I need to convert leaf hops to pellets measurement

[Crock_it_out]

I'm trying to convert leaf hop measurement to a pellet measure for a porter. The original hop bill is:
0.5 oz. Cascade (leaf, 7.2AA) at 60 min.
0.75 oz. Galena (leaf, 14.2AA) at 60 min.
0.75 oz Tettnang (pellet, 5.1AA) at 15 min.

What is the conversion to get the Cascade and Galena to pellet amounts...

Any help is appreciated.

 

[Bensiff]

I don't know about the conversion factor, but pellets do utilize better than leaf. I would put the recipe into a recipe calculator (tastybrew.com has a free one if you don't have a program) and see what the IBU's come out to and then rebuild the recipe with the pellet hops you have to match those IBU's. I would think the recipe should have the IBU's of that addition as more important to know for someone reading your recipe than the AA% of the hops that were originally used. But, what I said gives you a path to determine what those IBU's would be...and in reality, you don't even need to worry much about the slightly better utilization in that recipe, it probably amounts to under 5 IBU's which you wouldn't be able to taste anyways.

 

[GuldTuborg]

Maybe I'm just lazy, but I never bother with converting amounts unless there's a huge bittering charge (and even then...). If memory serves, there's something like a 10% difference in AA isomerization, which is just not worth worrying about. Unless you're dealing with hops from the same bag that you opened last week, a 10% AA difference is probably within the margin of error of what is on the bag. Anyway, that's how I rationalize this to myself.

 

[Bensiff]

I'm doing some research on HSI right now...just came across the number you would be looking for. Whole leaf utilization is 20-30% and T90 pellet is 30-40%, so you can do like GuldTuborg says and average that to a 10% and that is probably pretty accurate as I imagine the that stays pretty constant from one species to the next (ie if one has a 20% utilization in leaf form its pellet will be 90% and if one has a 30% leaf utilization its pellet would be 40%).