If I keep my fermenting beer in my living room, should I cover it with blankets or otherwise keep it out of the light? I've seen topics on brewing referencing this, but most just settle for "why take the chance?"

I'm hoping for a little more clarity on the matter.

  • I recently fermented a belgian golden strong ale on my kitchen counter top. Out of direct light, and I live in Seattle so not much direct sunlight to speak of in the winter anyway. But it turned out great. Seems that hops are the killer skunking agent. So does it then hold that in less hoppy/minimal hoppy beers this would be less of an issue? Mar 13, 2012 at 20:18
  • @ChrisPlaisier depends on how sensitive ones palate is to skunked alpha acids.
    – brewchez
    Mar 13, 2012 at 22:52
  • 1
    Though it is true that the effect comes from hops. Reference Apr 10, 2012 at 7:16
  • What is your fermenting vessel? A glass carboy or a plastic bucket?
    – Robert
    Nov 16, 2016 at 23:34

7 Answers 7


Keep it out of the light.

ESPECIALLY if the fermentation vessel is clear, but generally, keep it out of the light.

Light (specifically, UV rays) will skunk the beer, producing off-flavors. It's probably better if you have a closet or someplace else out of the way that's dark to ferment.

But - keep it out of the light.

  • 18
    and never feed it after midnight
    – mdma
    Mar 13, 2012 at 19:11
  • 3
    Well yeast DO multiple when you get them wet (with sugar water) :)
    – Graham
    Mar 14, 2012 at 13:15
  • 1
    UV isn't the main culprit, it's the visible spectrum. Keep beer out of all light at all times, only to see light at serving. Even artificial light. You'll notice an excellent vendor will never have an open top shelf of craft beer, and will keep them out of direct florescent lights. Jan 23, 2016 at 3:23

I live close to Seattle (puyallup) and we get UV rays even when its cloudy. you could through a pillow case over it but that wont block all the UV's maybe a open top cardboard box (assuming you want easy access).

Ultraviolet light is often used to purify water because it kills bacteria. Yeast Is a fungus which essentially is a slightly more complicated organism, therefore it has a little more fighting power against it's enemies (UV). Yeast stress is of coarse a big issue in fermentation and anything you can do to keep them yeasties calm the better, UV stresses yeast.

Typical commercial "beer skunking" has nothing to do with yeast, It's more of a hop alfa acid thing... here is a great link http://www.washingtonpost.com/wp-dyn/content/article/2007/02/27/AR2007022700312.html


I'm just down I-5 in Portland. I tend to use carboys for my fermentation vessels, so what I do is keep the box the carboy came in, cut a small hole in the bottom of the box, cut the top flaps off the box and make a sort of carboy sleeve that slips right back over the bottle and leaves the airlock sticking up from the small hole, so far it's worked fantastic.

  • 2
    You answered the "how", not the "why".
    – Flyhard
    Jan 22, 2013 at 8:43

It's the hops that create that skunky aroma. The UV rays react with the hop oils and spoil. Also, if the fermentor is in direct sunlight, one would assume that the fermentations temperature would begin to rise until the sun sets, when the ferm temp would start to fall! Better to keep a constant temperature and keep out of the sun.

At the very least, cover with a blanket to protect your hops!


You can wrap the whole fermentation carboy or bucket in a black plastic trash bag. It stops light and will contain any messy spills or explosions. Be sure to leave the bag open at the top so heat and gas can escape.


my 2 homebrew fermenters were getting about 30 to 40 minutes of direct sunlight at about 10 am every morning for about 6 to 7 days and the beer tastes terrible. I am now covering up my fermenters a will see how the next batch tastes.


UV wavelengths do not penetrate glass. It is more likely that visible wavelengths catalyze photodegrading reactions of the dissolved organic carbon, the stuff leaching out of the hops included.

  • 1
    Not that UV doesn't penetrate glass, most UV is blocked by clear glass. But it's the visible spectrums that do the most harm blue being the worst. Light reacts to the alpha-acids making thiol (full sulfer name escapes me) which is basically the same chemical in skunk spray. Why most beers are in Brown bottles. Those that are in clear like many American lagers don't skunk because they use a tetra hop extract that doesn't have reactions to light. Keep your beer out of light at all times. Even artificial light. Jan 23, 2016 at 3:14

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