BeerSmith - IBUs for late additions/hopstands

[BKBrews]

Long time user of Beersmith myself, but have just come across an unusual issue.

I had hop additions at 5min and 0min, and then had a hopstand @ 80c for 20min. The issue is that BeerSmith calculates the boil hop additions in line with what you enter for the whirlpool (above 85c) timing and then assumes immediate chilling and transfer. If you then add hopstand hops, it does not then recalculate your boil hops to factor in the additional hopstand time.

Has anyone else come across this issue/thought about how to counteract it? It makes a huge difference in the numbers, which I understand isn't an issue as long as it's replicable and ends up where I want it, but it would be good to work out for future reference.

Quick example:

Whirlpool set to 6min above 85c (took 6min to chill to 85c, then only a few min to drop further to 80c):
30g Mosaic @ 5min = 10.8 IBU
20g Citra @ 5min = 8.8 IBU
20g Galaxy @ 0min = 7.6 IBU
Total = 27.2 IBU from boil hops

If I then add the following hops @ 80c for 20min:
20g Mosaic = 2.8 IBU
30g Citra = 5.2 IBU
30g Galaxy = 6.9 IBU
Total = 14.9 IBU from hopstand hops

When I added the hopstand hops in beersmith, no additional IBUs were added to the 5min and 0min additions. Total IBUs calculated in beersmith = 42.1 IBU.

To get around this, I ended up adding the boil hops above again in the software as hopstand hops @ 80c for 20min:
30g Mosaic = 4.2 IBU
20g Citra = 3.5 IBU
20g Galaxy = 4.6 IBU
Total = 12.3 IBU

New total IBU = 54.4 IBU

Sweet wort tasted really good, so will be interesting to see where it ends up. I don't particularly care like I said, but I just thought I'd see if anyone else has put though into it.

 

[yankinoz]

For best results you may need to do hand calculations from a reliable graph on alpha-isomerisation. I've done many hop stands, often using Mosaic and Galaxy, and offhand those Beersmith numbers look too high. Maybe you can report back on how it works out in comparison with a beer of known IBUs?

 

[BKBrews]

For best results you may need to do hand calculations from a reliable graph on alpha-isomerisation. I've done many hop stands, often using Mosaic and Galaxy, and offhand those Beersmith numbers look too high. Maybe you can report back on how it works out in comparison with a beer of known IBUs?

will definitely need to find something similar.

The Citra is 13.5% AA and the Galaxy is 18% AA, so that probably bumped it up a little too. The beer is a 1.067 Imperial Indian Pils pitched directly on to the WLP802 yeast cake from my previous Czech Pils, so my water is quite soft for this one too (used RO and kept minerals mainly under 50ppm across the board).