I was out and about this afternoon and had a clear plastic Go Cup of Hiddens Springs ZFG (Zero F’s Given), a local APA, for a little stroll on the Tampa River Walk. Normally I try to hide my hoppy beers from sunlight or don’t even order them when outside, but this beer, after 15 minutes in direct sunlight still smelled hoppy. No skunk. It made me think about the process a little bit. The reason for the name of the beer is that all of the hops are added post boil, which, according to calculators, shouldn’t provide bitterness. So here I was drinking a hoppy beer, bitter to my taste, that didn’t get light struck.
I guess there is something to this isomerization thing, eh? Late hop additions, to me, still add bitterness, but that bitterness, without isomerization, may not be susceptible to degradation from light.
Or is this just a fluke?
I think the perception of bitterness in late hopped beers comes from the tannins, not the alpha acids. See the Techniques column in the May/June BYO for more detail.
I thinks it’s also our brains tricking us: because we are conditioned to associate hop flavor with bitterness, we perceive it even if it’s not really there, or at least that it’s stronger than it really is.
There are also advanced hop products which are light stable and will not degrade into MBT to produce skunkiness.
There are other bittering compounds. This might help.
Light struck flavor comes from MBT. The original compound comes from hops but is not an alpha acid.
If the beer was hazy, possibly the haze provided some protection from the light. Prehaps it was a fluke.
This beer was clear and light enough that I can rule that out.
The article that Jeff posted above may explain where the bitterness comes from. I have to assume that the acids need to be isomerized in the boil in order to be light struck.
I certainly did not expect this and now I want to brew a no-boil-hop addition APA.
Don’t rule out tannins. I’ve learned some interesting things working with the American Nobles. Even though they were boiled, the AA is less than .5%. It tastes far more bitter than that number would account for. I think the tannins in no boil additions could play a big part in perceived bitterness.
Also don’t forget, HSA creates tannins as well, Herbstoffe to be exact.
Or to be less exact, since “Herbstoffe” just means “bitter substances,” and is the catch-all for all such in beer.
Only if you use google translate 
It more so translates to tannins in real German, and is always associated to in professional literature as a grain based bitterness that comes from oxidized mash polyphenols.
No, out of curiosity I just now actually tried Google translate. It’s totally screwed up (as usual,) thinks herb means “herb,” not “bitter” and just renders Herbstoffe as “herb substances”… [emoji849] Didn’t bother to see if it knows how to actually say “herb” (Kraut, of course.)
I was going on actual usage as well, I guess it varies in degree of specificity across the literature. In general in brewing literature (not only German,) I’ve observed that, though there has been some shift in emphasis, “bitter substances” has encompassed alpha and beta acids as well as tannins and even other bitter vegetable matter from hops and bitter substances from sources such as roasted malts, IOW anything that contributes to perceived and measurable bitterness – which is why an IBU value assumed to be equivalent to ppm iso-alpha acid is often quite misleading. This equivalence seems, unfortunately, to have become the general assumption nowadays, though 40 years ago the literature clearly distinguished " itterness Units," which accounted for the whole range, from measured iso-alpha acid levels, in both wort and beer. The significance was maybe better recognized then, when hops were often more degraded in storage, leaving isomerized oxidized beta acids and other substances to contribute a more significant portion of the bitterness even in the standard lagers of the day.
The hopping techniques coming into vogue now, that shift the impact away from iso-alpha again, may demand a reassessment of how bitterness is characterized and quantified. This thread is a perfect case in point.
Nice to see you back again, Beerery. Guess somebody has to poke you with a stick now and then. [emoji1]