Calculating IBU's

[seamusfm]

Hi,
I'm brewing a Brewers Best Australian IPA extract kit. The kit instructions indicate an IBU of 64-68. I put the recipe into iBrewmaster and it calculates an IBU of just over 31. I'm wondering if I maybe entered the recipe wrong? Or the software calculated incorrectly? Recipe follows, as entered in iBrewmaster.

Brewers Best australian IPA

OG: 1.054
Type: Extract
FG: 1.013
ABV: 5.37 %
Calories: 176 IBU's: 31.23
Efficiency: 70 % Boil Size: 2.50 Gal
Color: 10.0 SRM Batch Size: 5.00 Gal
Preboil OG: 1.113 Boil Time: 60 minutes


Grains & Adjuncts
Amount Percentage Name Time Gravity
2.50 lbs 32.05 % Amber Dry Extract 60 mins 1.044
3.30 lbs 42.31 % Briess Golden Light LME 60 mins 1.038
1.00 lbs 12.82 % Briess Caramel 30L 60 mins 1.034
8.00 ozs 6.41 % Briess Munich 10L 60 mins 1.035
0.50 lbs 6.41 % Briess Carapils 60 mins 1.034

Hops
Amount IBU's Name Time AA %
1.00 ozs 10.76 Cascade 60 mins 5.50
1.00 ozs 15.40 Galaxy 20 mins 13.00
1.00 ozs 5.07 Galaxy 5 mins 13.00
1.00 ozs 0.00 Galaxy 0 mins 13.00

Yeasts
Amount Name Laboratory / ID
1.0 pkg Safale US-05 Fermentis US-05

Additions
(none)

 

[theveganbrewer]

Looks like your software is busted. I'm getting 64 IBUs on Beersmith for this recipe.

 

[ChessRockwell]

Looks like your software is busted. I'm getting 64 IBUs on Beersmith for this recipe.

I think the software is about right (I'm getting like 36ibu's) - did you account for the 2.5 gallon boil size?

If you want more IBU's you're going to have to either do a full boil (or closer to it), or switch around some of the higher alpha hops to earlier in the boil instead of using lower alpha cascades for the main bittering.

 

[beergolf]

The other option is to add the LME at flameout. That will get the IBU's up.

 

[theveganbrewer]

Oh, this is an extract. nevermind.

 

[beergolf]

Oh, this is an extract. nevermind.

partial boil, extract kit. Top off water is added to make the final volume.

I did a Brewers Best kit for my first brew and if I remember correctly the LME was added late in the boil. If you change that in the brew software it changes the hop utilization.

 

[logan3825]

Try using Beer Calculus.

 

[seamusfm]

partial boil, extract kit. Top off water is added to make the final volume.

I did a Brewers Best kit for my first brew and if I remember correctly the LME was added late in the boil. If you change that in the brew software it changes the hop utilization.

The recipe calls for adding all extracts at the beginning of boil.
It also calls for a 2.5 gallon boil. But if I change the iBrewmaster to 5.0 gal boil, it gives me 63.5 IBU.
Beer calculus gives about the same.
So it looks like the kit calculated the IBU based on a full boil, but the instructions say a 2.5 gallon boil.

 

[helibrewer]

The recipe calls for adding all extracts at the beginning of boil.
It also calls for a 2.5 gallon boil. But if I change the iBrewmaster to 5.0 gal boil, it gives me 63.5 IBU.
Beer calculus gives about the same.
So it looks like the kit calculated the IBU based on a full boil, but the instructions say a 2.5 gallon boil.

The kits IBU's should always be based on the final volume, not the boil amount. They should be adjusting their hop amounts for the partial boil. In reality I don't think it makes a ton of difference, I have read that human taste caanot differentiate single IBU's, it's closer to 5 IBU's for taste threshold.

 

[ChessRockwell]

They should be adjusting their hop amounts for the partial boil. In reality I don't think it makes a ton of difference, I have read that human taste caanot differentiate single IBU's, it's closer to 5 IBU's for taste threshold.

They should be, but at least a couple of the Brewer's Best kits I've done really don't. I remember running into this problem before. They seem to calculate the IBU's they advertise based on a full boil and then tell you explicitly in the instructions to boil "2.5 gallons or more". A 2.5 gallon boil vs. a 5 gallon boil with the same extract + hops I think would be quite noticeable, like close to 1/2 the IBU's, not some indistinguishable threshold 5 ibu difference.