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I brewed a 5-gallon batch of Frankenberry Chocolate Raspberry Stout July 20 (11 days ago) using a Scottish Ale Wyeast. The yeast was pitched at 78 degrees, everything was sanitary, I immediately placed the airlock on the plastic fermenter where it is now.

EXCEPT my husband didn't seal the lid on the primary, just had it sitting on there, closed, but not sealed. No activity in the airlock, small, white filmy bubbles.

Should I take a gravity reading? It smells very yeasty. I'm hoping it is just suspended yeast?

My last batch of this turned out great, no problem with fermentation.!I'm supposed to add raspberry puree at the 14 day mark. Didn't want the added expense if it's contaminated, though. Here is a picture:

  • Kathy, the picture URL is to a file on your local machine, and we can't see it; perhaps use a service like imgur.com to upload the picture and edit this post?
    – jsled
    Jul 31, 2014 at 20:10
  • 1
    Okay thanks, tried something else. I think it worked now.
    – Kathy
    Jul 31, 2014 at 20:17
  • If it smells "yeasty" and not "vinegary" then thats a good sign, but it is kind of early to tell. I'd proceed as normal, you're probably OK.
    – GHP
    Aug 1, 2014 at 12:06

2 Answers 2


"White filmy bubbles" don't on their own sound like biological contamination , especially after 11 days.

I would not worry too much about the lid of the bucket not being completely sealed. So long as it was basically closed, that should prevent any active organisms (flies, bugs, &c.) from getting in. Airborne bacteria and other spoiling agents can't really travel "up" and around obstructions (eg. Pasteur's swan-neck flask experiment). The lack of a solid "seal" would also explain the lack of airlock activity, as the CO₂ had alternate means of escape.

Does it smell bad? Does a (sanitary-ily retrieved) sample taste okay? Then it's probably good to go.

  • Just did a gravity reading (this is day 16) 1.020. Smells less yeasty, tastes of chocolate. Had a tiny bit of airlock activity a few days ago, so I suspect you were spot on about why there was such a lack of activity at first(lid not on tight, CO2 escaped). I was planning to add the raspberries at this point, after racking to a secondary, as much of the fermentation is complete. Good idea?
    – Kathy
    Aug 5, 2014 at 20:58
  • 1
    Sure. There's no particular need to rack to a secondary, either, unless you want to reuse your primary fermentation vessel in the mean time.
    – jsled
    Aug 6, 2014 at 11:55

It looks OK - it's quite common for bits of yeast to still be floating on the top of the beer. If you search google images for "beer pellicle", you'll see what a contamination can typically look like - it depends of course, but commonly they are a grey-white web-like filmy layer. Light-Brown foamy bubbles are krausen (yeast + brew residue foam), which typically rise up initially, then sink back down as fermentation progresses.

Leaving the lid unsealed only adds an extra risk-factor to getting infected, it's not a sure thing.

I would take a sample just before committing on the raspberry. After 11 days fermenting, the base beer should be quite close to finishing. If the beer tastes OK, it probably is OK. Obviously also check the gravity at this time.

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