Does outside brewing skunk your beer?

I brew in a brew shed, so this doesn't really affect me, but I see a lot of photos of people brewing out on a deck or in their driveway on HBT. How do you keep from skunking your beer if you're brewing out in the blazing sun?

If someone posts a picture on HBT of a carboy anywhere near a window or flourescent light there will be a half dozen people yelling to cover it up. But I see tons of pictures of people brewing outside, boiling and cooling wort, and draining into glass carboys in the blazing sun where the UV is a million times stronger than indoors, and nobody says a thing.

As I said, it doesn't affect me, but I just find it curious and was wondering what people thought.

There was a post by Revvy just the other day saying light will only skunk fermented beer, not wort.

So why is it so important to keep hops out of sunlight then, if they will only skunk in fermented beer? I've always heard that hops will skunk if exposed to sun, so it seems like they would skunk in unfermented wort as well. Everything I've read about drying my garden hops say to dry them somewhere away from daylight.

My hops will not grow without sunlight.

The wort is only exposed to sun for at most a couple hours while brewing. That's not enough to skunk beer, even in a carboy.

Found some info on hops and sunlight on the wiki. Looks like dried hops can discolor in the sun, but not skunk. It's the isomerized alpha acids exposed to UV that are thought to cause skunking of beer.

https://www.homebrewtalk.com/wiki/index.php/Can_light_skunk_hops%3F

But that would bring me back to the original question of why wouldn't your beer skunk while brewing outside. The boiling and cooled wort is full of isomerized alpha acids.

How much direct sunlight gets into your brew pot?

cfonnes said:

How much direct sunlight gets into your brew pot?

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I'm speaking hypothetically, since I brew indoors in a brew shed, but if it was summertime mid-day, the sun could be coming down straight into your kettle and carboy.

A lot of people on this site and others have noted that beer can skunk in minutes in direct sun:

https://www.homebrewtalk.com/f39/how-fast-will-beer-skunk-190630/

http://www.homebrewersassociation.org/forum/index.php?topic=4876.0

I've never had a beer skunking problem personally, but I just can't work it out in my head how it's not OK to have a fermenter exposed to sun, but it's fine to brew beer in the sun.

I think that skunking would be a concern only later in fermentation when the UV can penetrate further into the [clearer] beer, but that's just a guess without trying to figure out light penetrations vs. srm/cloudiness, so ymmv

I don't think it's a concern during the boil. Not much light it getting in, and any skunkyness might very well be boiled off.

I also rack into my carboy in the shade or bring it into my basement and then rack into my fermenters.

mattmcl said:

The wort is only exposed to sun for at most a couple hours while brewing. That's not enough to skunk beer, even in a carboy.

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Try pouring a pale ale on a sunny summer day, take a sip and then set it in the sun for 10 minutes. It'll be nice and skunky...

Maybe the yeast eat the 3-methyl-2-butene-1-thiol

If that were the case, then things like the NATIONAL HOMEBREW DAY BIG BREW DAY, would have to happen at night, eh?

NOT.









Hops skunking has to do with the interraction of isomerized alpha acids from hops, and sunlight in fermented beer.

Not unfermented wort.

When we're brewing out doors the only thing we have to worry about skunking is the beer we're drinking, NOT what we're brewing.

bigljd said:

But that would bring me back to the original question of why wouldn't your beer skunk while brewing outside. The boiling and cooled wort is full of isomerized alpha acids.

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Because it's not BEER yet, it's wort......It's not beer UNTIL IT IS FERMENTED.

Revvy said:

Because it's not BEER yet, it's wort......It's not beer UNTIL IT IS FERMENTED.

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I GET THAT IT'S NOT BEER (no need to shout), but I was hoping for a bit more scientific reason that would explain why skunking doesn't happen in wort, but magically happens in beer. Obviously, if everyones IPA skunked every time they brewed one outside at big brew or whatever, nobody would brew outside. I would just like to understand why the alpha acids are happy in the sun in wort, but not happy in sun once the fermentation starts.

Riboflavin needs to be present for skunking to occur. Fermenting yeast produce riboflavin.

It's only skunked if you have an unlucky encounter with a certain furry animal

Jhenjum said:

Riboflavin needs to be present for skunking to occur. Fermenting yeast produce riboflavin.

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THIS!!! This is the scientific reason you are looking for. Beer would skunk during brewing if riboflavin were present.

Jhenjum said:

Riboflavin needs to be present for skunking to occur. Fermenting yeast produce riboflavin.

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I did not know that! Thanks for solving the riddle for me. Now I can go back to doing more mundane things like killing brain cells with homebrew, and can stop bothering you folks with silly questions.

I don't think the answer is as simple as riboflavin or not. From what I've read UV light can cause the photoxidation of iso-alph-acids without riboflavin, it's visible light that needs the riboflavin to cause the same reaction. Here's a screen capture from a page in the Brewing Science and Practice Textbook

Buna_Bere said:

I don't think the answer is as simple as riboflavin or not. From what I've read UV light can cause the photoxidation of iso-alph-acids without riboflavin, it's visible light that needs the riboflavin to cause the same reaction. Here's a screen capture from a page in the Brewing Science and Practice Textbook

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You are right...it is not as simple as that. We will probably never have a definitive understanding of skunking...think about it, we should be able to google this and learn that beer skunks in 5 minutes, 3 seconds in direct sunlight or something like that. There are a number of interactions happening that affect this situation. Most importantly, individuals respond differnently to the "skunk molecule" are radically different.

Riboflavin is a simplified explaination of the head-scratching question of why outdoor brewing does not skunk like fermented beer does...