am making a recipe for a beer with a SG of about 1.107 my plan was to do 2 brews at the same time (with a friend) and one would be just base malt and get a 3 hour boil to caramelize the sugars and the other would have the same SG but I would use some darker malts (120L and special B) to get the caramel and roasted flavors with a 60 min boil. We were thinking at setting the IBUís between 50-60 and I made the 3 hour boil recipe first in BeerSmith set the hop amounts to reach the IBUís we desired. Once finished with the recipe I copied it and went to change the grains but first I changed the boil time from 180min to 60min and I noted the IBUís went way down. I played with all 3 bitterness calculations in beer smith and with everything equal only the boil time different (not the amount of time the hops are boiledÖsee below hop schedule same for both) I am getting huge difference in IBUís. My question is how can boiling for 2 hours before adding my hops change my IBUís or is this just a glitch in BeerSmith? Both the 60 min addition and the 15min addition changed the amount of IBUís it contributed.
Below is my hop schedule from BeerSmith:
1.50 oz Simcoe [11.90 %] (60 min)
1.00 oz Amarillo [8.20 %] (15 min)
Below is the difference in IBUís per boil time.
60 min Boil | 180 min Boil
Tenseth 52.0 IBU | 60.9 IBU
Rager 74.2 IBU | 80.2 IBU
Garetz 41.5 IBU | 44.5 IBU