IBU calculation

[homoeccentricus]

Hi folks, new on this forum. I'm considering switching from Beersmith to BF, but I have a problem with IBU calculations. For a given recipe, BS gives me 16 IBUs, but BF gives me 25 IBUs. Both programs use Tinseth. When I calculate the IBUs on http://www.brewersfriend.com/ibu-calculator/ I do get the same IBUs as BS. Any ideas why that may be?

 

[Thurston Brewer]

Not clear... What's the difference between 'BF' which gives you 25 and 'brewersfriend.com/ibu-calculator' which gives you 'the same IBUs as BS'. BF is not the same as 'brewersfriend.com/ibu-calculator'?

 

[homoeccentricus]

When I built the recipe in Brewer's Friend I got 25 IBU, but when I simply used the calculator I got a different result: 16 IBU. So the recipe builder calculates things differently. So either there's a setting I don't know of, or there's a bug in the recipe builder. I'm pretty sure the 16 IBUs is correct, since that is what I get in Beersmith and another program.

 

[Thurston Brewer]

OK, Gotcha. The only thing I've noticed is the difference that boiling time makes to IBU contribution. If there's a difference in the way that's entered in the two different locations that could explain it. I use the BF Windows application. If you post your recipe I could try it there and see what the result it.

 

[homoeccentricus]

OK, Gotcha. The only thing I've noticed is the difference that boiling time makes to IBU contribution. If there's a difference in the way that's entered in the two different locations that could explain it. I use the BF Windows application. If you post your recipe I could try it there and see what the result it.

Here is the recipe. AFAIK it's a 75 minute boil in all the programs I've tried...

http://www.brewersfriend.com/homebrew/recipe/view/410106/roche-four-lodo

 

[Thurston Brewer]

Total boil is 75 minutes, but the boil times of each hop addition is the key to the IBU calculation. That and the specifics of the grain bill. Here's what I got:

26.1 is prettly close to the 25.8 listed in the recipe builder. I'd go with that.

In the IBU Calculator:

This varies slightly depending on what form of hops you select, but still way above 16. I don't see a big discrepancy here...

 

[jmcnamara]

Noticed 2 of the hop additions are whole leaf in the calculator but pellet in the app. that might throw it off a little bit too

 

[nzbrew]

I have just taken a recipe from BS, and manually entered it into BF, they both match up pretty close :

http://www.brewersfriend.com/homebrew/recipe/view/415809/tuatara-apa-clone = 55 IBU
same recipe in BS = 51.7 IBU

Using the BF calculator and came out at 51.83 - almost exactly the same as BS....... There must be a difference in the recipe builder calculation and the site calculator.

 

[homoeccentricus]

BTW, the est. boil size should be 16 liter, not 18 liter.

The problem may have to do with the selection of the batch size. I had 10 liters into fermentor. But I currently have a four liter kettle loss in addition to a 2 liter boil-off. I think when one chooses batch size into fermentor, the kettle loss is not taken into account, and the program treats it as if it is boil-off. When I choose 14 liters batch size in the kettle, the IBUs are more or less what I would expect. So:
boil size: 16 liter, 2 liter boil-off, 4 liter kettle loss
batch size into fermentor: 10 liter -> 25 IBU
batch size into fermentor: 14 liter -> 17.8 IBU
batch size into fermentor: 14 liter -> 17.8 IBU

For comparison, Beersmith: 16 IBUs.