When modifying a recipe, should you scale hops based on alpha acids?

Question

I am planning on brewing several versions of an IPA where I keep the grain bill the same, and just change out the hops. I will use a single hop for each batch. The idea is to learn the aroma and flavor contributions for some common hop varieties.

I found an IPA recipe that I like, and its hop schedule is:

• 1 oz Horizon (13% AA) @ 60 min
• 1 oz Centennial (9% AA) @ 10 min
• 1 oz Simcoe (12 %AA) @ 5 min
• 1 oz Amarillo (9% AA) @ 0 min

For my first batch, I'll be trying Cascade. The labeling on the package indicates that it is 6% AA. If I scale by %AA, I end up with the following hop schedule.

• 2.2 oz Cascade (6% AA) @ 60 min
• 1.5 oz Cascade (6% AA) @ 10 min
• 2.0 oz Cascade (6% AA) @ 5 min
• 1.5 oz Cascade (6% AA) @ 0 min

Is this the best way to adjust for the different hop varieties, or is there a better way?

Answer 1

Maybe it's a typo in your question, but your boil times changed with the Cascade version of the recipe -- all additions are boiled for 60 minutes.

Provided you keep the boil times for each addition the same as the original recipe, then, yes, your approach is a good one. In the substituted hop, change the amount so that the total alpha acid contribution remains the same.

Make sure to go by the AA% for the hops that you buy, not what's quoted elsewhere. AA% change from harvest to harvest.