Skunking & Sunlight

[KillerRx4]

Ive just relocated my brewery & where I used to have a big shed to brew in, I now find myself brewing outdoors.

This morning while i was waiting for my whirlpool to settle, glancing at the empty cube in direct sunlight ready to be filled with hot wort I pondered.... What are the skunking effects likely to be on unfermented wort?

From my limited understanding it is the reaction of isomerised alpha acids when exposed to UV & happens very quickly? Am I causing issues exposing the wort to sunlight at this stage of the process?

I ended up covering the cube with a sheet/rag as a precaution but id love to know the deal.

Anyone?

 

[Thirsty Boy]

Yes you are

I have no idea how much or if it would be a problem. But for sure, if the UV is getting through the cube, then its skunking the beer. I never let my filled cubes sit in direct sunlight for this very reason.

It might not be a problem, but if I keep them out of the sun, I know its not a problem.

TB

 

[technocat]

I brew inside but my fermenters are up on a bench by a window. As I consider UV having a negative impact on beer I keep them covered with an insulated blanket which stabilizes temperature and keeps sunlight out. Skunking has never been an issue so I guess keeping the light off your brew is the way to go.


Cheers :icon_cheers:

 

[newguy]

Skunking occurs due to short wavelength light interacting with hop compounds. From what I've read, blue-green light is the longest wavelength that's dangerous, but shorter wavelengths (ultraviolet, x-ray, gamma ray) are just as dangerous. From experience it takes about 3-5 minutes in full sun for a full pint glass of relatively clear beer (colour didn't seem to matter) to skunk. A fermenter would probably take longer to fully skunk, but partial skunking would definitely start as soon as the fermenter was exposed to sunlight.

I brew outside, but I always ensure that my uncovered kettle will always be in shadow once the hops hit the wort. In my experience only direct sunlight is sufficient to skunk a brew. I've heard people talk about fluorescent lights doing the deed but if you crunch the numbers, it would take a reaaaaaally long time for a 40W bulb to accomplish the same thing as the sun.

 

[Stuster]

AFAIK you should be ok. The skunking compounds interact with light, as newguy said especially with blue-end waves. However, the chemicals that make this are produced by the yeast during fermentation. So the beer in the kettle and in cubes should be fine, but by the time it's fermenting then keep it out of the light.


From here.

Brewing chemists attribute skunky flavor to 3-methylbut-2-ene-1-thiol, a constituent of skunk spray. This compound arises from a reaction that light triggers within the beer, and the resulting taste can overwhelm other flavors.

"Humans are very sensitive to this compound," says Denis De Keukeleire of Ghent University in Belgium. 3-methylbut-2-ene-1-thiol is detectable in quantities as small as 0.004 micrograms ([micro]g) per liter. This amount can form in minutes when beer is exposed to bright sunlight, he says.

Riboflavin, a compound produced by yeast during fermentation, absorbs energy from light at wavelengths of 350 to 500 nanometers (nm). It transfers the energy to iso-alpha acids, the compounds that give beer bitterness. They then release free radicals--small, unstable chemical fragments--that react with sulfur compounds produced by the yeast. The result is the offending thiol.

 

[Thirsty Boy]

AFAIK you should be ok. The skunking compounds interact with light, as newguy said especially with blue-end waves. However, the chemicals that make this are produced by the yeast during fermentation. So the beer in the kettle and in cubes should be fine, but by the time it's fermenting then keep it out of the light.


From here.

Partially true - but there is riboflavin in both barley and malt. Skunking can still happen in fermented wort. It certainly cant if you lob a blanket over the cube.

 

[Stuster]

Partially true - but there is riboflavin in both barley and malt. Skunking can still happen in fermented wort. It certainly cant if you lob a blanket over the cube.

Unfermented wort?

Anyway, interesting. Just had heard that it was more of an issue with fermented wort. I do try to keep it covered at all points. As you say, better to be safe. There are certainly lots of commercial fresh wort cubes sitting in the sun in HBSs.

 

[Thirsty Boy]

fat fingers -you are correct, I meant un-fermented

and you were of course further correct that if the riboflavin is the thing that enables the transfer of energy to that bond, then its going to be less of an issue in pre-fermentation wort

Sitting in the sun is one of the reasons I would be pretty careful about choosing those cubes - still, good point. Perhaps it is so significantly less of an issue, as to not be one at all?? Have to look into it further, but on the face of it I reckon you are probably right and I am probably wrong.

 

[james hughes]

Hi all,
I'm fairly new to all this. I'm on my 6th brew.
Do we know how much light is too much?
I am using a white plastic 30 litre fermenting bin.
It's sitting in a room with indirect sunlight and a normal 60 watt light bulb.
I'm using a heat belt which seems to keep the temperature nice and stable at 24 degrees, but when I throw a cover over it to protect from light, it raises the temperature too much.
Any idea if this amount of light is ok, or should I change the environment?

cheers
James

 

[Georgedgerton]

Hi all,
I'm fairly new to all this. I'm on my 6th brew.
Do we know how much light is too much?
I am using a white plastic 30 litre fermenting bin.
It's sitting in a room with indirect sunlight and a normal 60 watt light bulb.
I'm using a heat belt which seems to keep the temperature nice and stable at 24 degrees, but when I throw a cover over it to protect from light, it raises the temperature too much.
Any idea if this amount of light is ok, or should I change the environment?

cheers
James

Easy fix (even if it is only to put your mind at ease) Large black plastic garden bag (type with the draw string top) cut the bottom off so what's left is the same length as the fermenter, drop bag over fermenter and pull the string leaving a bit of an air gap at the top - hey walla

 

[stm]

I'm using a heat belt which seems to keep the temperature nice and stable at 24 degrees, but when I throw a cover over it to protect from light, it raises the temperature too much.

cheers
James

And please note that 24 degrees is a little on the high side of ideal (for an ale yeast). Try no heat belt, throw your cover over, and see what the temp ends up at. If it settles anywhere between 17 and 20, that's pretty good.

 

[Scruffy]

Sound like you need a wet towel rather than a bin liner... keep the temp







DOWN...

 

[Power Wolf]

Hey james,
The other option is cover your brew and invest in a timer if you haven't got one. A little playing around and you might work out that your heat mat works perfectly when you cover your brew just by setting the timer/heat mat to an hour on, an hour off for example...
Cheers!

 

[Thirsty Boy]

you'll be OK. Incandescent bulbs don't give out a hell of a lot of the light that is an issue - indirect sunlight will get it eventually... but only eventually. Keep it out of the direct sunlight and it will be fine.

But skunking can happen fast ... you know that smell that you get in pub beer gardens on a hot sunny day. Skunking - everybody's glass of beer and all teh lovely dregs. Getting lightstruck. Happens in minutes.

Demo - take one stubbie of Pure Blonde - pour half into a pot glass, put coaster on top to keep out the flies and leave it in bright direct sunlight for 3 minutes - pour the other half into a glass and leave it in the shade. Give both beers a swirl and then give em a smell.

Pure blode is a good one for demonstrating light strike, because it has such light body and not a lot of flavour apart from hops, of which it has a decent whack. The skunk comes out really noticably.

TB

 

[katzke]

Interesting subject.

It got me to thinking of how I handle my beer. I cover the fermentor when I put it away to ferment. But other then that I do not have a cover on it when transferring the wort in or the beer out.

Any of you go the extra effort and make sure it is covered at all times?

I did ask a brewing expert why homebrew does not keep the hop flavor as well as micro brewed beer. Never did get an answer and now I wonder if the way we move wort and beer around may be part of the answer.

 

[mwd]

Just wondering about the Fresh Wort Kits just sitting on the shelf in the LHBS. Not actually in direct sunlight but bright daylight and flouro lights.

Anybody bought a skunked RWK ?

 

[Georgedgerton]

Sound like you need a wet towel rather than a bin liner... keep the temp







DOWN...

Just to clarify, my remark regards the bin liner had to do with keeping the light out and nothing to do with temperature control

 

[BjornJ]

Demo - take one stubbie of Pure Blonde - pour half into a pot glass, put coaster on top to keep out the flies and leave it in bright direct sunlight for 3 minutes - pour the other half into a glass and leave it in the shade. Give both beers a swirl and then give em a smell.

Pure blode is a good one for demonstrating light strike, because it has such light body and not a lot of flavour apart from hops, of which it has a decent whack. The skunk comes out really noticably.

TB

I will have to try this for myself to believe it, does it actually "skunk" that quickly?
I have read about how light affect the beer and it seems to make sense to store it in brown bottles to reduce the light getting through. But it sounds like a stretch to say having a glass of beer outside in summer time destroys the beer? Wouldn't we all be drinking beer in the shade if that was the case?
(not saying it's not true of course, just saying it sounds funny)
I will definetly try this to see if I can smell and or taste it.
(today it's raining, but there may still be hope for the weekend)

 

[buttersd70]

I will have to try this for myself to believe it, does it actually "skunk" that quickly?

Oh yeah. Doesn't take long at all. Surprised that no bright spark at a glass company has come up with UV resistant beer glasses. :lol: