Figuring IBUs

[lilbova3]

I use BIAB method for brewing and usually brew smaller batches than 5 gallon batch size brews. When I am figuring my IBUs for my brews I usually do it for a 5 gallon batch and then do a little additional math to figure it out for how big of a batch I want to brew.

My first ever batch I followed a clone recipe. I decided I wanted to figure my IBUs for that batch and it came out to 208 IBU. Recipe is suppose to be 90. I used this equation for calculating.
Hops in ounces x AA% x hop utilization / 7.25

I found hop utilization info from a chart online. Am I doing this right or what?

J

 

[RonPopeil]

I'm not a math brewer. Download brewtarget.

 

[masskrug]

No kidding. Why do math? Brewtarget

 

[lilbova3]

Brewtarget will figure in that I use BIAB and make smaller batches? I've never used it.

 

[RonPopeil]

Brewtarget is capable of adjusting for batch size and alpha acid content. As for BIAB I'm not sure what effect that has on hop utilization. I don't see how it would change things as long as you're doing a full boil. You'll just have to change your efficiency to real world numbers (guesstimate until you hit your actual OG). Since BIAB is all grain you can leave all your grains as mashed.

It's a bit quirky at times so play with it a bit but it's free and accurate as long as you mess around enough to dial it in (mash efficiency and yeast attenuation percentage are the main things to mess with). I don't bother with the mash calculator because I know my rig.