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Hop Biterness

Grimsbylad

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Although I am new to BS3 I have been brewing for many years. I have just downloaded the trial version.I am enjoying it very much and will buy it. There does seem to be an error in the IBU

calculations however. In the design part I entered 1 oz of centennial hops @ 8.7% for 60 mins. This calculated to be 17.3 IBU'S  This seemed low so I used the hop bitterness tool and using the same

batch vol, boil vol and boil gravity I got an IBU of 28.1 IBU which I think is more accurate.  The IBU's for later hop additions of citra and mosaic @ 20 mins where almost exactly the same

: 15.8 IBU design  /  15.6 IBU Hop biternesss. As I said I am new so this could be something I am doing wrong but I can't see where.
 

Oginme

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I just tested making a recipe with 14 grams of Centennial at 10% AA in a recipe with a boil gravity of 1.036 and an ending gravity of 1.048.  This gave me an estimated IBU value of 36.6.

Next I took the IBU tool and input the same hops at the same %AA and same quantity.  I entered the batch size at 10 liters, boil at 14.75 liters and the boil gravity of 1.036. This gave me a predicted IBU level of 40.1. 

The issue is that the tool does not distinguish between boil off (concentration) and trub loss (true volume loss).  In my process, I boil off 3.75 liters and end up at 11 liters post boil, transferring 10 liters to the carboy. When I set the batch size for my end of boil volume of 11 liters, the predicted value corrected to 36.5 IBU.  Given rounding errors, this pretty much matches the prediction in the design tab.

Are you adding any top off water to the fermenter?  Is your trub and chiller loss very high?  Check with the correction of post boil volume instead of batch size and see what that does.  If that does not change things to bring the answers close, then export the recipe as a .bsmx file and post it in this thread so we can take a closer look at what is going on.
 

Grimsbylad

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Here is the recipe I am using to check IBU's .
I have my boil off at 1.25 gals/hr and trub loss at 1 gal. this means I have  6.5 gals in the kettle with 5.5 gals  going into the fermentor.

1oz of 8.7% for 60 mins should give an IBU of about 28 IBU in this recipe but only reports 17.6

Using bitterness tool I set batch volume to 6.5 gals,Boil vol to 8.02 and boll gravity to 1.055 which gave me 24.2 which is probably correct.

As I said before I am new to BS3 and quite possibly  missing something but I can't figure out what, especially when the late addition hops seem to be correct.

Thanks for your input Tony
 

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Oginme

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OK, figured it out.  The bitterness tool does not take into account your elevation.  You have your elevation set in your equipment profile to 5280 ft, which affects the temperature of your boil and the rate of isomerization of the alpha acids.  When I set the elevation to 0, the IBU tool came fairly close (24.2 vs 24.9) to the recipe. 
 

Grimsbylad

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Thanks very much for your help, you have made a subscriber out of me.  Tony
 

jtoots

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Oginme said:
OK, figured it out.  The bitterness tool does not take into account your elevation.  You have your elevation set in your equipment profile to 5280 ft, which affects the temperature of your boil and the rate of isomerization of the alpha acids.  When I set the elevation to 0, the IBU tool came fairly close (24.2 vs 24.9) to the recipe.

This guy is GOOD!!!!! WOW! Nice work Oginme!
 
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