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Old 01-13-2007, 10:46 PM   #1
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Default How bad is light during fermentation?

Ok, here I go again with my questions... so how critical is it to keep your brew in the dark? How dark is adequate? If I leave my carboy in the kitchen counter (no direct sunlight) for a whole day after pitching, will I have off flavors? Thanks.

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Old 01-13-2007, 10:54 PM   #2
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I can't say for sure if that limited exposure will cause any problems. I doubt that it would. If you're worried about it, get a dark, opaque bag and put it over the carboy with the airlock sticking through. Or, find a box that will fit over and do the same.

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Old 01-13-2007, 11:09 PM   #3
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It's probably not an issue, but why not just put it in its final fermenting place out of light?

The lightstruck issues that beers can suffer from only happen in fermented (or fermenting) wort, so the odds of yours getting lightstruck in indirect light right after pitching seem slim, but I generally don't take unnecessary risks unless I have to.

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Old 01-13-2007, 11:20 PM   #4
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Quote:
Originally Posted by Baron von BeeGee
but I generally don't take unnecessary risks unless I have to.

Then they're not unnecessary are they? :P



I always throw an old t-shirt over my carboys just to be safe.
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Old 01-14-2007, 12:02 AM   #5
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Skunking takes direct UV, but why risk it? Never know how much reflected light it would get. Wrap it in a towel & that will also keep the temperature stable.

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Old 01-14-2007, 01:13 AM   #6
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Skunking is a photochemical reaction. It only needs the presence of photons in visible light to cause the reaction. Blue light, and to a lesser extent green and a bit of near ultraviolet are the most damaging to beer.

Most wavelengths of ultraviolet light are not a concern because glass blocks them quite effectively (that’s why you don’t get sunburned in your car).

The brighter the light and the longer bottles sit in that light the stronger the skunky smell will be. Even dark brown bottles won't guard a beer from the bright fluorescent lights for very long.

The hop compounds that are responsible for making beer bitter are called isomerized alpha-acids. These chemicals, along with sulfur compounds found in beer, are also culpable in beer skunking. When light hits beer, it provides the energy necessary to drive a reaction that transforms the iso-alpha-acids into 3-methyl-2-butene-1-thiol. The “thiol” part of that name indicates that there is sulfur present. Sulfur compounds often have strong, offensive aromas. Skunks, have evolved the ability to produce this chemical, and use it for self-defense.

In a sense, the aroma of light-struck beer doesn’t just resemble skunk spray, it is skunk spray!

John

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Old 01-14-2007, 02:10 AM   #7
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Quote:
Originally Posted by Chairman Cheyco
Then they're not unnecessary are they? :P
Sounds more daring and 007-ish my way.
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Old 01-14-2007, 05:07 PM   #8
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You don't ferment beer in the light more so for biological reasons, not chemical ones!!!

If any one has taken microbiology and learned of all the different ways to kill bacteria (and particularly yeasts!) one of the best ways is exposure to UV light.

The UV pretty much kills the yeast causing them burst or break open. And as you know when yeast dies you get off flavors!

We did a test (but with bacteria) We exposed a plate of Staphlo Cacus arueus (which is less reative to UV than beer yeast) to 60 seconds of direct UV light. They all died. All of them. Don't put yeast in any sort of light, they will die and the ones that survive are only survivng in the shadow of the dead bodies laying ontop of them.

On a chemical level there might only be 1 or 2 photo reactive compounds that affect the bear on a marginal level compared to the yeast.

When making anything with yeast, keep in a pitch black place.

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Old 01-14-2007, 08:29 PM   #9
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I've got tons of black T-shirts and I just slip one over the fermenter and worry is gone. If it makes much difference I don't know but it only takes a second so why not?

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Old 01-15-2007, 02:07 AM   #10
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Quote:
Originally Posted by RichBrewer
I've got tons of black T-shirts and I just slip one over the fermenter and worry is gone. If it makes much difference I don't know but it only takes a second so why not?
But I don't have a single black T-shirt.

For the past 12 years, I've done my fermenting in a corner of the kitchen that is shielded from direct sunlight and fluorescent light. I dont "dress" my carboys, and I've never had a problem.

-a.
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