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Old 10-14-2008, 09:43 PM   #1
jacketsdb23
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Default IBU Calcs

Hello i started a thread in beginner group and didn't get much help - so I'll try here in a slightly different manner to see if I can get some different eyes on it.

I have a porter recipe and I'm trying to calculate my IBU. The recipe says the IBU is 33.5. My calcs say about 22 and I can't figure out what I'm doing wrong.

My technique:

IBU = AAU*U*75/V

Porter recipe = 1 oz 6% AA (6 AAU) Boiled for 60 minutes
1 oz 6% AA (6 AAU) Boiled for 1 minute

The original gravity (OG) standardized value is 1.054

I estimated a U of .221 for the 60 minute hop boil
I estimated a U of .008 for the 1 minute hop boil

Total IBU = 21.6? I have a "U" chart in John Porters book.

What I haven't figured in is the 7lbs lightweight extract and the 4oz of maltodextrin. How does this figure into a IBU count? I also did a full boil, starting with 6 gallons.

Thanks for any help.

Marcel

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Old 10-14-2008, 10:01 PM   #2
scinerd3000
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1 oz 6%AA at 60 minutes==26.9IBU
1oz 6%AA at 1 minute== 4.5IBU
for a total of 31.3IBU

Keep in mind there are many ways to caluculate iBU. I use promash for my calculations and they take into account a utilization factor. Depending on if they are hops pellets, or plugs or fresh leaf hops, differing amounts of IBU's are leached into the wort. Its completly normal to come up with slightly differing numbers however a differential of 10+ ibu's in your caluclation is deffinitly wrong but i dont know where to start.

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Old 10-14-2008, 10:03 PM   #3
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All I know how to do is plug recipes into beersmith. It pretty much computes everything. I would like to figure it all out by hand, but at this point it is low on my list of things to figure out.

You can get a free trial version online. If you plan on designing beers or even keeping a recipe book this is a great way to do it. And, it is only $20, or 21, or something quite cheap for what you get.

This probably wasn't the answer you wanted so hopefully someone else can help you with the formula.

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Old 10-15-2008, 03:07 AM   #4
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this is the formula I use (From TCJOH):

IBU=weight(oz)X%AAXUtilization/VolumeX1.34

Simply put:

ozXAAXu/5X1.34
or
ozXAAXu/6.7

The variable is your Utilization. For a full boil between 1.040-1.070 I give 25% for 60 minutes. a little more than half that for 30 (13) and for 15 I give 10....The variable isnt linear so if 60=25 30 is a little higher than 12.5 and 15 is a little higher than 6.125. I just estimate and use 60=25, 30=13, 15=10, 10=5

so for your batch I get:

1X6X25/6.7=22

I wouldn't even factor in 1 minutes but maybe a few points.

It looks like they give you 30% for 60 min which is kind of high from what I've experienced and then another 7 for 1 minute:

1X6X30/6.7=26.8

+

1X6X7/6.7=6.2

=
33

I think your calculations are closer to what you'll actually get. The only way to know is to brew a few beers using whatever formula and compare the data to the actuall percieved bitterness. It's not very scientific but it works for me inso far as if I want a moderately bitter beer I use enough hops to my formula to give 35IBUs, or a really bitter beer I get +50. Compare your 35 or 50 to known commercial examples of those bitterness numbers as a litmus test.

(or just get ProMash or Beersmith but that takes the nerdiness out of the equation)

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Last edited by TeleTwanger; 10-15-2008 at 03:14 AM.
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Old 10-15-2008, 04:13 AM   #5
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Quote:
Originally Posted by TeleTwanger View Post
this is the formula I use (From TCJOH):

IBU=weight(oz)X%AAXUtilization/VolumeX1.34

Simply put:

ozXAAXu/5X1.34
or
ozXAAXu/6.7

The variable is your Utilization. For a full boil between 1.040-1.070 I give 25% for 60 minutes. a little more than half that for 30 (13) and for 15 I give 10....The variable isnt linear so if 60=25 30 is a little higher than 12.5 and 15 is a little higher than 6.125. I just estimate and use 60=25, 30=13, 15=10, 10=5

so for your batch I get:

1X6X25/6.7=22

I wouldn't even factor in 1 minutes but maybe a few points.

It looks like they give you 30% for 60 min which is kind of high from what I've experienced and then another 7 for 1 minute:

1X6X30/6.7=26.8

+

1X6X7/6.7=6.2

=
33

I think your calculations are closer to what you'll actually get. The only way to know is to brew a few beers using whatever formula and compare the data to the actuall percieved bitterness. It's not very scientific but it works for me inso far as if I want a moderately bitter beer I use enough hops to my formula to give 35IBUs, or a really bitter beer I get +50. Compare your 35 or 50 to known commercial examples of those bitterness numbers as a litmus test.

(or just get ProMash or Beersmith but that takes the nerdiness out of the equation)
Thanks! Seems there is a few different ways to calculate. I'll check out the Beersmith program. Testing IBU by drinking...but then I'd have to drink beer
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