Effect of UV on krausen?

[agusus]

This is not a big deal, but just wondering if anyone knows if light/UV can affect the color of beer, particularly the krausen. I noticed this weird pattern on my stout which is at hour 36 of fermentation.

Half of the krausen has big brown bubbles, like the surface of the moon, and the other half has very small bubbles - mostly white with some brown ones mixed in.
I always keep my carboy in a water bath with a white plastic garbage bag covering the top. I realized though that the white garbage bags still let some light through; I just haven't gotten a chance to get black garbage bags yet. The half of the krausen that is darker with larger bubbles is on the side of the carboy that would be facing the sunlight in my apartment. The whiter side is towards the wall and would have been shielded more from sun rays. I can't think of any other reasons there would be this distinct line with such a big difference in appearance. Since I use a water bath, temperature should be quite uniform (also note this krausen developed before I put in the ice cubes). Also, the carboy is mostly level with the ground, and the wort was thoroughly mixed.

 

[BargainFittings]

The coloring is caused by color components in the beer. Particles and yeast will pick up the color and carry it into the krausen. Its basically yeast and protein foam.

 

[Cpt_Kirks]

Krausen tends to contain a lot of hop material. UV reacts with some hop components producing "Skunky" smells and tastes.

Keep the UV off the ferementer if possible.

 

[BargainFittings]

The half of the krausen that is darker with larger bubbles is on the side of the carboy that would be facing the sunlight in my apartment. The whiter side is towards the wall and would have been shielded more from sun rays.

I thought on it some more and its probably just a difference in temperature. The warmer side is probably causing the beer to swirl up toward that side.

 

[dontman]

awesome pics.

But listen to Cpt Kirk. UV + Hops = SKUNK There is no cure for skunked beer and it is nasty as all heck.

If you are getting enough direct sunlight on your carboy to actually affect the temp then you are getting way too much uv on your beer.

 

[BargainFittings]

I don't think a white garbage bag inside a room is going to transfer much if any UV light.

I would think that the blue tub will warm up if you get some sunlight on it.

 

[agusus]

I think BargainFittings has it right – the blue tub probably heated up a bit during the day and got a slight temperature gradient in the water.

The white garbage bags are pretty opaque – I think they would break up any UV light before hitting the carboy, so I’m not too worried about skunking (plus I’ve used these bags for 5-6 other beers already). The thought I had last week was that they probably still allow a little light through - they don’t create pitch blackness - so in theory a minuscule amount of UV could be reaching the beer. But my question was more just one of scientific curiosity – I was wondering how the heck my krausen had a distinct line down the middle – it was like the yeasties were somehow sensing the magnetic poles or a polarity or just liked one side more than the other.
Temperature gradient sounds plausible; or maybe when I put the carboy into the tub I tilted it and some of the sediment/trub amassed in larger amounts on the bottom of one side.

 

[BrewOnBoard]

Looking at the photos (and knowing very little about beer) I would suggest it has to do with all of your ice being on one side of the fermenter. Temp is directly proportional to yeast activity yes? So perhaps this translates to bubble size and character.

BoB

 

[Cpt_Kirks]

Oddly enough, there are people who LIKE the skunk.

They go so far as to set clear bottles out on the porch to get their skunk "goodness".

 

[dontman]

Oddly enough, there are people who LIKE the skunk.

They go so far as to set clear bottles out on the porch to get their skunk "goodness".

Yeah, they're called Corona drinkers.

 

[naterzr2]

Just curious how your stout turned out? I have a sweet stout doing the same thing. I contribute it to temperature differences on the carboy. I had a fan blowing near it and that was the side I got the darker krausen...

 

[agusus]

Yup, it came out fine. I guess the weird difference was due to a temperature gradient most likely.