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Thursday, May 19, 2011

Light Struck Wort?

Here's a question for you homebrewers: if you're brewing outside in the bright, midday sunshine, will it get lightstruck during the boil? This is more academic than anything; I usually find a patch of shade. Still, I've always wondered.


  1. I am under the impression that light-struck and the skunking effect is a result of UV on the yeast, so it shouldn't have anything at all to do with the wort and boil.

  2. It's the hops not the yeast. I have not tested it but I would think sunlight + boil would be something to avoid.

  3. There may be other reactions going on with UV rays in wort but the light-struck character comes from a reaction with alpha acids in hops.

  4. I doubt it would have much of an effect. Wort in your kettle doesn't have much of its surface area (relative to its volume) exposed to light. But I could be completely wrong.

  5. oops. yeah, it's the hops. Since the compound that causes the skunking is the same that contributes bitterness to beer, i wonder if the overall amount of hops in the beer could matter any.

  6. I live in Oregon, so this is not a concern.

  7. No. It's practically impossible, for reasons others have said (bottles are essentially prisms for UV, kettles have comparatively little surface area, and skunking reactions only work on iso-alpha-acids, completely converted bittering units in final beer).

    Opinion speaking: skunking is, generally, one of those bugaboos that's easy to spot for beer snob neophytes. It's a sulfur compound, and a fresh, unfiltered lager will absolutely stink of sulfur (provided it's one of the southern german "aromatic" varieties). This is not necessarily a bad thing. It's a flavor profile like the "horsey" flavors of bretty belgian beers or the diacetyl and acetaldehyde of english cask ales.

    The skunky sulfur of heinken or pilsner urquell is merely a side effect of its packaging, more or less a feature that they know about and attempt to create and control. It complements the hop and yeast profile in a german/czech lager, much of which is lost in pasteurization and shipping.

    If you make one of those lagers yourself I guarantee you it's a product of the yeast, and it's not an "off flavor" any more than acetaldehyde in a "real ale" is. But it's easily spotted, and easily ranted upon.

  8. @Cerealdisobedience Sulfur is a distinct component of a fresh lager beer. However the "skunky" flavors to me that are extremely apparent in any stale old lager smell more of burnt rubber or band aids. It is usually paired with a oxidized character. And I do no think this complements anything in any beer. I avoid direct sunlight at all times. Especially once the wort it is in the carboy. In the kettle I wouldn't worry too much. Besides who wants to stand in the sun?

    Brew Strong Fellas.

  9. Speaking of Light Struck:

    The Perfect Martini by Luis Bunuel

    To provoke, or sustain, a reverie in a bar, you have to drink English gin, especially in the form of the dry martini. To be frank, given the primordial role in my life played by the dry martini, I think I really ought to give it at least a page. Like all cocktails, the martini, composed essentially of gin and a few drops of Noilly Prat, seems to have been an American invention. Connoisseurs who like their martinis very dry suggest simply allowing a ray of sunlight to shine through a bottle of Noilly Prat before it hits the bottle of gin. At a certain period in America it was said that the making of a dry martini should resemble the Immaculate Conception, for, as Saint Thomas Aquinas once noted, the generative power of the Holy Ghost pierced the Virgin's hymen "like a ray of sunlight through a window-leaving it unbroken."

    Another crucial recommendation is that the ice be so cold and hard that it won't melt, since nothing's worse than a watery martini. For those who are still with me, let me give you my personal recipe, the fruit of long experimentation and guaranteed to produce perfect results. The day before your guests arrive, put all the ingredients-glasses, gin, and shaker-in the refrigerator. Use a thermometer to make sure the ice is about twenty degrees below zero (centigrade). Don't take anything out until your friends arrive; then pour a few drops of Noilly Prat and half a demitasse spoon of Angostura bitters over the ice. Stir it, then pour it out, keeping only the ice, which retains a faint taste of both. Then pour straight gin over the ice, stir it again, and serve.

  10. I believe I recall reading somewhere that alcohol must be present in the equation along with the hop compounds to make the skunking chemical, so it's a during/after fermentation product. But I'm far from certain on this.

    For what it's worth I tend to brew in the sun quite a bit and have never experienced skunking in any of my beers. I've even tried to skunk bottles on purpose and been unsuccessful.

  11. Curiouser and curiouser. I expected this to be one of those obvious answers to which I was uniquely un-privy, but it seems not to be the case.

    To me, skunkiness is a radically different aroma than sulphur (either of the rotten eggs or struck-match variety). Skunk smells like ... skunk. Unlike DA, I've accidentally skunked my own bottled beer and it feels like a minor tragedy.

    A question deserving more consideration.

  12. Skunking (mercaptan) requires hops, fermented wort and UV.

    In wines, skunking (thiols) is a reaction between sulfer, yeast and UV.

    This reaction takes minutes. If this truly were a problem, there would be an abundance of problematic boils even in the cloud cover or shade. (UV rays bounce)

    Brew outside in full AZ sun. Never been dinged for skunked beer.

  13. Skunking is a KIND of sulfur compound, not the only one that will appear. Quoth "Principles of Brewing Science":

    "When iso-alpha-acids are exposed to light, photochemical cleavage takes place, yielding 3-methyl-2-butene-1-thiol. This compound is sulfur-based and has a pronounced skunky character. It is interesting that the sun-struck phenomenon competes with oxidation, in the sense that beers with high oxygen levels (or with a large amount of oxidized components) tend to be more resistant to photochemical transformations than beers in a reduced state."

    The end result being that despite any supposed resistance, Pilsener Urquell will taste decidedly un-fresh over here: crackery, paper like malt, muted hop aromas and flavors. It's a crime to happen to a beer like PU but that's probably just a side effect of the long travel time to get here, and not as much "skunking" itself, which as a phenomenon I think is highly over-reported.

    Frankly I think it's a little preposterous to assume a brewery like Heineken doesn't know what's going on inside those little green bottles.

  14. @andrew, I've gotten band-aids before in fresh lagers that were absolutely not oxidized or sun-struck. One time it came just from hops--100% tettnang. Tasted like a burnt tire to me, but everyone who tried it said it was fine.

    Differentiating a fresh lager and a stale PU is pretty easy, I think, but I'm not sure you could pick out the "skunk" in a fresh lager that's been intentionally light struck, just because of how much other sulfury stuff is in there. It would probably be more noticeable in an ale.

    In the mean time I will stand by my thesis: that the perils of skunking are vastly, vastly over-reported.

  15. Cereal, in my experience, beers in clear or green bottles are commonly lightstruck and noticeably skunky.

    An extreme example: I was at a daytime party where the host had a nice big tub of Coronas on ice. Unfortunately the tub was on a table in full direct sunlight. The were skunky as all hell. You could smell it from a distance or when someone walked by with an open bottle. Really bad. I quickly switched to G&Ts.

    On the other hand, I've never had a Corona in a can smell like skunk. The bottle makes all the difference.

  16. I've talked with a prof of brewing science at OSU and he told me that there needs to be flavins from the yeast + completely isomerized alpha acids(iso-alpha acids) + sunlight. Since theres no yeast in the boil i would imagine it would be close to impossible to have skunky wort. and like others have said i brew in full sun all the time. the prof also told me that a lot of the bigger breweries(corona) use hop oils that have been altered so that they cannot skunk. I left a corona in the sun and it tasted like a corona still. I also had a bottle of black butte porter that sat in a store window in full sunlight for about 7 years, and i tasted zero skunk flavor. thats my 2 cents, cheers!

  17. Interesting, albeit technical:

  18. Timdogg, I'm well aware of the ~science~ reasons behind what is happening. But I'm not sure you're getting what I'm saying: that this constant worry about light struck skunkiness is largely a narrative. A few points:

    -The "classic" BJCP examples of skunkiness are always lagers. I have never even heard of skunked ale, though according to the ~science~ it should be possible. The question for Jeff is what it was that he managed to skunk.

    -The traditional flavor of S. German lagers absolutely stinks of sulfur. The yeast itself smells like it, and any unfiltered style is going to stink like it as well. It is very pungent, some strains more than others. And as I said earlier, even some of the hops have a sulfur flavor.

    -Skunking is a sulfur compund, and sulfur is incredibly easy to spot. It's one of the big three that all newer brewers and "beer tasters" learn to judge (diacetyl, acetaldehyde), so it's constant appearance is vastly overreported. I am not convinced everyone who's described a beer as "skunky" has ever had a nice, full whiff of a skunk's asshole. I know I haven't. Such is the nature of tasting, and the same thing happens in wine for similar reasons. Not skunking itself but the phenomenon of "look how attuned my palate is, I can taste the [insert thing]"

    -Heineken is the flagship product of the flagship brewery of Heineken Intl, the third largest brewer in the world. You can say a lot about a mega industrial brewery, but "stupid" is not one. They undoubtedly employ entire teams of scientists and engineers. They most assuredly knows what happens to that beer when its put into the bottle and then sits on a grocery store shelf.

    -people like heineken. This is perhaps the most important one. Even just the other day at a brewing event, I brought some of my own lager, kellerbier-style, and someone came by and said that they really liked it because it tasted like Heineken. It's almost pavlovian: if you say that around brewers and beer tasters, someone is sure to groan "ugh, heineken, that is always so skunked." The Heineken fan was sharp, however; he was well aware that heineken was often skunked, and even tried it in several versions (the larger bottles, and those minikegs). But he liked neither of those as much as he did the smaller bottles. The reason, he assumed? More surface area to liquid, so more skunking. Which he actually liked.

    I know a single anecdote is hardly proof of anything, but I think the fact that Heineken and Corona continue to shatter sales (despite being almost twice as much per bottle as the domestic big three) is pretty good proof that people like the flavor. And the sulfur produced from the skunking is probably a part of that.

    A fresh lager will be a different kind of sulfury, but it will be sulfury. At least the ones with aromatic lager yeasts, the ones with the dustier type tend to throw off more green appley acetaldehyde, which is all over bud and miller. That's there intentionally too, by the way.

    Sorry for derailing an innocuous question, Jeff. (Cereal is me, blogger is giving me fits atm)

  19. Daniel, I get what you are saying. I just think it's a more common phenomenon than you do. No biggie.

    A couple of notes to your points: - I haven't closely sniffed a skunk's asshole, but I do know quite well what skunk smells like. Hiking, camping, and driving by roadkill have given me quite a few doses of this lovely aroma.
    - I get your point about skunk being a sulfur compound, but there is a difference in sulfur aroma and skunk smell. While certain lagers may inherently smell of sulfur, that is not the same smell as skunk. I don't find the two to be interchangeable at all in my perception.
    - Yes, people like skunky and/or sulfury Corona and Heineken. They sell a ton. No argument there. I am curious though; you say skunking is vastly overreported, but then you say people like the sulfur that comes from the skunking. Isn't that contradictory?
    - I don't think anyone said mega breweries were stupid.

    Anyhow, I'm not a scientist. I'm just going off what I have experienced. I know skunked beer when I smell/taste it.

    Maybe do a test. Get a can of Corona and a bottle of Corona. Put them both in direct sunlight for 20 minutes. Chill. Compare aroma/taste side by side. Maybe you'll experience a difference between the two, maybe you won't. I'm guessing you will.

  20. And yeah, sorry for hijacking the thread Jeff.

    Back on point, I brew in the Arizona sun. No problems with light struck wort.

  21. When I say "overreported" I mean the extreme examples, like that 20 minutes in a tub of ice in the sun caused all the beer to smell undeniably of skunk spray.

    I'm not sure it's even possible in 20 minutes because of temperature and dilution (both of which are factors in the speed of a reaction). But just empirically, I've never seen it go bad and I've seen it at a lot of parties served exactly like that. Modelo has carefully marketed corona as The Beach/summertime beer. Those are precisely the conditions that would cause this supposed cascading skunk smell. And I've never seen it or heard of it happening except from people on the internet.

    I'm not saying light struck beer doesn't exist, I just question whether it really smells as extreme as some people make out. Especially in a lager.

  22. It may be overreported to a certain extent Cereal, but a couple of points:
    -Quoting from the link I posted above "With a threshold of around 4 parts-per-trillion in beer, 3-MBT is among the most potent flavor compounds that can be found in beer; as such, it does not take much to ruin your beer. If you drink your beer from a pint glass on a sunny patio you may notice this flavor by the time you reach the bottom of the glass – that’s how quick this problem can arise."
    - Yes Corona is a beach beer, but it is typically served with a fresh cut/squeezed lime. There is a reason for that. It covers the skunk!