Hop substitution - Do you calculate your IBUs?

When doing a hop substitution, do you really do an IBU calculation to make sure you are not hurting the style?

Does it work reasonably well?

I just do a very simple calculation of the AU. So, if I'm substituting a 12% hop for a 10% hop, I'll cut the addition by 1/6th. Almost doesn't matter, if the AA% is close.

IBU Contribution (Tinseth) calculated as:

IBU = (U X AA% X W X 7490) / (V X C)

Where:
U = utilization = BF X BTF
BF = 1.65 X 0.000125^(wort gravity-1)
BTF = (1-exp(-0.04 X time mins))/4.15
AA% = decimal % alpha acids in hops used
W = weight in ounces of hops
V = gallons of wort
C = Gravity correction = 1 + [(Gboil - 1.050) / 0.2]

Add 10% IBU for pellet vs. leaf hops

From: Designing Great Beers, Ray Daniels


Do the IBU contribution calc for each hop addition, then add 'em all up.

Software is a wonderful tool for this situation. I use Beersmith but there are plenty of online calculators too.

word. promash FTW