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With all the talk about how important it is to sanitize your equipment when brewing, is it acceptable to use a UV sanitizer light on a finished product just to make sure there is no harmful bacteria left in the bottle/brew?

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    Good question, but how would you do that without exposing the product too long to air? – Philippe Nov 19 '15 at 21:06
  • I would assume that, as long as the bottle allows UV light to pass through, it wouldn't need to be exposed to air at all. – Programmer Nov 19 '15 at 21:10
  • @Hooplehead24 Glass for bottles is designed to stop as much UV as possible. Not to mention that in tests "all glasses totally stop UVB" – Mołot Nov 19 '15 at 23:06
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I don't think it's a good idea, but might depend on product. You know why brown bottles are more popular than green or clear? Because light creates bad flavor and aroma in most beers. In my country it's known as skunks aroma. Strong UV lamp will do the same, only much faster. As far as I know, wine doesn't like light either. But I believe there might be some brew that would survive without harm. I just can't recall any.

Sun gives about 0.01 to 1 watt of UV energy per square meter*. UV lamps give between 8 and 20 watt / square meter. Some possibly even more. It only takes two hours to distinctly skunk your beer under direct sunlight. So skunking due to lamp use will happen even faster. This relation is not linear, so it would be up to you to test how much bad flavors lamp would introduce, but I feel convinced amounts will be significant.

There is also another problem. You would either need to pump your beet thorough special installation, risking contamination at later bottling and thus preventing any benefit, or you would try to pump UVB and UVC thorough bottle glass. Glass tends to be opaque to UVB, and probably to UVC*, and it's UVB and UVC that's used for sterilization. So what you would probably sterilize that way is outside of your bottles only. And that's even when we didn't count bottle manufacturers' effort to mitigate skunking. By the way, skunking is also caused by UVA, that's why even brown bottles does not prevent it completely. Sadly, UVA hardly has anything to do with mass killing of bacteria. Even more sadly, most UV lamps gives you some from all three kinds, so ineffective sterilization may still be effective skunk.


* I'll be grateful for hard reference on these points.

  • We call it skunked here too, but it can also refer to beer or wine that's been allowed to warm and cool too many times. A beer can be stored at room temperature, but once you cool it you should try to keep it cooled until you drink it. – Escoce Nov 19 '15 at 19:37
  • @Escoce there may be many ways to this problem. Putting bottle next to a window at sunny day is one I know for sure to work. – Mołot Nov 19 '15 at 19:38
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    yes of course, that's what his answer says, I was just confirming we called it skunked as well, and that it also happens from temp cycling – Escoce Nov 19 '15 at 19:39
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    @Hooplehead24 Two hours in the full summer sun is more than enough. More UV => less time needed. And rections usually need that energy to start, then they can finish without further pumping with photons. For water it's different because there is nothing to react in it. – Mołot Nov 19 '15 at 21:17
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Nope UV is bad for beer. It will make it taste horrible (skunky is one of the aromas that will be produced). I you mean harmful to people, then don't worry. There are no harmful bacteria in beer, they can't survive in the beer and bottle environment. If you mean harmful to the beer, then filtering and pasteurization can remove or kill these organizims. Many beers, usually ones high in alcohol, however, are aged on lees or are otherwise bottle-conditioned and are not pasteurized or filtered.

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    While UV is bad for beer, and will generate off-flavours, bacteria most certainly can survive in finished beer, a cursory search will provide many examples. This is a prime reason for pasteurization and or sterile filtration with commercial breweries. – John Nov 27 '15 at 22:04
  • Not harmful bacteria. They pasteurize and filter mainly for consistency. And there are numerous examples of beers that are not pasteurized or filtered. I've harvested and cultured many yeasts from bottled beers - mainly imports. Friends who own a microbrewery filter for looks as they can't wait for settling. Look here in this forum's post homebrew.stackexchange.com/questions/6230/… – Eric Deloak Nov 28 '15 at 17:10
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    These organisms can be harmful to beer, not people. Lacto and pediococcus have been present in many comm. beers we've plated. The latter can create diacetyl. Pasteurization kills all organisms that can alter the beer (both yeast and bact.) This as you said is for consistency but also shelf life. These will (generally) last much longer than untreated beers. Non-sterile filtering (>0.45um) is for aesthetics. This isn't to say that all beer that aren't pasteurized or st.-filt'ed are contaminated, but rather there's a greater probability they are and will have reduced shelf life as a result – John Nov 28 '15 at 17:22
  • If there are no harmful bacteria in beer, then why do we sterilize the equipment/bottles at all? – Programmer Dec 2 '15 at 14:06
  • You don't sterilize bottles or equipment, you sanitize them. Regardless, you don't do this to kill pathogens. It's to keep organisms you didn't intend to get in beer, to get in. But if you think you are keeping everything out, you don't know about bacteria. It's everywhere, in the air, on your clothes, in dust, everywhere. It gets in the beer. We are OK after we drink it. Spoilage of beer is much easier at the early stages, and that's where you need the best sanitation. I don't think I ever had a spoiled beer after bottling (after hundreds made). – Eric Deloak Dec 2 '15 at 16:44

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