Possible contamination

This is my first all-grain batch and unfortunately it has developed some kind of growth. It didn't smell like death, actually smelled pretty good, and the samples I have been taking have all tasted good, so I went ahead and bottled it. Just curious what it could be and if I will be looking at a loss with this one.

  • Well after spending some time in the bottle, tasted one and it was terrible. Very harsh alcohol, more like nail polish. I ended up dumping, but in hind sight I wish I would have kept some of the bottles and aged them, just to see what would have happened. Oh well you live and you learn. Feb 24, 2011 at 23:17

5 Answers 5


White Film on Beer in Carboy

White film or flakes on top of beer is fairly common. It often happens in secondary, or in primary after the krausen falls.

Don't worry - your beer is probably fine!

Usually, this is the result of yeast colonies being carried to the top of the beer from the trub or yeast cake by CO2, although in some cases, it can be a sign of a bacterial or wild yeast contamination.

Take a sample of the beer. Swirl it in a glass and see if it smells funky or infected. If you can't smell anything unusual, give it a taste. Does the beer taste sour?

If not, you just have rogue colonies of yeast on your beer. They may persist until you rack the beer, but should settle upon racking, and will not affect the smell, taste, or appearance of your final carbonated beer.

If the beer does smell/taste sour, then unfortunately, your beer has become infected. You'll probably have to scrap the batch. Scrub all equipment thoroughly with cleaner, and sanitize carefully before brewing again. If you ferment in a plastic bucket, ensure there are no scratches in the plastic, as they may harbor bugs. If there are scratches, replace the vessel.

  • It didn't smell funky or taste off, actually tasted good, so I bottled it. Now time will tell. Nov 25, 2010 at 4:03
  • @beerrepository How did it turn out? I have a batch with a similar look to yours. May 18, 2014 at 21:34
  • If I remember correctly it didn't taste right. It wasn't rancid but I am guessing it had other problems like possible oxidation. May 19, 2014 at 0:45
  • -1 for "you'll probably have to scratch the batch". In my experience, 7/10 unintentional sours are very drinkable unless you have some aversion to sour beer.
    – Wyrmwood
    Nov 16, 2016 at 5:26

If it smells good, and tastes good it may not be a contamination.

However, that looks like a little mold of some sort. Not the kind that will kill you or make you blind. Best advice is to drink the beer before the contamination takes over.


Don't panic. Taste the beer. If it tastes like beer, it's probably ok. If it doesn't taste like beer, but not bad, you can do a couple of things. ONE: do nothing, bottle it, and wait to see how it matures. TWO: drop 2-3 campden tablets to sterilize the beer, then prime and bottle. THREE: Pasteurize, then add a little more malt and repitch with some fresh yeast, continue as if it were a new batch. Think about what you do and enjoy your brews. Cheers.


That doesn't look like cause for alarm to me. Give it another whiff if they start growing hairs or turn black/green. I don't think you're gonna take a loss.

The beer has great color otherwise, btw.


It looks like mold to me. I would throw it out, unfortunately.

  • 5
    It's best to confirm that it's mold before wasting a batch of beer.
    – Brandon
    Nov 23, 2010 at 21:57
  • Even if it is mold, don't automatically throw it out, you might have a delish sour brown ale. I say throw the mold out and give that beer a taste.
    – PMV
    Nov 24, 2010 at 15:52
  • 1
    I just wouldnt want anyone to get sick. You are welcome to serve contaminated beer. Its just my opinion.
    – KRock
    Nov 24, 2010 at 20:52
  • If it smells anything like beer, or even if it smells like vinegar, then it won't get anyone sick. There are very, very few known pathogens that can survive in the acidic & alocoholic(sp?) environment that exists in beer/vinegar. Its kind of the whole point we started making beer. Well, the beer goggles help by increasing population too, but I digress :)
    – GHP
    Jun 27, 2011 at 16:07

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