Originally Posted by grittanomyces
I have no clue how much will be boiled off
The biabacus calculator from biabrewer.info is complex, but it will let you put in the dimensions of your kettle and give you an estimated boil off. That forum has user restrictions when you first register. You have to post an intro message before it turns on some privileges. I think downloading the calculator is one of the things you can't do until you do that first post.
- the intensity and length of the boil will effect it. So will the surface area of your pot.
- a slow boil is all you need as long as the water is circulating (or so I've read)
- my pot is undersized, so I use a slow boil to reduce boil off.
I boil off about a gallon when making a 5 gallon batch (20%), so for your 128 ounce batch I would expect a minimum of 25 oz of boil off or about 3 cups. I suspect a roiling boil might be twice that.