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Old 08-08-2012, 10:05 PM   #1
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Default Palmerīs 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?.

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Old 08-08-2012, 10:07 PM   #2
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use some free brewing software

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Old 08-08-2012, 11:02 PM   #3
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Originally Posted by MisterTipsy View Post
use some free brewing software
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.
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Old 08-08-2012, 11:20 PM   #4
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Originally Posted by Progfan2010 View Post
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.
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.
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Old 08-08-2012, 11:49 PM   #5
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Originally Posted by Progfan2010 View Post
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.

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

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Old 08-09-2012, 12:21 AM   #6
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Quote:
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Pfffft...I use my home made hop abacus to calculate IBU.
Lol
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Old 08-09-2012, 12:43 AM   #7
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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?

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Old 08-09-2012, 01:42 AM   #8
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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?
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".
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Old 08-09-2012, 02:23 AM   #9
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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?
I asked essentially this over at StackExchange and was pointed towards the 18 minute mark of this podcast.
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Old 08-09-2012, 02:29 AM   #10
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Thanks Yooper and Kiss. I think it is exciting to be a part of a rapidly changing field, thanks for sharing.

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