My problem is that I have a 15L carboy a beer kit (Cooper's Irish Stout) that's supposed to be for 23L.
I vaguely recall reading somewhere that I should leave about 20% headspace (so I'm only brewing 12L). I'll be fermenting with Safale S-04.
Getting a larger fermenter is out of the question right now since I don't have the space (or approval of my better half).
My guess is that I shouldn't attempt to use the entire can and just make it up to 12L. I don't know if I can store the unused extract for a month before brewing it a 2nd batch. So I'm thinking of making up 12L of something that's a little more concentrated than the manufacturer's recommendation.
Has anyone done something like this? How concentrated can I make it and still have it palatable? I usually like big, heavy tasting beers.