect match" level, you may need to start actually measuring IBUs to see how they match up.

You could try contacting homebrewer's friend to ask. I'm not sure how much they consider proprietary.

 

[Silver_Is_Money]

What came first, the universe, or the various and diverse math models that merely attempt to "model" it?

 

[Silver_Is_Money]

You may have to consider hop extracts.

I wonder how closely the IBU's of one lot of Heinikin analytically mirror those of another. And IBU's can drift with age....

On top of this, I wonder how just how closely the analytically derived IBU results from one lab may mirror those of another lab for the very same lot and age of beer.

 

[TheMadKing]

On top of this, I wonder how just how closely the analytically derived IBU results from one lab may mirror those of another lab for the very same lot and age of beer.

You're feeling philosophical this morning Larry

OP I agree with what he's driving at - we live in a world of imprecise perception and can never duplicate something exactly. Chasing a "perfect clone" is like spending your time trying to find two identical snowflakes. There are simply too many variables to make that an achievable goal.

What about modifying your goal to brew something that you and a panel of tasters cannot distinguish from commercial Heineken in a blind trial (the old triangle test)? That will allow you some margin of error to work within that might make your objective more achievable.

 

[prankster1590]

Ok. So what do you think approaches reality the most? The cooled down wort or the hot wort gravities for calculating the average boil Temp. Is it only the average gravity for when the wort is 100 celsius (212 Fahrenheit) or do you use the cooled down version. Since average Boiling gravity means, if you take it literal, when its boiling.

The goal of an empirical equation is to approach reality as close as possible.

Do you people take into account the shrinkage that occurs during cooling down when you calculate the water balance?

 

[BrewnWKopperKat]

In addition to "What's Your IBU?", "Tracking IBU Through the Brewing Process: The Quest for Consistency" [1] and "The IBU is a LIE! Kind of....." [2] may be of interest. BBR and Brulosophy also have podcasts/articles where they talk about measuring IBUs from "zero minute boil" recipes.

[1] Tracking IBU Through the Brewing Process: The Quest for Consistency
[2] The IBU is a LIE! Kind of..... | Experimental Homebrewing

If current or future readers find these links helpful, then my typing, proofreading and editing was "time well spent".

eta: formatting, merged my next reply into this reply.

 

[BrewnWKopperKat]

eta: merged with previous reply.

 

[Silver_Is_Money]

Ok. So what do you think approaches reality the most?

Thinking devoid of repetitive and repeatable testing is pretty much useless. Thinking with inadequate observation and testing leads to conclusions such as "Bees can't fly", or that insects have 4 legs, or that light things fall more slowly than heavy things, or that spontaneous life begins within a chunk of rotten meat or within a bag of grain or flour, or that night air is the source for a multiplicity of diseases.

Short version: I have done zero IBU testing, so my thoughts on IBU's plus about $3.50 might buy you a nice Starbucks coffee.

You are of course free to test and develop a math model for IBU's. No one will stop you. Or you can email Tinseth and ask him your question. Or ditto Michael L. Hall, Ph.D, or Christopher S. Hamilton, Ph.D.

 

[VikeMan]

The correct answer, of course, is "at whatever temperature Glenn Tinseth meaured his volumes." I don't think he's ever said in any of the articles/interviews, but I strongly suspect it was room temp. That's what I've used anyway.

You'll also have other brewhouse variables affecting your real IBUs. Which is why I built my software with a Brewhouse Hop Utilization Multiplier parameter that can be used if your subjective (or measured) results tend to be higher or lower that the basic model results. (Also an adjustable pellet hop "bonus" factor.) I know a couple of the comm'l breweries using it do use the multiplier. Glenn did stellar work, but it was all under one set of brewhouse conditions (his own).

 

[IslandLizard]

Glenn did stellar work, but it was all under one set of brewhouse conditions (his own).

Exactly!
His research was based on using whole hops, not pellets.

Also an adjustable pellet hop "bonus" factor.

Which only makes sense.

 

[VikeMan]

Exactly!
His research was based on using whole hops, not pellets.

Yes, it was. And his kettle configuration and his boil vigor.

 

[prankster1590]

I know. Its on Tinseth website

https://realbeer.com/hops/research.html

The Boil Time factor accounts for the change in utilization due to boil time:


Boil Time factor = 1 - e^(-0.04 * time in mins)
--------------------------
4.15

The numbers 1.65 and 0.000125 are empirically derived to fit my data. The number 0.04 controls the shape of the utilization vs. time curve. The factor 4.15 controls the maximum utilization value--make it smaller if your kettle utilization is higher than mine.
I'd suggest fiddling with 4.15 if necessary to match your system; only play with the other three if you like to muck around. I make no guarantees if you do.

But let me rephrase the question. How do you estimate the averaged gravity during a 60 minute boil.

 

[VikeMan]

How do you estimate the averaged gravity during a 60 minute boil.

If you know your post boil gravity, post boil volume, and boil-off volume...

(Post Boil Gravity x Post Boil Volume) + (0.5 x Boil-Off Volume)
--------------------------------------------------------------------
Post Boil Volume + (0.5 x Boil Off Volume)

The above assumes a constant boil-off rate, which may not be strictly speaking true.

Or, just averaging the pre and post boil gravities will get you pretty close.

 

[prankster1590]

If you know your post boil gravity, post boil volume, and boil-off volume...

(Post Boil Gravity x Post Boil Volume) + (0.5 x Boil-Off Volume)
--------------------------------------------------------------------
Post Boil Volume + (0.5 x Boil Off Volume)

The above assumes a constant boil-off rate, which may not be strictly speaking true.

Or, just averaging the pre and post boil gravities will get you pretty close.

Thank you. I can work with that. Im gonna try it out. I'm at work know so gonna let you know later. My first impression of this equation is that it calculates the gravity when boiling is halfway through (Gravity at 30 minutes).

 

[VikeMan]

Thank you. I can work with that. Im gonna try it out. I'm at work know so gonna let you know later. My first impression of this equation is that it calculates the gravity when boiling is halfway through (Gravity at 30 minutes).

That's exactly what it does. It's a reasonable approximation of the avg volume. You could also slice the time any number of desired times (with same intervals) and average all the volumes. But I think you'll find that it wouldn't move the needle much on the final IBU prediction. In any case, I strongly suspect that you'd be going further with avg volume computation than Glen did, so if your goal is to reproduce Tinseth as accurately as possible, you might want to be less accurate, so to speak.

 

[ScrewyBrewer]

We are keeping in mind that the ability to check the results of IBU predictions is well beyond most commercial breweries and homebrewers' budgets.

 

[BrewnWKopperKat]

Experimental Brewing has an article where they measured IBUs, Brulosophy has a couple of articles where they measured IBUs, Basic Brewing Radio has an episode (or two) where they measured IBUs from their "0 minute boil" hop sampler.

When I looked a couple of years ago, it was expensive, but not too expensive to do it "for science" that had not already been done.

Does anyone know what the current price would be for getting a bottle tested?

 

[VikeMan]

Does anyone know what the current price would be for getting a bottle tested?

$40.95 at White Labs. ASBC Beer-23A method.

 

[BrewnWKopperKat]

Thanks @VikeMan !

 

[IslandLizard]

Brulosophy has a couple of articles where they measured IBUs

Brulosophy got one of the labs (not sure which) to donate that service, they didn't pay for it themselves. They declared it clearly, which should help their cause of objectivity.
They get a lot of those kind of donations to support their exbeeriments.

 

[prankster1590]

That's exactly what it does. It's a reasonable approximation of the avg volume. You could also slice the time any number of desired times (with same intervals) and average all the volumes. But I think you'll find that it wouldn't move the needle much on the final IBU prediction. In any case, I strongly suspect that you'd be going further with avg volume computation than Glen did, so if your goal is to reproduce Tinseth as accurately as possible, you might want to be less accurate, so to speak.

So I want 22 liters of 1.0477. This is 22*47.7 = 1049.4 total gravity points

*With preboil = 24,642 L and postboil = 22 Liter the equation gives an estimation of (22 L*1.0477 + 1.321)/(22 L+1.3210 L) = 1.045
This corresponds to 22 L + 1.321 l = 23.321 L --> 1049.4 points / 23.321 L = 45 points =1.045

*With preboil = 24.642 L and postboil = 22.917 L the equation gives an estimation of (22.917 L*(1049.4 point / 23.78 L =1.0458) + 0.8625 L) /(22.917 L + 0.8625 L) = 1.044
This correspond to 24,642 L*(1-(0.07/2)) = 23.7795 L --> 1049.4 points/23.7795 L = 1.044

So longer boiling results in a higher gravity. More concentrated solution since less water.

But here it comes. WTF is this homebrewers friend calculator doing? The more water there is left the more concentrated the wort is. That BS ofcourse. Something is not good with that calculator. Or im crazy.
Does anybody knows whats happening here?