Light Exposure During Fermentation

I thought the common perspective was to ferment in a dark place, but in many homebrew fermentation pictures, I see carboys in the corner of ordinary rooms (i.e. not dark closets).

I'd like to have my fermenter in plain view so I can watch it, it seems others do too.

What is an acceptable amount of light exposure during fermentation?

You need to keep it as dark as possible all the time. The best way to do this is to cover it with a black or dark T-shirt. You can lift the shirt to see the progress and then replace it. You don't have to worry about having it in a totally dark place.

i keep my fermenters in our closet in our bedroom, it has no windows and the only natural light that gets in there has to travel threw the bedroom windows and our blinds are always closed, threw the bathroom then into the closet but i keep the fermenters in off to the side so no light gets to the fermenters. i also use a button up long sleeve camo shirt to wrap around the carboy to keep the florecent light out.

maybe im just parinoid lol not sure if it has much affect on beer in the primary or secondary but i do know it has an affect on beer in the bottle espically clear glass

I think its more about avoiding excessive sunlight. sunlight has UVA/UVB rays that'll harm yeast. Not to mention the heat generated by sunlight hitting a stout in a glass carboy

the t-shirt over the carboy method works well. I did a mead once like that with no ill effects or off flavors.

You must keep all light sources, not just sunlight, to a minimum any time after there are hops involved. It is the photons in certain wave lengths of light that will have a photochemical reaction with the hop compounds and cause skunking.

FWIW, skunking is a very accurate description of what is happening to beer exposed to light because the chemical compounds that are produced are almost chemically identical to what a skunk produces from its scent glands.

Jester369 said:

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I'm thinking the T-shirt looks much better on your SWMBO. The carboy just isn't all that shapely.

I got regular lights on in the room from time to time and never got skunk beer at all. I make sure there is no sunlight on it.

I was told sunlight makes it skunky not regular lights.

Raffie said:

I got regular lights on in the room from time to time and never got skunk beer at all. I make sure there is no sunlight on it.

I was told sunlight makes it skunky not regular lights.

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Beer in green glass, imported from Europe has the reputation of being skunky. That is due to them sitting on the shelf in stores with flourecent or incandecant lights, not sitting out in the sun.

Green glass lets the wave lengths of light, from any light source, pass through and react with the hop compounds, brown glass does not. It's not an opinion, it's science.

johnsma22 said:

Beer in green glass, imported from Europe has the reputation of being skunky. That is due to them sitting on the shelf in stores with flourecent or incandecant lights, not sitting out in the sun.

Green glass lets the wave lengths of light, from any light source, pass through and react with the hop compounds, brown glass does not. It's not an opinion, it's science.

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Cool stuff, starter book I read while ago and few friends said only sunlight.

Good to know thx...

Actually, it's not so much because the bottle is green as much as it is because it is more transparent. In other words, it has more to do with the efficiency of the glass as a "filter" more than the bandpass of the "filter" itself. Brown bottles are just more efficient, allowing less of the other frequency's to pass, and in particular, UV light. However, it's not 100% efficient, meaning that it too will allow enough UV rays to skunk your beer if given enough exposure. So, I wouldn't assume that just because it's brown means that you can safely keep it stored in the light (any light, artificial or natural).

I do all fermentation in glass in the basement. A few overhead lights and ambient sunlight (through block windows)-but overall pretty dark. I keep bottled beers down there too-no skunking so far.

Seems like even if it's exposed to some light, it's not the same as getting shipped over from Holland then sitting on a beer cooler shelf for months under flourescent lights.

I use the boxes my carboys come in to cover them and block out light. I also ferment in my basement, which is fairly dark anyways.

I cover my 5 gal carboys with an inverted paper grocery bag with a hole cut in the bottom for the lock and neck of the carboy. Cheap, stores flat and covers the carboy about perfectly.

i use my brew closet and my fermtation chiller. no light on my brew, thx.

There is some info about this at "zymipedia":

http://www.zymipedia.com/index.php?title=Light_Struck_Beer

To summarize what they are saying, visible and UV light both interact with hops to make the skunky chemicals. Brown and green bottles reduce both visible and UV light, but brown is better simply because brown bottles tend to be more opaque than green bottles, not necessarily because of the color.

I would guess that because indoor light is far less intense than sunlight--regardless of wavelength--the indoor light generally causes less skunkiness. I am still curious as to whether particular frequencies of light cause the problem more, or if it is just the bombardment of photons of any frequency.

well I may not understand all the science behind it, but my carboys are kept in the dark (if not in the chest freezerlager then with towels draped over 'em) and the only clear bottles I put beer in are the ones going to people I don't expect to get 'em back from.

I dont understand how people brew during the day then. If I brew outside sunlight is goin to hit the beer while it is boiling and while it is cooling and being transferred. Shouldn't all those beers be skunky?

beerrunner75 said:

I am still curious as to whether particular frequencies of light cause the problem more, or if it is just the bombardment of photons of any frequency.

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From a point of photo-chemistry, the general rule of thumb is the shorter the wavelength (i.e. higher the frequency, i.e. higher the energy of the photon, i.e. stuff towards the blue/violet end of the spectrum) will have a greater potential to photo-oxidize materials than less-energetic (i.e. yellow-red end of spectrum) photons.

As always, rules of thumb have exceptions - most chemicals will have wavelengths of light they preferentially absorb. If exposed to those wavelengths the chemical has a greater potential to be photo-oxidized than the wavelength alone would suggest.

In terms of brewing, dark is best, and if they have to be in the light non-fluorescents are better (fluro's produce UV). But practically speaking, you should be fine so long as you're not leaving the carboy out in the sun, and so long as you're not keeping it in a room with fluorescent bulbs on 24/7.

Bryan

EDIT: Found an absorbance spectra for riboflavin, which according the article linked to by beerrunner is the major source of photo-oxidation. The main absorbance peaks are in the UV (wavelengths below 400nm), along with minor peaks at ~350nm (violet/near UV) and ~450nm (blue). Very little absorbance past 500nm, meaning green, yellow, orange and red light should be relatively harmless.

I'd be interested in some sort of data that plots "skunkyness", for a lack of a better term, against time exposed to light. There has to be a correlation between the two, one would just need to find a way to quantify "skunky"

Niemer said:

I'd be interested in some sort of data that plots "skunkyness", for a lack of a better term, against time exposed to light. There has to be a correlation between the two, one would just need to find a way to quantify "skunky"

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I'm sure there would be a correlation, but I think such a table would be useless. The rate of "skunkification" (sounds like a punk band) would be dependent on a whole host of things - amount of light, its spectral makeup (i.e. how much of the light is in the "bad" wavelengths), the amount of photo-sensitizers (riboflavin) in the brew, the amount of hop oils in the brew, probably even the makeup of the hop oil (I'd suspect that some are more sensitive, so different kinds of hops would be more sensitive). Even the amounts of O2 in the brew would impact on the rate of skunification.

Bryan

Bryan

You'd just have to control those variables. Run all beers through the same tests with the same parameters. A day in august should work. Just get an asst of colored bottles. bottle the same stuff. leave them out all day. drink @ night. Some for 2hrs, some 4hrs, whatever. Compare to the control sample. What 9, maybe 12-12 oz beers. use one you messed up a little. the control is still the control. You'll get it, good luck making a chart. Like to see it if u do.

I actually have a Belgian ale that was brewed in complete darkness on the primary. We used nightvision goggles and brewed in the dead of night. It will never see sunlight until the day its consumed.

I wonder, do you think the folks at Corona or Heiniken purposely expose their beers to heavy UV to attain the taste they have?
My wifes' 3rd son asked if I could come up with a recipe of one or the other. Thats not going to happen (firstly, I don't brew beers I don't like -and secondly... No, just no.)

I just took a couple of my son's old 5-6T shirts. They fit a 5th gallon carboy perfectly

I usually ferment in a frig but if I don't I wrap a towel around a carboy. It's much more opaque than a tshirt and you can buy them for $4 or $5 at Target.

If anyone needs proof of the effects of light on beer they should start bottling and carbing in uncovered clear glass bottles in addition to fermenting in a carboy under direct room light. Let me know how it goes.

Did anyone actually do any of this research? I have a black IPA that's been near a window. There is a blanket that covers the window, it does not let light through, but there is sunlight coming through the bottom where the blanket does not touch the wall. I wonder if this enough to skunk my ale?

You should use red lights, like the Navy uses for berthing spaces after taps. As a plus they don't ruin your night vision.

I did a test on this, I brewed up 5g split it into 2 clear carboys, put one in the dark in my closet covered by a shirt, I put the other in my living room on the far side where no sunlight would hit it but light from my room did.

I keg, (too much work to bottle n e more) so it obviously went in to 2 kegs simultaneously and was drank 3 days later. During kegging I sampled and both out of the tap cold and carbed and the sample pulled during kegging tasted identical to each other.

I also have tried the same thing with leaving one next to an open window with plenty! of sunlight. And the other in the dark. Needless to say the one in sunlight was not drinkable, skunky and disgusting!

I have learned that it is the UVA/UVB sunlight that skunks your beer not your little 60w light bulbs in ur house.

I don't rightly know the science behind this but my experiment speaks dividends IMHO.

Forgive me for coming late to this discussion, and some of my questions on light and fermentation have been answered by reading the rest of this thread. While there seems to be a few different thoughts on the matter what skunks beer, does this look like a fairly safe arrangement for me to ferment in my kitchen?
The ale pail is on the right covered with a pink/orange towel. I am brewing a saison, so heat is not so much of an issue, but the towel does seem to be holding in some of the fermentation warmth. Can I leave the towel off, or will the light from the window blinds become an issue? I have never had an issue before with skunking (I don't think), but would love some advice from a more experienced brewer. Any thoughts would be greatly appreciated. (Yes, my kitchen is a bit of a mess).