I have the following recipe on beercalculus:
beercalculus (along with most IBU calculators), ask for both a target batch size (which for me is 5 gallons), and a boil size. I'm not sure what to put in for the boil size, because I do a partial boil of 2 gallons (I'm brewing with extract), then mix with water to bring the batch size up to 5 gallons. The boil size has a big effect on the final IBU's, so I'm trying to determine 2 things:
- For partial boils, what would I put into one of these calculator for boil size?
- Why does the boil size effect the IBUs? I would have thought only the final batch size would matter, because the same amount of alpha acids are being dissolved regardless.
Thanks in advance!