skunk risk

Post #1 made 9 years ago

I boil my wort outside on a propane burner, but bring the kettle inside to chill. Is there a risk of skunking the wort by virtue of the UV light exposure during the 90 minute boil?


Post #2 made 9 years ago
Seems like a good question to me BDP. Whenever "skunking" is discussed it is with regard to packaged beer, not production of it. I guess this is because the "big boys" are unable to move their kettles outdoors!

This excerpt from "Bamforth, a quality perspective" mentions;

"Perhaps the most infamous in-pack flavor change is that induced by the exposure of beer to light. Native iso- α -acids are prone to photochemical degradation by both visible and ultra-violet light which results in the formation of 3-methyl-2-butene-1-thiol. This component, with flavor thresholds reported from 1 to 35 ng/l is reported to have a skunky aroma (the compound is similar to, but not the same as, the major impact compound emitted by skunks). The critical factor though is its low flavor threshold, so that even brief exposures to light can render a beer unpleasant or undrinkable."

My view is that if it can affect beer, it can affect wort too. To what extent though I don't know. I guess your kettle isn't made of clear glass so light can only enter from the top. Mybe that isn't enough light or for enough time, but I do like your thinking though.
Last edited by mally on 25 Mar 2015, 16:07, edited 1 time in total.
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Post #3 made 9 years ago
Thanks Mally. This idea just popped into my head recently. I'll keep on researching this and post back here if I find more detail.


Post #4 made 9 years ago
I like ideas that pop into people's heads :thumbs:.

I read this thread yesterday BDP and mally's reply and it made me stop and think a few times. My thoughts have been...

1. I have never heard of or tasted a skunked beer that could be put down to a boil.
2. In fact, all skunked beers I have had were in a bottle, never from a keg as far as I can remember.(I'm 99% sure of this.)
3. Wort is fairly cloudy so I don't think sunlight would penetrate very deep especially with a vigorous boil going. I imagine everything would be reflected but I don't know the science of this.
4. I would be worried about fermenting in a glass carboy in a naturally bright room especially if sunlight was able to directly hit the carboy.

So, I reckon there is nothing to worry about here.


On a funny note, one HBS owner told me, years ago, that yeast was a living thing and to ferment in as much natural light as possible :roll:. He had a very big shop back then. Probably still does!
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Post #5 made 9 years ago
For a study of Skunked beers and where it can come from, and see how a topic can change... ... ol.132365/

And if you believe Hops contribute to "Skunk-e-ness" and Humulune Oil is to blame. See for a list of Hops Varieties by Humulune Oil Volume.

Or keep the Finished beer in a cool dark Place.
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Post #6 made 9 years ago
I recall a site that listed the types, strength and duration of light and the respective amount of time for beer to become skunked under those various conditions. Of course, I didn't bookmark it :idiot:

I do believe that this reaction will occur in the wort, but to what extent, that will also depend on factors like the amount (surface area), strength, and duration of the UV light exposure when boiling outside, amongst other things (like the amount of hops and their alpha-acid content). Supposedly there are a lot of things going on during the boil, so it would be interesting to know what is happening to those UV converted iso-alpha-acids. If they are volatile, perhaps they would be boiled off (reducing bitterness?). Also, the subsequent fermentation process also removes bitterness, so perhaps these compounds are also reduced in a similar way.

I haven't had any bad experiences yet, but I believe that it would be safest to brew indoors. Unfortunately not something I have the luxury of doing. I'm lucky I guess that I don't live near the equator :)

... or maybe I should just brew at night ;)


Post #7 made 9 years ago
BDP, Humulene, Melts above 168F/75C, Boils off at 194F/90C.

As the wort boils Humulene goes to Iso-Humulene, and if the wort is boiled for more than a few minutes, the Iso-Humulene is pretty much Gone.

The hops that do this, are used as Flavor or Aroma Hop Additions, So skunky-ness can only happen toward the End of boil and After.

If you brew out of Direct Sunlight, there is Very Little Chance the wort can go Skunky.

And if you Bottle in Brown Bottles, there is no way for the beer to go Skunky.

Of Course, if your in the Direct Sunlight, and have clear glass holding the beer....

Watch Steve and James at Basic Brewing talk about Skunking Beer on September 14, 2007 at ... nking-beer
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