Is 'light struck' a real thing?

[DiscDuffer]

I keep seeing all of these pictures on here with uncovered fermentors. Carboys in sunlight rooms and glass fronted refrigerators. Do people not care or notice the difference? Have I been wasting my time and energy in making sure mine are covered?

 

[Yooper]

No- you're right. You want to protect your beer (and wine/cider/mead) from UV light and keep the carboys covered.

 

[DiscDuffer]

And I have just been doing it for beer with hops in it.

 

[MaxStout]

I've poured an IPA into a glass, sat on the deck on a sunny day and tasted skunk in the last few sips. It doesn't take long. It'll skunk in a glass fermenter, too. Pull an old dark-colored t-shirt over it or cover with a black plastic garbage bag.

 

[Qhrumphf]

I've definitely had pints of European lagers skunk outside on a sunny day before finishing the glass.

I've some awfully skunked IPAs come out of a brown bottle, for that matter.

 

[filthyastronaut]

Depends on how much light it's getting. Generally it's a good idea to cover it, regardless.

Also, by beer with hops in it do you mean dry hops? Skunking will only happen to isomerized alpha acids, which you don't get from dry hops, so if you don't cover other beers then the area you ferment probably doesn't get enough light to be an issue.

 

[Dustin_J]

Take a bottle of hoppy beer and set it in a window for a while. Keep another in the fridge to compare - definitely a thing and can be quite pronounced

 

[RPh_Guy]

Skunking will only happen to isomerized alpha acids

Do you have a reference for this?

 

[seatazzz]

I can't stand Corona for that very reason. I've also had some skunked Heineken in my time, darn green bottles. My fermenters live in the ferment fridge, only time I cover them is if I'm using the heat lamp to keep the temperature where I need it. Old black t-shirts work great.

 

[bruce_the_loon]

Do you have a reference for this?

Readable paper covering an experiment. https://scholarblogs.emory.edu/eurj/files/2014/05/UVBeerProject_Final_pdf.pdf

PUBMED link to a paper behind a journal paywall on the process. https://www.ncbi.nlm.nih.gov/pubmed/11757646

Edited to add unpaywalled link to the above paper. https://www.researchgate.net/public...time-resolved_electron_paramagnetic_resonance

Both papers discuss how the iso-alpha-acids are photo-sensitive to UV and how UV causes the conversion of iso-alpha-acids into thiols which cause the offensive odours and flavours.

 

[mongoose33]

Yeah, skunking is a thing. @bruce_the_loon gave good resources to understand why.

The worst source of skunking is sunshine. If you want to test this, take a lighter beer, an IPA is a good choice, and put it in direct sunlight for 30 minutes. Keep it on ice if you want to test it right away. Pour into a glass and enjoy....if you can.

Or, you could use a rinsed-out and sanitized Diet Coke plastic bottle. Fill off a keg, cap, and put in the sun. Or, if you bottle rather than keg, use it as a bottle (it actually works). Keep in the dark for the normal time you let the beer condition, then put in the sun for half an hour, chill, and enjoy .

I attended an off-flavor workshop a couple years back where they took a beer, put in the sunshine for the afternoon, then served it to us. Wow, very skunky.

***********

BTW, skunkiness is actually a feature in a few beers. Corona is famous for this. In fact, the people putting on the off-flavor workshop claimed that the whole "A Corona gets its lime" thing was in response to skunkiness. Their bottles are clear and of course, almost impossible to avoid skunking unless you keep them in the dark forever. Anyway, they knew of the skunkiness and discovered that the lime helped mitigate the sensation of skunkiness. So now the necessity has become its virtue.

***********

Fluourescent light bulbs tend to put off UV light, which is what causes skunkiness. So does the sun, of course. Incandescent bulbs, not so much.

I used to ferment in my basement; I had incandescent bulbs for light, never noticed a skunkiness (and I'm very sensitive to that odor). Still, the best practice is to keep the wort/beer out of the light period. Fluourescent light is not good.

***********

I have a sight glass on the bottom of my stainless conical. Of course, for the most part, the beer isn't exposed to light, but that sight glass is exposed to light. I've never noticed any skunkiness from beer produced in that fermenter, but the sun does shine through the window, and the beer in the sight glass is exposed. Even though I haven't seen a problem, I'll probably cut a piece of thin cardboard to wrap around it.

 

[MaxStout]

CSB:

There used to be a specialty beer store in the Twin Cities that sold hard-to-find craft beers (Four Firkins). You'd walk in and you felt like you were in a cavern--kind of dark. The front windows were covered in tinted film. What lighting they had was all LED, several years ago when LED lamps were not cheap. They went the extra mile to ensure their beers didn't end up light-struck--at least not on their watch. In contrast to most stores that keep everything under fluorescent lighting.

They eventually went out of business when craft beer became more mainstream.

/CSB

 

[Vale71]

***********

BTW, skunkiness is actually a feature in a few beers. Corona is famous for this. In fact, the people putting on the off-flavor workshop claimed that the whole "A Corona gets its lime" thing was in response to skunkiness. Their bottles are clear and of course, almost impossible to avoid skunking unless you keep them in the dark forever. Anyway, they knew of the skunkiness and discovered that the lime helped mitigate the sensation of skunkiness. So now the necessity has become its virtue.

***********

Corona bottles are treated with an anti-UV coating and the beer is hopped using tetra-iso extract which is much more resilient to skunking than regular extract and still the beer comes out lightly skunked. The brewery is very much aware of the issue and has done much more than just suggest a slice of lime as a remedy.

 

[Vale71]

CSB:

There used to be a specialty beer store in the Twin Cities that sold hard-to-find craft beers (Four Firkins). You'd walk in and you felt like you were in a cavern--kind of dark. The front windows were covered in tinted film. What lighting they had was all LED, several years ago when LED lamps were not cheap. They went the extra mile to ensure their beers didn't end up light-struck--at least not on their watch. In contrast to most stores that keep everything under fluorescent lighting.

They eventually went out of business when craft beer became more mainstream.

/CSB

When I lived in Munich my beer supplier of choice was in the basement level of a local shopping mall. Entrance was directly from the underground parking garage and it had absolutely no windows whatsoever. Never brought home a skunky beer from there...

 

[mongoose33]

Corona bottles are treated with an anti-UV coating and the beer is hopped using tetra-iso extract which is much more resilient to skunking than regular extract and still the beer comes out lightly skunked. The brewery is very much aware of the issue and has done much more than just suggest a slice of lime as a remedy.

It doesn't matter what they've done, does it?

It's skunky. That's why the lime. As I said above, they've taken a problem and turned it into a virtue.

There's a really easy solution to this problem: stop using clear bottles. Or do what Miller has done. They've gotten a process down that prevents skunking in clear bottles.

 

[Vale71]

It doesn't matter what they've done, does it?

It's skunky. That's why the lime. As I said above, they've taken a problem and turned it into a virtue.

There's a really easy solution to this problem: stop using clear bottles. Or do what Miller has done. They've gotten a process down that prevents skunking in clear bottles.

Of course it does matter. With regular glass and regular extract the beer would get so skunky that it would make you throw up as soon as you open the bottle, forget about actually drinking it.

The process that Miller employs is just the same tetra-iso extract (or possibly rho extract, which is similar) that Corona uses.

 

[ncbrewer]

Some craft breweries are canning their beer. I like getting bottles for bottling my homebrew, but I think cans are the better way to go.