help a newbie with a beer calculator question

[michaelpeach76]

I'm brewing a 5 gallon batch and put a recipe for an ale into my brew calculator and the IBU was 39. I'm brewing an American Amber so that's fine. Well I went back to the beginning and realized my boil volume and batch volume were both set at the default of 5 gallons on each. When I changed the boil volume to 2.5 gallons - which is what I'm boiling for a 5 gallon batch... the IBU went way down to 23. Sorry bear with me, I'm new. Question is: When I start putting my recipe together should it all be based on....in my case 5 gallon batch/2.5 boil volumes?

 

[aomagman78]

Ya. Your IBU's are more or less inversely proportional to the gravity of the water. So if in your boil you have 5gallons worth of sugar in 2.5 gallons of water, you're going to get almost 2x less hops utilization. So you'll need additional hops to reach the desired bitterness. The other thing you can do, if this is extract, is a late addition. If you just boil your water with little to none of your extract added until 10-15min from the end, you will get somewhat higher utilization during the first 45min. Not quite the same as if you were boiling 5 gallons, but at least better.

So to answer your question, always take boil volume into account - that's why it's there.

This is reproduced information, hopefully I didn't make any glaring mistakes.

 

[BBL_Brewer]

When you do partial boils, the boil gravity is higher and you get less utilization from the hops. You will have to use more hops to get the same IBU's. No way around it. That's why full volume boils are more beneficial. You use less hops and you don't have to worry about top off water. Just adjust your hops in the calculator to get your target IBU's.

 

[michaelpeach76]

Ah... makes perfect sense. Thanks for the feedback, appreciate the help.