Beersmith IBU calc question

I've got a question involving Beersmith's IBU calculation during a partial boil brew.

When I add hops the IBU amounts for the hops don't match the calculated IBU.

For example of my hops amount are 10, 5, and 5 by hand its 20, but in beersmith it will calculate it as a higher amount like 25.

which if these numbers should I assume is correct, and *why* does the partial boil do this?

I do know that the gravity of the wort affects the hop utilization and a partial boil would obviously have a higher gravity than a full boil. I'm sorry if you already knew this and I misunderstood your question.

fenixwb said:

I've got a question involving Beersmith's IBU calculation during a partial boil brew.

When I add hops the IBU amounts for the hops don't match the calculated IBU.

For example of my hops amount are 10, 5, and 5 by hand its 20, but in beersmith it will calculate it as a higher amount like 25.

which if these numbers should I assume is correct, and *why* does the partial boil do this?

Click to expand...

kedash said:

I do know that the gravity of the wort affects the hop utilization and a partial boil would obviously have a higher gravity than a full boil. I'm sorry if you already knew this and I misunderstood your question.

Click to expand...

I understand the partial boil makes a difference as well at a late malt addition. My question is specifically in Beersmith if I add up the IBU's of the individual hop additions the total IBU number is lower than the number that Beersmith calculates and displays in the bottom portion of the program. Where are these extra IBU points coming from?

fenixwb said:

I understand the partial boil makes a difference as well at a late malt addition. My question is specifically in Beersmith if I add up the IBU's of the individual hop additions the total IBU number is lower than the number that Beersmith calculates and displays in the bottom portion of the program. Where are these extra IBU points coming from?

Click to expand...

Ahh, nevermind I figured it out. The individual IBU for each addition doesn't take into account the change in utilization with using a late malt addition.

I am confused about your question and your resolution, but if you figured it out, great! Just curious though, I assume that when you said "hops amount are 10, 5, and 5 by hand its 20"...you mean IBUs. I have actually been having some issues with IBU calculations in Beersmith as well but it looks like you are having the opposite issue, or at the very least is unrelated. (If you have something other than beersmith).

However, Beersmith will infact take late extract additions into account when calculating utilization/IBUs. In fact, that is exactly what I did for my last brew in order to increase my IBUs up to within the styles range.

I don't mean to confuse you more but I just wanted to pass that along. I wish I could actually see the calculations Beersmith is making but regardless, it definitely accounts for changes in boil gravity with late malt additions.