My first brew has been in the primary fermenter for three and a half days (brewed Saturday night, it's now Wednesday morning). It's in a plastic bucket fermenter with an airlock. There are no bubbles coming out of the airlock, although there's a slight yeasty smell in the cupboard it's sitting in and the lid is bulging a bit. Through the translucent sides of the bucket I can see a two to three inch scum ring, but I can't tell whether that's krausen or just the remains of the foam head after aeration. I haven't opened the lid to check. The temperature in the room has been between 16c-19c.

What should I do?

  • Has the scum clogged your airlock? This has happened to me once before which caused the lid of my fermentation bucket to bulge. Also, check if that bulging has pushed open the lid to your fermentation bucket.
    – roto
    Feb 1, 2012 at 15:38

1 Answer 1


Relax. It sounds like fermentation is proceeding normally. The 3-inch scum ring is the krausen and is a sign of a healthy fermentation - a foam head wouldn't last 3 days. Your airlock is probably not air-tight so you don't see any activity. It's quite common - I've had this on a couple of brews.

Take a hydrometer reading in a couple of days, and you should see that the gravity has dropped to about 3/4 of your starting gravity, give or take a bit. You can leave it in the bucket for another week after that before bottling.

If you're really worried about it and want to do something now to be sure it's fermenting along, you can do one of two things:

  • take a gravity reading now, you'll see that it's less than your starting gravity - probably around 1.020 assuming a 1.040 beer.)
  • if you can't see clearly through the lid, open the lid a little and peek at the white foam on top - if it's got brown stuff on top, then it's krausen and not foam from airating.
  • This is why I like fermenting in carboys... besides the fact that it's cool to watch. Feb 1, 2012 at 12:24
  • Yep, Scum + yeasty smell = everything is fine.
    – GHP
    Feb 1, 2012 at 13:39
  • Thanks, chaps! I'm not sure why this is, but all the UK homebrew books/videos seem to use plastic buckets and all the US ones glass carboys. I can definitely see why you'd want to look inside!
    – user2113
    Feb 1, 2012 at 16:35
  • fwiw, I use plastic buckets too. That's all that was available in Norway. I got some PET carboys, but being only 5/6 gal they're not suitable for primary.
    – mdma
    Feb 1, 2012 at 18:38
  • I use plastic for everything, including primaries (without any secondary) as long as 4 weeks. Feb 1, 2012 at 23:26

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