Davis Grad + BS Chemistry here. I'm only 4.5 years late to the party on this one, but the krausen removal thing is something I've thought a lot about over the years, so here's what I have to add to the discussion.
Per John Palmer;
"A head of foamy krausen will form on top of the beer. The foam consists of yeast and wort proteins and is a light creamy color, with islands of green-brown gunk that collect and tend to adhere to the sides of the fermentor. The gunk is composed of extraneous wort protein, hop resins, and dead yeast. These compounds are very bitter and if stirred back into the wort, would result in harsh aftertastes. Fortunately these compounds are relatively insoluble and are typically removed by adhering to the sides of the fermentor as the krausen subsides. Harsh aftertastes are rarely, if ever, a problem."
So Palmer is saying (or at least WAS saying as of that publishing date) that krausen contains nothing good, but that it shouldn't be a concern since it's badness won't readily re-dissolve back into the beer. This strikes me as sound advice for any homebrewer, mainly saying that krausen is just part of the process of brewing, and the brewing process works, so don't worry about it. If something really isn't of concern, then it's reasonable to tell the regular Joe homebrewer to just ignore it because mucking about in your beer for a goal with no benefit can only hurt you.
But, the 99% correct answer to a question is not the "definitive" answer to the question. For that last 1% of the answer, I would direct your attention to one of the true greats of the American craft brewing scene, Matt Brynildson. Matt started out at Goose Island as a shiftie back in the mid 1990s, and quickly shot through the ranks to become their head brewer. He was then subsequently picked off by Firestone Walker out in California, where I believe he is still brewmaster. Matt was already there in the mid 2000's when I was entering the brewing field in the SF Bay area. In terms of what beers I was drinking in what eras, the summer of 2006 is one I'll never forget because that's the summer I spent drinking all the Firestone Walker Pale Ale I could get my hot little hands on. They still produce pales, and I don't live in CA anymore, but from the occasional comments I've seen about this beer over the years since, the later versions were all good but nothing ever matched the mid-2000 era product they simply called their "Pale Ale". And that beer remains to this day my personal "desert island beer", hands-down.
Reading up about FWB back then, I discovered that they used a very unusual brewing system called a Burton Union. I happened to know about this system because Dr Lewis described it to our class back at Davis. The basic idea is that the ferm vessels (traditionally wooden barrels) are laid on their sides next to each other in two long rows. Running between the rows at the height of the top of the vessels is a central tube. Each vessel has a tube running straight form the top of the barrel directly horizontally to the central tube. The overall arrangement is called a "street". One of the important design points of the street is that the individual "driveways" connecting to the middle "street" tube are immediately above the liquid level in the barrels. Basically, the barrel is on its side, it is filled with wort up to the very tippy-top, which means that there is virtually no headspace whatsoever. The driveway tube attaches to a hole in the side of the barrel, which since the barrel's on its side puts it at the highest point over the liquid. The fitting that attached the tube to the hole in the barrel is a 0-degree 90 elbow so the tube is more or less right at the liquid level. What this does therefore is force all the krausen into the driveway tube and out towards the street tube. (I have no idea how far the Krausen foam actually makes it down the tubes, but that's something I've always wondered about! FWB visit = bucket list item.)
In this way, nearly every bit of krausen is automatically removed from the beer in the barrel, no skimming needed. Now, Brynildson is a demi-god among brewers, and FWB was built to be a hang-the-expense all-the-way artisanal setup. So between those two facts, there's every other reason that that magical mid-2000s Pale would have been an awesome beer. But it wasn't just an awesome beer---it was a magnificent beer. The most magnificently
clean beer I've ever tasted. I've had a few other better-beer appreciators from CA agree with me on this, even 4, 6, 8 years after it (apparently) ceased to exist. One of them was a complete stranger on a barstool next to me in the midwest less than 2 years ago! So that's saying something about that beer.
Conclusion: Knowing what I know about the Burton Union brewhouse design, and knowing that the FWB guys set out to build one---the only one in N America at the time, I believe---it's hard for me not to think that it was this unusual process that made their mid-2000s Pale so special. And the defining feature of the Burton Union, near as I can tell, is that it removes all the krausen from the beer in a passive, closed, sanitary way. So in my opinion, while krausen clearly doesn't ruin beer or anything, its complete removal may be the difference between a very nice beer and an ultra-clean tasting beer. It seems likely to me that while the vast bulk of the sticky krausen is left behind on the fermenter walls, enough trace amounts of it pass through to the final product to stand between your tongue and the achievement of truly "clean" beer.
One last note, and this is pure speculation on my part. When Dr Lewis was describing the BU system for us, he mentioned that one of the reasons it is so rarely seen anywhere is that for whatever reason it apparently doesn't scale up. Up from what original/traditional size, I couldn't say for certain. If I had to venture a guess, I'd imagine a 19th-century brewhouse in the UK with a big long building housing a street of maybe 10 barrels on each side, those barrels being maybe the height of a man? In principle, you could have an arbitrarily long chain of barrels and scale it up in merely the horizontal direction I suppose. But that also means having to build an arbitrarily long climate-controlled building around the thing, so my sense is that being able to scale up only in one dimension means for all practical purposes, "not scalable". You need to be able to scale up in 3D to realize the gains, such as the larger and larger cylindro-conical fermenters that 20th century advances in metal fabrication made possible.
It is further possible (in my mind, probable) that FWB may well have realized they had built a veritable printing press for money with their beers by the mid-2000s, and decided to scale up anyway to cash in. This would account for why the subsequent Pales never quite measured up the famous earlier version. Perhaps Brynildson still produces small batches of the really good stuff on the Burton Union system for local distro only? You'd have to visit the brewery or talk to Matt I suppose. When breweries scale up and something is lost, but only a tiny handful of their devotees notice, it can become difficult to distinguish the straight dope from the marketing copy as the mists of time fold in around you.
Please remember that this is all purely speculative, I have zero evidence for any of these musings of mine. If anybody has some inside baseball knowledge that expands, negates, or contradicts my hypotheses, I'd be happy to stand corrected on any of it.
In Summation: I don't know if this will qualify as definitive by Jakemo's standards, but I think it substantially adds to the thread. Hopefully others will subsequently stumble across it like I did, and throw in whatever comments, corrections, or insights they can add to mine. A truly exhaustive treatment of the implications of krausen removal to the taste of the final product would necessarily include a fine-grained analysis of the krausen's physical constituents, their properties, before-and-after comparisons of measured levels of the various compounds in the wort and the finished beer, etc. I currently have access to a local university's library portal, and a few of my less-than-expert searches of the academic literature turned up nothing interesting when I searched for krausen analysis. Like many other aspects of brewing that we might be interested in reading up on, it's very likely that most of the good research that's been done on this is still proprietary knowledge that the big companies paid top-dollar to do in-house, so you can't totally blame them for not just going full Jonas Salk with it.
Brynildson's bio page from FWB company website:
http://www.firestonebeer.com/brewery/matt-brynildson.php
I'm concerned that I may have lost a significant amount of good hop oils through the blowoff.
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