Trying to scale recipe

[spbrhs07]

I like to do 1 gallon mini batches to experiment with new recipes. I assumed it would be easy to scale up once I got it right. I use brewers friend to create my recipes and they also have a scale feature so I don't have to do the math.

I made this starting with 2 gallons at the beginning of a 90 minute boil ending with just under 1 gallon going into the fermentor. Turned out absolutely fantastic. I need 5 gallons of this beer!

View attachment ImageUploadedByHome Brew1444881414.767407.jpg

I go to scale the recipe and everything is multiplied by 5 so it looks good. Shows 5 gallons for fermentor volume and 6 gallons boil volume. However, my IBUs went from 134 to 91...

View attachment ImageUploadedByHome Brew1444881849.656679.jpg

Why does it do this and how can I fix it?

 

[btbnl]

The one thing that doesn't scale is the starting volume - 2G & 6G - and the extra water (relatively) in the first case allows for more alpha acid isomerization.