Glass Carboy: Does it need to be covered?

So I just picked up a 5 gallon glass carboy for my dry-hopped/fruited beers. Everything I know about glass and UV light tells me a carboy will stop most or all of the minimal UV light coming from household sources. However, I know a lot of folks cover their carboys.

This would be as simple as putting the carboy in the box it came in, but the one thing that has me thinking is temperature. When I do a fruit brew, there will inevitably be a true secondary fermentation. How vigorous that fermentation will be is yet to be seen, but it may be enough to raise temperatures just enough to cause an issue. Probably not, but maybe.

I like to have a fan running full tilt against the side of my primary when it's in full ferment to keep temps in range, and would like to do the same with the secondary when I do fruit brews. But keeping it in the box (or putting some other opaque substance between it and light) would not only prevent that from being possible, but would also insulate the carboy and actually trap heat.

So, now that I've significantly protracted a simple question, what do you guys do? Keep 'em covered or keep 'em exposed?

If the carboy is in a dark closet or at least out of sun light than there is no need to cover. Most people will cover even with indirect sunlight. (Myself included)

I don't think the fermentation from adding fruit will be strong enough to raise your secondary temps that much.

If you still want to keep sunlight out and provide cooling, just wet a black teeshirt and put it on you carboy. You will have to re-wet it once a day but it will do a good job at keeping it cool and dark.

I suppose I'm wondering what the rational is in covering. My brew setup is in the basement, where there is zero sunlight, but artificial light from fluorescent. I've studied UV lighting for reptiles, and I know for a fact that almost no UV light gets through regular household windows (this is why all your furniture and everything else isn't faded horribly). I would also assume that the relatively thick glass of a carboy would filter out almost all remaining UV light, and certainly any little bit of UV light from household lights.

So I suppose I'm asking, does visible light do any damage to beer? I'm not aware of it damaging any food products, as indeed a fair amount of beverages, etc, are bottled in clear glass. But I dunno....

...I'll probably put the carboy in the closet and run the fan, just for my own piece of mind, but I'm still curious regarding this topic.

just put a shirt over the carboy. Yes uv light breaks down some flavors and specifically the hops acids.

scinerd3000 said:

just put a shirt over the carboy. Yes uv light breaks down some flavors and specifically the hops acids.

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But absolutely zero UV light would make it through the walls of the carboy...

...not trying to start one of those goofy forum debates, but I'm genuinely curious to get to the bottom of this one.

Skunking is caused by light with wavelength 520 nm or lower.
This includes visible light up to green.

Commercial beers in clear and green bottles can be skunked
in the cooler or warehouse under fluorescent light.

I cover my carboys with black t-shirts.

It's cheap insurance and good practice to cover them with tshirts anyways. Besides, if you do get a vigorous 2ndary ferment and the carboy blows it's top it'll be easier to clean up the sides of it.

I just place a large black garbage bag down where I'm putting my carboy and when I set the carboy down, I just have to pull the bag up over it.

I cover mine with a black tshirt. I keep mine in a closet and to check how much light was getting in I got in the closet and closed the door. I could see from the little bit of light coming through the bottom so I put some foam on the bottom and now inside is pitch black. I still cover it though...I'm pretty sure that light damage is not cumulative so short bursts of even direct sunlight won't hurt. I've been to several lhbs that had primaries and secondaries in their shop uncovered in bright, yet indirect sunlight all day everyday.

blue/green light is the most damaging to beer. that definitely gets through windows and carboys.

swmbo made me a "carboy koozie" thingie. it's just some fabric that she sewed all together that's tapered, and fits over the airlock and completely covers every inch of glass. overkill, but cute nonetheless.

chainsawbrewing said:

swmbo made me a "carboy koozie" thingie. it's just some fabric that she sewed all together that's tapered, and fits over the airlock and completely covers every inch of glass. overkill, but cute nonetheless.

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Picture?

2345

egolla said:

Skunking is caused by light with wavelength 520 nm or lower.

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That answers it. Thank you, sir. I might have to get a bit creative with the cooling solution, but I'll figure it out.

egolla said:

Skunking is caused by light with wavelength 520 nm or lower.

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Normal glass will block most of the UV light below 300 nm, but most everything above 350 nm will get through. So for safe measure you might want to cover it up.

White float glass Transmission Curve