I was given a 48 quart brew pot . What would be a good size fermentation tank to get?
Depends how much & how your going to brew. But that size should allow a 3-5gallon (based on grain bill) BIAB.
48 quarts is 12 gallons.
are you doing extract batches, brew in a bag, or all grain with a separate mash tun?
With a kettle that size, you could do up to 10 gallon batches. I’d get a couple 6 gallon fermenters. Or a 6 and a 5 gallon
As stated above, that depends on what brewing method you plan to use. 12 gallon pot will allow you to do a full boil for a 10 gallon batch, but it would be pretty tight. You’d have to watch it like a hawk to prevent boil-overs. Keep it 8 gallons or less and you avoid that problem.
If you are brewing extract and doing concentrated boils, you could make up 15 gallon batches without a problem.
I’d recommend getting a regular brew bucket for a fermenter. Cheap, perfect size for use with 5 gallon kits, easy to move around and you can always buy a second one if you want to make bigger batches.