Head Protein life span

I've heard Jamil say from some of the BN podcasts that head forming proteins only form once, then they are destroyed. Does anyone know the science behind this? Basically I'm questioning whether its BS or if someone has actually looked at the lifespan of the head forming proteins.

This thread is worth a read. Essentially, I think it's BS. They get reabsorbed into solution... at least post-fermentation.

Excellent thread. Thanks for the reference and the experiment.

blue800 said:

I've heard Jamil say from some of the BN podcasts that head forming proteins only form once, then they are destroyed. Does anyone know the science behind this?

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Polypeptides, proteins, and iso-alpha-acids all combine to form a good beer head. This should help explain the importance of protein in beer foam. From Beer: quality, safety and nutritional aspects By E. Denise Baxter, Paul S. Hughes:

Foaming during beer production can lead to the irreversible loss of foam-active species. Irreversible denaturation of proteins, a process perhaps essential to the formation of beer foam, generally reduces protein solubility. Thus foaming will result in a loss of a proportion of foam-active proteins from the bulk beer. Paradoxically, the use of silicone antifoam agents during fermentation is beneficial to final beer foam stability....This is on account of the suppression of foam head during fermentation, with attendant reduced losses of protein.

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menschmaschine said:

This thread is worth a read. Essentially, I think it's BS. They get reabsorbed into solution... at least post-fermentation.

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You're only partially correct. Some of the essential foam forming agents (e.g., polypeptides and iso-alpha-acids) are reabsorbed post-fermentation (i.e., not lost to krausen deposits) but the foam positive proteins do NOT get reabsorbed since they are, well, denatured. A subtle yet important distinction.

So...Yes, as much as I dislike his approach to brewing science, Jamil is correct in saying that an essential foam positive agent (protein) is inherently destroyed upon foam creation.

lamarguy said:

You're only partially correct. Some of the essential foam forming agents (e.g., polypeptides and iso-alpha-acids) are reabsorbed post-fermentation (i.e., not lost to krausen deposits) but the foam positive proteins do NOT get reabsorbed since they are, well, denatured. A subtle yet important distinction.

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Until I see a plausible scientific explanation of this, I'm going to question it. How do foam positive proteins become denatured? What happens to their constituent proteins/amino acids? Why would some proteins get reabsorbed and others not? For that matter, why would some proteins denature and others not?

menschmaschine said:

For that matter, why would some proteins denature and others not?

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Different proteins denature under different circumstances. This is readily observed in cooking. Egg whites, fish and red meat proteins denature and different temperatures when heat is the catalyst for denaturing. Fish protein can be denatured via low pH (ceviche) more readily than red meat protein.

Perhaps more important is that some proteins once denatured will never return to their native state, others will.

Now, I'm no chemist and I can't exhaustively explain what is going on in beer with regards to foam positive proteins, but I have to point out that you aren't exhaustively justifying your position any more than Jamil, me or Lamarguy are ours. Lamarguy's source authors are chemists so at least we have appeal to authority on our side.

menschmaschine said:

Until I see a plausible scientific explanation of this, I'm going to question it.

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I'm not a chemist, so I can't help answer all of your questions but I can present supporting evidence that foam-positive proteins are denatured upon foam creation.

For example, take beating an egg white:

All proteins, including those in egg white, are made of long chains of amino acids which are similar to beads on a string. In a raw egg, these chains are raveled up in a specifically arranged compact mass. Chemical bonds and interactions between the amino acids within each protein hold this mass in a specific shape and stop it from unraveling...

The physical stress of beating the egg white can create a foam. There are two types of physical stress caused by the beating of the egg whites with a whisk, the first being that the whisk drags the liquid through itself creating a force that unfolds the protein molecules. This process is called denaturation. The second stress comes from the mixing of air into the whites which causes the proteins to come out of their natural state. These denatured proteins gather together where the air and water meet and create multiple bonds with the other unraveled proteins and thus becomes a foam holding the incorporated air into place.

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If you'd like a detailed explanation for exactly which proteins are denatured, this should be a good paper to read - Protein Denaturation in Foam: II. Surface Activity and Conformational Change.

As part of a study of protein denaturation in foam we have measured the surface tension and the changes in protein structure occurring at the interface for lysozyme, pepsin, BSA, YADH, IgG, and catalase. The apparent CMC values were found to be dependent on the size and rigidity of the molecule. The variability of protein damage at a gas–liquid interface in foam was assessed using these proteins. The foams were produced under controlled conditions in a bubble column and were found to induce conformational changes in the protein molecules, but no fragmentation or disassociation of subunits occurred. Tertiary structural changes were detected in all the proteins studied, with some proteins forming aggregates. For pepsin, the secondary structure was also found to be altered. Enzyme solutions were used to determine the degree of biological activity retained after foaming for proteins with different structural characteristics. The more rigid proteins were found to display a low surface activity and a low degree of damage in foam. Pepsin suffered the highest rate of damage, which is thought to be a result of its inability to refold following denaturation.

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That's interesting, lamarguy. The 2nd article abstract shows that there is a mechanism for protein denaturation in foam at a liquid gas interface. It also shows that there is variation among proteins regarding how much, if at all, they denature in foam. Here are the proteins from the study:

lysozyme = antimicrobial enzyme- common in eggwhite
pepsin = proteolytic enzyme
BSA = bovine serum albumin
YADH = yeast alcohol dehydrogenase (enzyme - interconverts alcohols to aldehydes and ketones)
IgG = anti-body in blood
catalase = enzyme converting H2O2 to H2O and O2.

So none of these specifically relate to beer foam. I find this statement interesting:

The more rigid proteins were found to display a low surface activity and a low degree of damage in foam.

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I wonder how "rigid" are beer foam proteins?

It's good to finally see a potentially plausible explanation. I can't, however, say that I believe it in regards to beer foam until I see a specific study on it. It just doesn't add up. Why don't those who produce foam from aeration see a significant decrease in beer foam stability? Why did pjj2ba's experiment in the other thread have the results it did?

I tend to think that these proteins get "used up" is mostly fake. I remember reading a scientific article where, in order to study the head-forming proteins, they bubbled gas into the beer, scraped off the foam, put it in water, bubble gas into that and so on until they had clean proteins. Why would that work if these proteins denature so easily?

Denaturing is not always an end state!!!! More than just a few proteins can refold themselves after being denatured. It partly depends on what forces denatured the protein in the first place - heat, whipping, pH, salt concentration - and the other components of the solution/matrix. Also, many of the foam positive proteins, have been modified by the mashing process and fermentation so they behave differently from the native forms.

I don't know specifically about the proteins in beer, but I do know about proteins in plants. Some of these can definitely re-nature after being denatured. I recall that one of the foam positive protein is a HSP (heat shock protein). These come in a variety of sizes. These proteins still are not well understood, but one function that has been shown is to help to re-nature other proteins, typically in response to stresses

I think that as long as the foam proteins make it into the fermentor, then you are good to go. If you have a lot of foaming beforehand and don't let it reabsorb and leave it behind, then you are robbing yourself of potential foam. I've got some extra wort right now, maybe I'll half fill some clear glass bottles, autoclave and then SEAL them and redo the shake experiment. In my previous experiment, the flasks were just covered with foil, so maybe the air exposure had an influence

I suspect another factor here that is very significant to consider is the RATE of (permanent) denaturation. I suspect that just shaking a vessel of beer will lead to a very low rate of denaturation. It takes quite a bit of energy to whip up egg whites, and we certainly aren't approaching that in any way by merely shaking a carboy or keg.

I see the point that protein damage is possible and could be detrimental to head formation and retention, but one should also consider: HOW LIKELY is it?

My $.02.

So, between shaking my carboy and getting a blow off, I'll never see a head on my current batch of beer I guess. You would think all of these headless beers would have raised questions before now. Unless..........

Hermit said:

So, between shaking my carboy and getting a blow off, I'll never see a head on my current batch of beer I guess. You would think all of these headless beers would have raised questions before now. Unless..........

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I think the "science" forum should exist free of posts that do nothing but construct straw men.

remilard said:

I think the "science" forum should exist free of posts that do nothing but construct straw men.

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Not sure what you are getting at here, but a lot of science has to do with explaining observable behavior. If people shaking their carboys and getting massive blow off haven't had problems with head on their beer then the 'problem' of single use proteins is more theoretical than practical isn't it? Jamil says he doesn't like to use air because of this 'problem'. This is the basis of the thread yet plenty of people do this without problem.

remilard said:

I think the "science" forum should exist free of posts that do nothing but construct straw men.

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How was that a straw man? He has not modified or changed the premise of the problem in any way. He perhaps exaggerated the effects (by saying "NO head"), but we know what he means, and I think he's right to point this out.

rocketman768 said:

How was that a straw man? He has not modified or changed the premise of the problem in any way.

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The original proposition is:

blue800 said:

head forming proteins only form once, then they are destroyed

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The strawman is:

Hermit said:

between shaking my carboy and getting a blow off, I'll never see a head on my beer

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These are two separate concerns that are only casually related. Beer foam is much more involved than just protein participation at the liquid-gas barrier and making casual generalizations just detracts from the discussion.

So, please...Back on topic!

While this paper doesn't specifically address protein denaturation, it does explain the mechanics of foam creation and stability. Definitely a worthwhile read.

The Relative Significance of Physics and Chemistry for Beer Foam Excellence: Theory and Practice by C.W. Bamforth

OK, yesterday I set up some bottles of yeast media (ie. leftover wort) and autoclaved them (I use it to start yeast in test tubes). I've set one aside and I'll shake it every day and see what happens. Actually one thing I've already noticed is the difference compared to finished beer. The foam is VERY stable. I shook the bottle about 4 hrs ago and got maybe 1.5" of foam. It still has ~0.5" of foam. I bet there will probably still be foam left tomorrow morning. Thinking back, I saw the same thing the last time I did this. So then something is definitely changing the foam behavior during fermentation. Of course there is a lot more sugar in wort, than in finished beer. I'm not sure how much of a role that would play

pjj2ba said:

Of course there is a lot more sugar in wort, than in finished beer. I'm not sure how much of a role that would play

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Yes, I suppose this could be an issue. The extra viscosity and the absence of alcohol will both facilitate head retention. It may become difficult to generalize results from a wort experiment to actual beer -- hard to say.

pjj2ba said:

Actually one thing I've already noticed is the difference compared to finished beer. The foam is VERY stable...Thinking back, I saw the same thing the last time I did this. So then something is definitely changing the foam behavior during fermentation.

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According to the literature, several fermentation by-products negatively affect beer head, including (ranked from highest to lowest):

1. Fusel alcohols
2. Unsaturated fatty acids (e.g., linoleic acid from break material)
3. Ethanol (lowers surface tension)
4. Loss of iso-alpha-acids (due to yeast flocculation)

So, it would make sense to only experiment with fermented beer to ensure the anti-head agents are present.

Maybe the more important question is; why don't we actually see what the science says we should see in our beer regarding this? Because we don't really see this 'loss' of beer foam in our beer do we? My uber-simple experiment showed no difference in the shaken-every-day-for-a-month growler vs. the left-to-rest growler. It almost seems as if the cart was put before the horse. That is, we got an explanation of why we lose beer foam positive compounds when nobody ever complained of losing beer foam positive compounds...they just complained of a lack of head on their homebrew, which is totally different (their homebrew probably didn't have the right foam positive stuff to begin with but it certainly wasn't because they 'used it all up').

SpanishCastleAle said:

we got an explanation of why we lose beer foam positive compounds when nobody ever complained of losing beer foam positive compounds...they just complained of a lack of head on their homebrew, which is totally different

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You lost me. No one complained about losing beer head, the OP simply questioned the science behind Jamil's statement that proteins are destroyed upon foam creation.

blue800 said:

I've heard Jamil say from some of the BN podcasts that head forming proteins only form once, then they are destroyed. Does anyone know the science behind this?

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We've since learned that, at least, some essential foam-positive proteins are denatured upon foam creation. The cited authors assert that protein denaturation is an end state and, as such, excessive foaming will lead to a reduction in essential foam-positive proteins. The end result being a beer that does not form a good head and/or has poor foam stability.

I believe the only remaining question is - During foam creation, is foam-positive protein denaturation an end state?

lamarguy said:

You lost me. No one complained about losing beer head, the OP simply questioned the science behind Jamil's statement that proteins are destroyed upon foam creation.

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I did make a leap there. You have to back even further. The way the sequence usually works is that someone complains that they don't have good head formation/retention. Then the explanation of how we lose foam positive compounds comes in (there was an old Pro Brewer thread, mentioned in at least one of the related HBT threads, where this happened and a member named Cargill Malt responded with the 'lost foam' hypothesis). My thinking is that the original lack of head wasn't because they 'used it all up'. My hypothesis is that only in very rare cases do homebrewers lack good head because they 'used it all up'. In almost all cases it's 'something else'.

We all ferment our beer and create a TON of foam, but we still get clouds of fluffy foam. We have massive blowoffs but we still get mounds of merengue. We shake a beer in a growler with extra headspace every day for a month, but still get head just as good as the non-shaken growler. We just don't experience this 'loss of foam' to any significant degree. So my question was; since we have all this scientific explanation for why we should experience all this loss of foam, why don't we?

SpanishCastleAle said:

Someone complains that they don't have good head formation/retention. My thinking is that the original lack of head wasn't because they 'used it all up'. My hypothesis is that only in very rare cases do homebrewers lack good head because they 'used it all up'.

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Yes, that is an entirely different problem. So far, we've been discussing how a wort with excellent foaming potential might lose some of that potential due to excessive foaming during fermentation, packaging, handling, and transport (i.e., due to irreversible protein denaturation).

I believe you would like to discuss how protein denaturation affects a wort/beer with poor foaming potential. I can't imagine protein denaturation being more or less of a problem in beers with poor initial foaming potential. I mentioned earlier in this thread that a healthy fermentation is essential to forming a good head. Yeast by-products from a poor fermentation will quickly kill the potential for a head. We can probably agree that many homebrewers struggle with poor fermentation practices (e.g., underpitching, temperature control, poor sanitation, etc.).

SpanishCastleAle said:

So my question was; since we have all this scientific explanation for why we should experience all this loss of foam, why don't we?

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I believe it has to do with our ability, as homebrewers, to control most (if not all) environmental factors for making beer. That is both our greatest strength and greatest weakness.

Much of the literature and studies comes from the commercial brewing industry. They lose control of the beer once it leaves the brewery; often lending the beer to severe mechanical abuse and temperature extremes. This stresses the beer and can lead to eventualities such as:

1. Loss of a once excellent head (due to mechanical abuse leading to excessive protein denaturation)
2. Haze formation in a once brilliant beer (from a combination of mechanical abuse and temperature extremes)

If you've had the chance to read some of Charlie Bamforth's papers, he talks about these eventualities and what brewery practices can help slow them. Once of these "best" practices is to avoid excessive foaming during beer production. Of course, we can argue what is considered "excessive".

SpanishCastleAle said:

I did make a leap there. You have to back even further. The way the sequence usually works is .......

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In this case it was a podcast where Jamil insists he must use his O2 to oxygenate his wort because an aquarium pump will use up the head forming proteins. This in spite of the copious evidence to the contrary.

blue800 said:

I've heard Jamil say from some of the BN podcasts that head forming proteins only form once, then they are destroyed. Does anyone know the science behind this? Basically I'm questioning whether its BS or if someone has actually looked at the lifespan of the head forming proteins.

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Ah yes, I'm always thinking purely from the homebrewers perspective. I rarely drink beer I didn't brew.

But I have real hard time believing that packaged beers lose head formation/retention due to excessive foam formation in the bottle. I'm sure they lose head somehow, that's easy enough to observe. And I believe that they may have been mistreated. But just think of how 'immune' our beer seems to be regarding this 'lost foam'. It just doesn't happen to any significant degree even if we try to make it happen. So it's hard to imagine what it would take to get a bottled, commercial beer to lose foam due to excessive handling/shaking/foaming. That must be one long, bumpy train ride...to the moon and back.

Which brings up a question: Did the East India folks also complain of 'no head' on their beer? Surely that long trip created a ton of foam.

wow...good discussion here.

After looking at that first paper, they show that a portion of each protein (they used generic molecular biology proteins) is lost during foam creation and that in the formation of the foam pulls the majority of each checked protein out of the beer to build the foam. Therefore if the particular head proteins in beer degraded even at 30%, I would buy that foam is limited. This agrees (restates) with Flyguy's statement that the creation of head during the life of the beer will degrade the protein slightly.

But looking at SpanishCastleAle's expreriment shows that the head proteins in his particular beer (assuming those proteins are degrading) are degraded slowly if he can shake the piss out of the beer every day for a month and still get equivalent head formation.

It would be nice to see some other HBTers repeat that expt...maybe I'll try that.

Hmmmmm, maybe the key thing that we haven't considered is the role of Oxygen. The amino acid methionine is fairly susceptible to oxidation. Oxidation can lead to denaturation, which in this case could be irreversible. There is fairly recent evidence that proteins have evolved to contain extra methionine residues that can act as "sacrificial lambs" to protect the key amino acids around the active site from oxidation. Once the methionines have all be oxidized, then the other amino acids will be attacked, and ultimately lead to the destruction (recycling) of the protein. Plants and animals have an enzyme that will convert the oxidized methionine back to it's normal state (I studied this enzyme in plants for a couple of years) This enzyme would be active in yeast, but not in the wort or finished beer.

The same could be true for the foam positive compounds in hops. The presence of 02 causing loss of them via oxidation. This would suggest than that a capped beer could be shaken over and over again and not lose any foam. Expose it to some O2 and the story would be different. Of course my previous shake experiment was not sealed - but was unfermented wort.