Fermentation vessel too small for beer kit

Question

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.

Answer 1

It's ok to have less than 20% headspace, you just risk a blowout, meaning it could overflow and make a mess. To counter this problem use a blowoff tube and bucket:

Answer 2

Having 20% headspace is a good idea, but not necessary as HourOfTheBeast pointed out.

It's perfectly fine to make a concentrated wort. I'd recommend pitching twice the amount of yeast to ensure fermentation goes well. The main concern here is making more alcohol by volume than the yeast can handle. S-04 should handle 10% and you'll probably only be making about 8.5%.

Irish stouts are generally roasty, dry affairs. The coffee flavours in your beer will be more pronounced and there may not be a lot of sweetness to balance.

Something you could consider is fermenting the concentrated wort and diluting at bottling time. If you use a 19L bottling bucket you could take your 12L of fermented beer and add ~6.5L of boiled water (along with your priming sugar) to make the full 19L of finished beer. Should come out a little more balanced.

Answer 3

Simple rule: 23L for a 30L vessel. Scale appropriately.

This allows enough room for the head / krausen to form and not overflow (most of the time).

Answer 4

Some kit brewers (including me when I was kit brewing) successfully use the "twocan" method. Two cans, water, and yeast. No sugar, dextrose, corn syrup, light dry malt, etc. As an experiment, I would use the full can, top up with hot/cold water to 13 litres, pitch yeast when wort is at the correct temperature, seal and wait. My experience with several other Cooper's kits suggests you will be pleasantly surprised.