Palmer´s How to Brew "IBUs" calculations questions

I´ve been reading the section "how to measure hops " in chapter 5, pages: 54-60 and a few questions come to mind.

I have trouble understanding the section about utilization. I´ll paste the text here:

""""""""""""""""""""""""""""""""""""

Utilization
The utilization is the most important factor. This number describes the efficiency of the isomerization of the alpha acids as a function of time. This is where a lot of experimentation is being conducted to get a better idea of how much of the hops are actually being isomerized during the boil. The utilization numbers that Tinseth published are shown in Table 7. To find the utilizations for boil gravities in-between the values given, simply interpolate the value based on the numbers for the bounding gravities at the given time.

For example, to calculate the utilization for a boil gravity of 1.057 at 30 minutes, look at the utilization values for 1.050 and 1.060. These are .177 and .162, respectively. There is a difference of 15 between the two, and 7/10ths of the difference is about 11, so the adjusted utilization for 1.057 would be .177 - .011 = 0.166.

The Utilizations for 60 minutes and 15 minutes at a Boil Gravity of 1.080 are 0.176 and .087, respectively. Inserting these values into the IBU equations gives:

IBU(60) = 9.6 x .176 x 75 / 5 = 25 (rounded to nearest whole number) and
IBU(15) = 4.6 x .087 x 75 / 5 = 6
Giving a grand total of 31 IBUs.

"""""""""""""""""""""""""""""""

The main question I have is: How am I supposed to know what the boil gravity will be at minute 15, 30 or 60 or "X" when I am trying to design a beer?. If I am trying to design it from scratch (with no software help whatsoever) and want to figure out how bitter the beer will be, and find out the IBUs, how should I do it then?. If the IBUs calculation depends on the gravity of the boil, then it´s impossible to accurately (or at least a solid number) calculate the IBUs. Am I wrong?. I should be wrong, otherwise reaching a particular IBUs level would be erratic for every brewer.

Also, What is the boil gravity?. Is he meaning I need to measure the gravity of the wort while its at the 30 minute boiling time?.

Bottom line; I want to be able to set the amounts of malt (and kinds of malt), temperatures, and hops on paper. How can I calculate the IBUs (Utilization specifically) without waiting until boiling time?.

use some free brewing software

MisterTipsy said:

use some free brewing software

Click to expand...

No man, that´s the point. I want to be able to say I did all the numbers to find out how much of everything I need, and how I need to do it. I purchased Beersmith months ago. But using Beersmith is like a kid using a calculator to do his second grade homework.

Progfan2010 said:

No man, that´s the point. I want to be able to say I did all the numbers to find out how much of everything I need, and how I need to do it. I purchased Beersmith months ago. But using Beersmith is like a kid using a calculator to do his second grade homework.

Click to expand...

Interestingly enough, Palmer has been saying for several years that he was in error stating that utilization had anything to do with wort gravity. So, it's incorrect anyway you calculate it, using that formula.

That book is older, and out of date, but it's still a good resource in many ways. It's just that since about 2008, it's become mainstream to consider IBUs totally independent of wort gravity. Even Greg Tinseth has agreed with that.

Progfan2010 said:

No man, that´s the point. I want to be able to say I did all the numbers to find out how much of everything I need, and how I need to do it. I purchased Beersmith months ago. But using Beersmith is like a kid using a calculator to do his second grade homework.

Click to expand...

Pfffft...I use my home made hop abacus to calculate IBU.

MisterTipsy said:

Pfffft...I use my home made hop abacus to calculate IBU.

Click to expand...

Lol

I had no idea the hops utilization and wort gravity relationship were no longer linked. Read that chapter in Palmers book and a similar section in Mosher's Radical Brewing last week.

Where are you hearing this? The only brew news I get is the Basic Brewing podcast but can't keep up with all the episodes. Maybe I need a new news source?

maltoftheearth said:

Where are you hearing this? The only brew news I get is the Basic Brewing podcast but can't keep up with all the episodes. Maybe I need a new news source?

Click to expand...

I got it from the horse's mouth, in mid 2008 I think it was. NOT that I'm calling JP a horse- of course.

He told me he went to a conference where it was presented, and then he did his own research, and then he presented his info at the NHC. He said he "got it wrong" in the first edition of How to Brew, but did tell me that the utilization "may be impacted by break material".

After that, he did a few brewing podcasts, including Basic Brewing Radio, talking about this. I think one was a few years ago called something like "What is an IBU really?" so look for that one if you like BBR podcasts.

The interesting thing is that most experts (and I am NOT one!) agree that IBU models like Tinseth's (or Rager's) seem to sort of still have the correct IBUs, even without taking wort gravity into account. I guess that's why Palmer said that "break material may impact the IBUs".

maltoftheearth said:

Where are you hearing this? The only brew news I get is the Basic Brewing podcast but can't keep up with all the episodes. Maybe I need a new news source?

Click to expand...

I asked essentially this over at StackExchange and was pointed towards the 18 minute mark of this podcast.

Thanks Yooper and Kiss. I think it is exciting to be a part of a rapidly changing field, thanks for sharing.

Progfan2010 said:

I´ve been reading the section "how to measure hops " in chapter 5, pages: 54-60 and a few questions come to mind.

Click to expand...

I meant to tell you that during her senior year, my daughter visited Cuernavaca, and stayed with a family for a few days. She loved it, and still talks about how much she loved Cuernavaca and all of the people she met there. It was a warm friendly place, and beautiful. I think she hoped to live there someday, but it didn't work out for her.

Yooper said:

I meant to tell you that during her senior year, my daughter visited Cuernavaca, and stayed with a family for a few days. She loved it, and still talks about how much she loved Cuernavaca and all of the people she met there. It was a warm friendly place, and beautiful. I think she hoped to live there someday, but it didn't work out for her.

Click to expand...

Oh really?. I´m glad to hear that, man !!. Actually, my mother in law used to host students from the USA and I had the chance to meet most of them. Yes, I think most of them had a good time. We are still in contact with a few. They were all good, fun people. HA !, I used to brag about Mexican beer back then....I had no idea.

Unfortunately, Cuernavaca has become a bigger city with some of the typical problems a larger city acquires. Also, drug cartels seem to like it too and it´s not uncommon to read news about killings by the dozen. It´s pretty sad. Actually, there are only 2 spanish schools left in the city due to the sudden fall of demand from foreign students.

Regarding the Utilization issue. Or basically, the IBUs topic; Should I relate to Tinseth for my math?. Do you have a link that explains it clearly and in a simple way?. I´ve found some but they have confused me more than they have helped me.

Regards

Ed

Progfan2010 said:

Regarding the Utilization issue. Or basically, the IBUs topic; Should I relate to Tinseth for my math?. Do you have a link that explains it clearly and in a simple way?. I´ve found some but they have confused me more than they have helped me.

Click to expand...

Ed,
Have you read this:
http://realbeer.com/hops/research.html

It's Tinseth's formula. I use it to calculate IBU in Excel.

JiBiru8 said:

Ed,
Have you read this:
http://realbeer.com/hops/research.html

It's Tinseth's formula. I use it to calculate IBU in Excel.

Click to expand...

Yeah, seems great. I´d like to see an example though. Do you have any?

Yooper said:

The interesting thing is that most experts (and I am NOT one!) agree that IBU models like Tinseth's (or Rager's) seem to sort of still have the correct IBUs, even without taking wort gravity into account. I guess that's why Palmer said that "break material may impact the IBUs".

Click to expand...

This is what makes the "impact of wort gravity on IBU calculation" discussion mostly an academic exercise. I find it interesting, but I still use Tinseth's formula for approximating IBUs.

Choose a formula that you are comfortable applying. Use it consistently. Even if the actual figures are always technically inaccurate, you will grow accustomed to using that formula in your brewery and thus be able to make very precise, predictable recipe adjustments. I know that seems like a slight copout, but the only way to get truly accurate IBU figures is lab analysis, which is almost always very costly.

Progfan2010 said:

Yeah, seems great. I´d like to see an example though. Do you have any?

Click to expand...

Sure. Let's take Da Yooper's House Pale Ale.
https://www.homebrewtalk.com/f66/da-yoopers-house-pale-ale-100304/

Batch Size (Gallons): 5.25
Original Gravity: 1.058
IBU: 43.6

1 ounce Cascade 60 minutes
.75 ounce cascade 30 minutes
1 ounce Cascade 10 minutes
1/2 ounce cascade 5 minutes
1/2 ounce cascade flameout

1 ounce cascade (dryhop)

I used homegrown cascade for the late hopping additions, so had to guestimate the final IBUs, but used commercial pellet hops for the bittering additions (8% AAU).

-----------------

You should get 49.947 IBUs. A different value from what Yooper got, but I don't know how she calculated her IBUs, nor her guesstimates of the late hopping additions. But if you use 8% for all, you should get what I got.

I made a simple Excel spreadsheet that should be real easy to understand, but it seems I can't attach it here!

He's asking for someone to "show their work," not just plug numbers in to a spreadsheet. I'll give it a go.

Batch Size: 5.25 gallons

OG: 1.058

1.0 oz 8.0% AA Cascade, 60 minutes
* remember AA is a percentage, so use 0.08 as the decimal figure for calculations

Assume: pre-boil volume is 6.5 gallons
Pre-boil SG = 1 + (OG - 1) * (Batch size / Pre-boil volume)
Pre-boil SG = 1 + 0.058 * (5.25 / 6.5)
Pre-boil SG = 1 + 0.058 * 0.80769
Pre-boil SG = 1 + .04685
Pre-boil SG = 1.047
Assume: average SG is the midpoint of pre and post boil SG (1.053)

Boil Time factor = (1 - e^(-0.04 * time in mins)) / 4.15
Boil Time factor = (1 - e^(-0.04 * 60)) / 4.15
Boil Time factor = (1 - e^(-2.4)) / 4.15
Boil Time factor = (1 - 0.0907) / 4.15
Boil Time factor = 0.9093 / 4.15
Boil Time factor = 0.21910

Bigness factor = 1.65 * 0.000125^(wort gravity - 1)
Bigness factor = 1.65 * 0.000125^(1.053 - 1)
Bigness factor = 1.65 * 0.000125^(0.053)
Bigness factor = 1.65 * 0.62106
Bigness factor = 1.02475

decimal alpha acid utilization = Bigness factor * Boil Time factor
decimal alpha acid utilization = 1.02475 * 0.21910
decimal alpha acid utilization = 0.22453
* this utilization figure jibes with Tinseth's chart

mg/l of added alpha acids = (decimal AA rating * ozs hops * 7490) / volume of finished beer in gallons
mg/l of added alpha acids = (0.08 * 1.0 * 7490) / 5.25
mg/l of added alpha acids = (599.2) / 5.25
mg/l of added alpha acids = 114.13333

IBUs = decimal alpha acid utilization * mg/l of added alpha acids
IBUs = 0.22453 * 114.13333
IBUs = 25.6
* this figure jibes with Tinseth's online calculators

Lather, rinse, and repeat for further additions, remembering to recalculate the boil time factor for each addition at a different time in the boil. Total IBUs are the result a simple summation of the individual additions' contributions.

Yuri_Rage said:

Choose a formula that you are comfortable applying. Use it consistently. Even if the actual figures are always technically inaccurate, you will grow accustomed to using that formula in your brewery and thus be able to make very precise, predictable recipe adjustments.

Click to expand...

I agree that this is the most practical advice.

Yuri_Rage said:

This is what makes the "impact of wort gravity on IBU calculation" discussion mostly an academic exercise. I find it interesting, but I still use Tinseth's formula for approximating IBUs.

Click to expand...

I guess that was the point- even though the wort gravity isn't what impacts the ultilization, that Tinseth's formula still seems to work.

The Rager scale and Tinseth's scale do seem to differ and that's the thing to think about. In other words, pick the scale that seems "right" to you, and stick with it. I know what 40 IBUs (Tinseth) taste like in my APA. I would get a different number with Rager. And perhaps when the beer would be analyzed it would be different than both. But If you stick with one scale, and you use it for all beers, then you'll know what 25 IBUs tastes like in your beers. Does that make sense? It's not a perfect calculator, but it is the best we have at this time.

Yuri_Rage said:

He's asking for someone to "show their work," not just plug numbers in to a spreadsheet. I'll give it a go.

Batch Size: 5.25 gallons

OG: 1.058

1.0 oz 8.0% AA Cascade, 60 minutes
* remember AA is a percentage, so use 0.08 as the decimal figure for calculations

Assume: pre-boil volume is 6.5 gallons
Pre-boil SG = 1 + (OG - 1) * (Batch size / Pre-boil volume)
Pre-boil SG = 1 + 0.058 * (5.25 / 6.5)
Pre-boil SG = 1 + 0.058 * 0.80769
Pre-boil SG = 1 + .04685
Pre-boil SG = 1.047
Assume: average SG is the midpoint of pre and post boil SG (1.053)

Boil Time factor = (1 - e^(-0.04 * time in mins)) / 4.15
Boil Time factor = (1 - e^(-0.04 * 60)) / 4.15
Boil Time factor = (1 - e^(-2.4)) / 4.15
Boil Time factor = (1 - 0.0907) / 4.15
Boil Time factor = 0.9093 / 4.15
Boil Time factor = 0.21910

Bigness factor = 1.65 * 0.000125^(wort gravity - 1)
Bigness factor = 1.65 * 0.000125^(1.053 - 1)
Bigness factor = 1.65 * 0.000125^(0.053)
Bigness factor = 1.65 * 0.62106
Bigness factor = 1.02475

decimal alpha acid utilization = Bigness factor * Boil Time factor
decimal alpha acid utilization = 1.02475 * 0.21910
decimal alpha acid utilization = 0.22453
* this utilization figure jibes with Tinseth's chart

mg/l of added alpha acids = (decimal AA rating * ozs hops * 7490) / volume of finished beer in gallons
mg/l of added alpha acids = (0.08 * 1.0 * 7490) / 5.25
mg/l of added alpha acids = (599.2) / 5.25
mg/l of added alpha acids = 114.13333

IBUs = decimal alpha acid utilization * mg/l of added alpha acids
IBUs = 0.22453 * 114.13333
IBUs = 25.6
* this figure jibes with Tinseth's online calculators

Lather, rinse, and repeat for further additions, remembering to recalculate the boil time factor for each addition at a different time in the boil. Total IBUs are the result a simple summation of the individual additions' contributions.

Click to expand...

Awesome !!!. Thank you very much for your time and effort. If it works for you, I´ll just do it the same way.

Just one question. The "S" on SG stands for what?. ...

Specific gravity - technically what we're measuring when we measure OG and FG.

Just for academic purposes, if the SG of the boil has no effect on hop utilization, than is there any issue with newbies using a partial boil to make IPA's in terms of bitterness? Or is there anything I'm forgetting about outside of greater cararmelization?