I’ve decided to scale down my brewing volume from 5 gallons to 2.5 gallons (the reason for this is my body can’t take the heavy lifting anymore, and 2.5 gallons seems like an easy conversion from 5). My reasoning is that I can just halve everything, but I’m concerned about hop additions. Can I just halve the AAU’s of the recipe? Am I not considering things correctly? Thanks for any input.
Re:hop additions I recommend an app like Beersmith, Brewfather, or Brewer’s Friend.
I brew 3 gallon batches to get 2.5 gallons into the keg. If you were brewing 6 to get 5 into the keg then cutting hops in half is fine. But if you’re brewing 5.5 gallons to get 5 in the keg then halving the hop additions is slightly off. If you use a recipe app you can just design your recipe for the volumes you are using.
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The short, simple answer is: yes, just divide everything in half.
All the available brewing software packages will scale recipes for you. But I have definitely ordered “5-gallon” kits and just cut them in half to make 2.5 gallon batches (ok technically I do 10-liter batches).
But! you’ll have to do some test batches to recalculate your boil-off rate, kettle loss, fermented loss, etc. in my experience, these will change significantly when you switch to a smaller boil volume, different kettle size/shape, etc.
Also, hop utilization is unique to your hardware setup, too. So calculated IBUs are really just an index to help you be consistent.
+1. It took me several batches to nail this down.