The Science Of Beer Foam
    By Hank Campbell | August 31st 2012 02:57 PM | 33 comments | Print | E-mail | Track Comments
    About Hank

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    I'm not much of a drinker, never have been. I have always assumed it was because I did competitive athletics until I was about 25, which means I was outside the age where you 'learn' to like the taste of alcohol, so I never picked it up.

    Older now, I can drink a beer socially and I sometimes drink a glass of red wine because the consensus says it is good for you in moderation, but I am still not really a drinker.

    However, I love to learn about drinking.  I have giant tomes on wine, whole books on Scotch, I have a 2008 4-pack of Bourbon County in my garage 'beer fridge' (yes, I have a  beer refrigerator in the garage that holds almost everything but beer) that I am waiting to crack open because it supposedly 'ages' up to 5 years.  Beer that ages like wine.  I am a sucker for that.

    You can imagine how excited I was getting a copy of "Foam" by UC Davis professor Charles W. Bamforth, courtesy of the American Society of Brewing Chemists.  This is volume one - of six - about beer. That means it will essentially be the beer equivalent of William Shirer's "The Rise and Fall of the Third Reich", except it has no Nazis. And it is about beer.  Okay, maybe that was not the best comparison but people who have read that book know what I am talking about.  It is everything you could ever want to know.  And so it is with "Foam".  This is basically the best beer foam user manual you are going to get. Like all good user manuals, it even has a Troubeshooting Guide. 

    Want to learn about beer foam without going to school for 8 years?  FOAM is for you.

    Some book about whacking Osama bin Laden (and, less likely, a book called Science Left Behind) is going to be a bestseller in September but this should be instead.  What do people care more about, a dead terrorist or beer? Exactly. Professor Bamforth can't be thrilled I have invoked Nazis and terrorists in a review of his book but that is how culturally significant I think beer - and therefore beer foam - is.

    You see, I have always felt like beer foam is underrated.  It turns out I am not alone and Bamforth's book covers the gamut of the field - from psychology to physics to chemistry and engineering. 

    First, some psychology.  Part of enjoying anything, be it beer or a restaurant or awesome science sites, is presentation.  My wife is a terrific cook but it will not taste as good if my sons are fighting over who gets to marry that girl on the iCarly TV show, while a cozy winter lodge and a fireplace while someone else watches our children fight over Miranda Cosgrove makes even canned chili appealing.

    Part of enjoying beer is the visual aspect.  Social psychologists will say beer evolved to match what people like while evolutionary psychologists will say we evolved to like the beer that gets us a date.  Social psychologists win this one because women, that evolutionary target of men, who are the primary drinkers, don't play by the rules regarding beer foam they should play by if biology were the issue.

    Beer foam: The Gender Gap

    Does beer foam need some sort of outreach program?  Are women biased against it?  

    Maybe. It might explain why men drink more beer.  Beer is a total package, it has an aesthetic and a taste but color and foam are the most striking things people first notice in beer.  What foam is left over on the glass after the beer, the 'lacing' as experts call it, impacts the perception also. As I said, beer evolved to match what people like - because people buy what they like, not what is available, over the long haul - and people seem to like 'the middle' when it comes to foam; not too much and not too little or else it gives them ideas about its quality and even its alcohol content.  But not all people. While all people had a preference for how 'clean' they like the glass to be when finished (and therefore how much lacing) there was a real gender difference in how much lacing women wanted.

    Conclusion: It may be that the market for lace in beer, much like in a Victoria's Secret, is not women at all.

    Are the Scottish anti-science about beer foam?

    Sure, the northern Europeans are most famous for beer but Scottish people drink too.  Celtic fans need to do something while waiting for the match to be over so they can headbutt Rangers fans and then kick them when they are on the ground, and whisky is too expensive to drink for two hours.  

    The science is settled, the consensus is clear; foam matters, it is a harbinger of beer to come. Yet not everyone accepts its importance.  The wrong foam was perceived by Americans as being lower quality and even less alcoholic.  They also felt like more foam meant it came from a dirtier glass. That last part is incorrect but Americans were at least thinking about the foam. The Scottish cared about foam the least of all countries tested. 

    Conclusion: the Scottish are anti-science about beer foam. At least they got haggis right.

    The Physics and Chemistry of Beer Foam

    I can't go into too much detail here because we are talking about a 60 page book on beer foam in which not a single paragraph is wasted.  I would have to write 120 pages to cover everything. You should obviously just buy the book if you want to know the true nuts and bolts of foam.

    I can tell you that, were it legal, beer foam would be a great way to teach high school students about science.  There is a science reason 1,500,000 bubbles in the foam of a glass of beer play so nicely and that reason is surface tension and surface-active molecules. The nucleation we have come to know and love about beer foam is a vital aspect so by all means get annoyed if a bartender or waiter thinks he is doing you a favor gently pouring your brew down the side of a glass.  He is cheating both you and science. Bamforth cleverly relates viscosity in beer to baseball fans in Wrigley Field, a metaphor you can appreciate if you like teams that cannot win Big Games.

    These beer guys know applied chemistry in a way that is dizzying so they do what they can to mitigate anti-science waiters pouring beer down the side of the glass. That means foam-stabilizing materials and terms like proteolysis.  Trust me, they care about foam so you don't have to.

    And they get cool equipment. 

    The equipment used in their beer lacing index.  Credit: Dr. Evan Evans

    How to get the best foam

    If you are a serious beer foam person - and I am after reading this book, even if for no other reason than to annoy my friends - and making your own beer, you can get a lot of benefit out of his Troubleshooting Guide in Chapter 7.  Yes, this really is a beer foam user's manual.

    Otherwise, you likely just want to optimize the foam of the beer you just got.  Here are some handy tips:

    1) Consider a foam-nucleating glass. They mention Headmaster and Head Keeper as go-to trade names. I have one on my birthday list!

    2) Watch your detergent.  A beer, therefore including the foam, has already been optimized in regards to lipids (fats) so adding your own is not a great idea.  Combining the many polypeptides and peptides in beer with external lipids in detergents means lousy foam in your beer because detergent is designed to make its own foam. Whether you can see it or not, a fat-based detergent will leave a film on the glass, which means duds for suds and beer will go flatter faster.

    3) Don't use your beer glass for anything else. Do you use your coffee mug for soup? Of course not. Same with beer.  And don't dry it with a towel either.

    The beer used in my field testing:

    I told Drs. Bamforth and Evans I wanted to crack open one of those 2008 Bourbon County's from paragraph one to write this article but that is an 'event' beer and it needs to have more people over.  Impossible on a Friday morning in Folsom - Intel people won't start drinking until 2 PM.  So an update on that will have to come later.

    More reading:

    Evans, D.E., and Bamforth, C.W. (2009) Beer foam: achieving a suitable head, in “Handbook of alcoholic beverages: Beer, a quality perspective” edited by Bamforth, C.W., Russell, I., and Stewart, G.G., Elsevier Burlington MA, pp 1-60

    Evans, D.E., and Newman, R. (2009) Its better in a glass! The Brewer and Distiller International 5(10): 26-29.


    Off topic here, but followed the link to your book Science Left Behind. Based on the blurb sounds like the type of book I want to read. Definitely the left has kooky ideas too. But did they ever enshrine them in their political platform? To get elected in the GOP you have to subscribe to creationism, and that warming is not happening/is happening but not human's fault, just to name two examples. I can't think of any similar 'requirements' for Democrats. Which is why I'll read your book....I'm not American but I do enjoy needling my American friends of both parties. Unfortunately, in the last few years the Repubs have been making it far too easy to ridicule them. Hope your book gives me a bit more ammunition for my democrat friends....they've been getting off too easy at least on the science front.

    Btw, it is all good natured needling....they poke fun at our politics and I have to agree we have some reality impaired politicians too.

    Sorry I didn't comment about beer, but it isn't my interest...the science thing is though. Will get your book.

    Thanks, though the book isn't about Democrats, it is about progressives. 

    On your points, the DNC will have an invocation just like the RNC did and creationism is as much a part of the platform as it is for Republicans, that I can see.  The Democrats say they are the party of black people and 82% of black people deny evolution so Democrats are not making atheism part of their platform any time soon.  A Democrat was the one who took a rifle and shot the Cap and Trade bill, not a Republican - and the left blocks every solar power plant with lawsuits, not the right.   Both sides have their anti-science crackpottery and, science and science media being skewed as it is, the craziness of the right is documented every election season but no one tackles the left.

    So we will either do okay or have a giant sales flop because we are going after people on the kooky anti-science fringe - but we don't rant about liberals or Democrats so there is no red meat for the hard right, and they want red meat during election season. 

    I agree Republicans have terrible PR in science but, again, the media is not balanced in science the way it is in political coverage. If only evolution and global warming were the limit of anti-science beliefs, we'd be okay - but in the short term, anti-vaccine, anti-agricultural, etc. are far more dangerous.  
    "To get elected in the GOP you have to subscribe to creationism"

    John McCain and Mitt Romney both said they accepted evolution.

    We hope you enjoy the book!

    All very interesting, this yet another book from the dodderingly tedious faculty of my old brewing grad school - hats off - UCDavis. But as with all things scientific, wherever a cause generates an effect, the converse is true - which is to say every effect has a cause. So it is with foam - the effect doesn't just happen to be there because it's on top of a glass of beer. Something is in the beer to trap the bubbles of CO2 released when the beer goes in the glass. A natural feature of "malted" grains used for centuries to make beer, foam can also be achieved using more cost-effective, which is to say cost-reduced, ingredients. Wonder why American beers taste so bland? Well, the foam is there but the components that give beer its flavor aren't. Rice costs much less than barley, as does beet sugar - and such cheap adjuncts can be used to make beer wort which will ferment just as easily as one made entirely of barley malt. But as for the flavor, well just have yourself a Miller lite and enjoy if that's your style! Talk all you want about the interesting science of foam, but it's the economics that really drive the use of that science, and only a beer drinker would appreciate what is lost in the process. Maybe next time better stick to writing about something you have a taste for.

    I always have a disconnect with these purist arguments because I think people of all incomes should have a beer if they want, without sanctimony.  I've never had a Miller Lite but I have tapes of all four Steelers Super Bowls from the 1970s, which include the commercials, and I can tell you at least one has a light beer commercial. And they were not using beet sugar then, they were addressing a market.

    Science may not have made a great light beer, or a great cheep beer - yet - but that is like criticizing Henry Ford because he did not make a car that get 200 MPG.  A business that makes something perfect no one can buy is out of business, a business that makes something terrible and counts on price is out of business.  But over time, quality goes up and the price, at least as a percentage of GDP, will not. That is a win for everyone.

    Since you are part of the rich 1% that can afford any beer, or make your own, I salute you - truly, I appreciate the effort and the time - but I also dig that people are devoting their lives to enthusiastically trying to get the best experience for the most people at the lowest cost.  In America, we are claiming we can do that with health care but, yeah, if we can't do it with beer or food, it is smart to be skeptical it can be done with something really complicated and expensive.
    " And they were not using beet sugar then, they were addressing a market."
    How exactly would you know this, or doesn't it matter? Alcohol beverages aren't subject to ingredient statements, and there are a great many "foam stabilizers" grandfathered into the BATF regs . You frankly have NO idea what you're talking about, except that if the consumer is okay with drinking it and can afford it, fine. Right in line with the marketing of everything else manufactured by the food industry.

    "Science may not have made a great light beer, or a great cheep beer - yet - but that is like criticizing Henry Ford because he did not make a car that get 200 MPG." Well, the industry has certainly had a long time to develop this and so far the results just keep getting worse. But no worse than the rest of the products coming out of Big Food. So what is the stuff that makes foam? In high malt beers, it's grain protein (which by the way digests so you don't see it in your urine) but synthetic stabilizers are usually cobalt compounds (cheaper than the organic ones of earlier days such as Atmos 3000) and these don't digest - so when you're looking down at the urinal late in the evening, you may notice the foaming effect isn't limited to beer (don't worry, this particular foamy urine doesn't mean you have multiple myeloma). Cobalt is toxic (carcinogenic to be exact), but remember the industry isn't subject to FDA regs so ingredients that go into beer don't have to pass the same scrutiny as the rest of our food supply.

    So to cut to the chase, no I don't have a lot of money to buy what I want so I'm not in the 1% (does your column always turn political? I note comments go that direction). And it's a bore to make beer at home. But I've worked in Europe and make a living in the food industry, so I know good from bad (yeah, I know it's subjective but these issues go back a long way - post WWii to be exact when food engineering and the food flavor profile made food quality a matter of the lowest common denominator).

    So what you're saying is that it's okay to let mass market sales determine good and bad and this is not an approach, really, that's all that original, nor anything to be all that proud of.

    So what you're saying is that it's okay to let mass market sales determine good and bad and this is not an approach, really, that's all that original, nor anything to be all that proud of.
    Not sure if this is supposed to be amateur philosophy or amateur economics but I hope you know more about beer.  

    Yes, I absolutely believe that people should buy what beer they want to buy and companies should sell beer people want to buy.  That includes good beer and bad beer, expensive and cheap. The problem with your approach is its totalitarianism; you want to suppress dissent and diversity and make everyone into cookie-cutter replicas of your weird belief system.  I do not. If that is political to you, okay.  Stop acting like a food nazi if you don't want people to treat you like you are one.
    I get it now - your column is really about politics, which is to say about attaining consensual approval from the mass market - in this case not for ideas but for taste. So my mistake as a techie was thinking there was any serious interest in discussing beer foam here. It also makes sense that being a political writer you couldn't resist having a bit of fun mischaracterizing my point of view as that of a "food nazi". So if I get your drift, the American market prefers lousy beer, so hooray for our breweries that they can make lousy beer so well. To make better beer which is to say more like that made in the rest of the world - would be something only elite consumers could afford. But in fact that's quite wrong. What I've found in working a good many years in the third world is that food, wine and maybe especially something like beer, is very good in the poorest countries where widespread use of modern food science has yet to arrive. Why? Because it takes money to use technology, and mostly this goes to make things taste lousy - technology is used mainly to reduce costs. The quality achievement of factory food is that it's uniform and doesn't spoil during extended transit and storage. Since serving the mass market is all you require of a manufacturer (and I assume you think the mass market actually determines what Big Food puts in cans or bottles, when it is in fact the other way around), then making dependably insipid beer that doesn't get any worse after a few months is an achievement. Other than water, milk and fresh juice, beer and wine are the oldest beverages - their production has historically been a matter of craft, not science. It says something about the US, that our beer is inferior, and more expensive, compared with that made in countries such as Salvador, or throughout Africa. What it says is that our taste for things has been manipulated by technology to prefer the inferior. What else have we lost?

    Hi Hank

    I am a beer drinker. Beer should be made from malted barley and hops. Nothing else. But that's just my opinion. You say that science may not have made a great light beer. Actually some genius managed to make a light beer with 2,4% alcohol from only malted barley and hops. NO additives, sugar beets or any other weird stuff that does not belong in beer. Not only does it taste great, it has half the alcohol content of normal beer as well as a third less calories. It cost the same as you average beer too. It is brewed in Namibia, Africa. One final and very satisfying fact, it laces the glass perfectly and never run out of bubbles!

    I get your point - hey, I am making pasta from scratch today and a whole lot of people think buying it in a store is just fine.  This morning I made my coffee in a Chemex pot, no automatic drip or pods for me.  And I pity people who use tea bags.

    Yet I think instant grits are fine.  Basically, it is all subjective.  You are really not getting a terrible cup of tea if you use a tea bag.  So it goes with beer.  It has a market for all kinds.  

    To do it just one way would be to ghetto-ize the world into those who have beer and those who do not, and those without would be the poorest people.
    Let them make the fake beer. Just have them call it something else. Like a fake iphone is called a Samsung.

    That is just your opinion, that beer should be made from nothing but malted barley and hops (and one would assume, water and yeast as well). I have made 94 batches of beer or ale and the most interesting were the 20 or 25 made without hops. I bittered them with herbs like yarrow, heather, or wormwood. The resulting fermented beverage could be called beer or ale but the proper term is gruit. It was a lot of work to find out that hops is absolutely the best bittering agent to counteract the sweetness of the malt, but hops are not the only one.

    Are you an attorney for the Rheinheitsgebot? I don't think that is really in the interest of beer purity, but a protestant reaction to the power of the Catholic Church, an economic attack on small brewers, who bittered their brew with a variety of herbs, some thought to be hallucinogenic. Enough 17th Century politics and religion! -- enjoy a home brew. Skoal!

    NO yeast please, but water naturally. The fermentation process comes from the malted barley and yeast is not in this pure beer. If you can find it in your country, give it a try. Windhoek Light and there is also Windhoek Lager. Made in Namibia, Africa.

    Thanks -- I will look for Windhoek. We have the giant store Total Wine & More and they have hundreds of different beers.

    You are incorrect in assuming there is no yeast in this "pure beer." Any microorganisms present on the malted barley will not likely survive the mashing of the barley much less the boiling of the wort. Fermentation is simply the result of wild or feral strains of yeast present in the fermentation tanks or that will naturally colonize the wort over time. There are bacterial strains that will make good beer in combination with the proper yeast (try a Belgian Lambic); however, anything that is fermented without yeast is not beer at all and it will taste nothing like beer.

    Fermented without yeast? Wie kann das passiert?

    I have to take objection to your statement that "Science may not have made a... great cheep(sic) beer..." After having spent four years in Germany where I could purchase a variety of GREAT beers for $14-20 per case of 20 500ml bottles I was rather disappointed to return to the U.S. only to find that a 6-pack of comparable quality beer sold for up to $16!

    I quickly gave up buying beer and learned to make my own!

    Oh, I am so confused. In my earlier married years when I tended bar part-time to supplement my meager E-5 (USN) pay I was instructed to pout draft beer with 3/4 to 1" of foam to bring out the "real beer flavor". I soon came to suspect the foam was actually to bring out a couple of dozen extra glasses of beer from every keg. I have had draft beer foamy and non-foamy and I honestly can't tell the difference. I suspect that some of the discussion might be in the realm of martinis "stirred, not shaken", to keep from "bruising" the gin. To be honest, the darker beers that I have grown to prefer don't have as much foam, and that suits me just fine. BTW, Hank, I alwangszue [int.ys enjoy reading your articles.

    I agree with you about being skeptical of the folk wisdom of beer but psychology does play some part; if people think a certain foam is optimal, give it to them. It may be a few extra glasses but that revenue would quickly be wiped out if people thought the beer was bad because it was not optimal (if, for example, people liked no foam and thought a foam meant a dirty glass or whatever).

    The first beer I ever remember liking was in my mid-30s - a Murphy's Stout, which is nothing at all like the average commercial beer, foam-wise.  I loved the taste, but it made me feel a little queasy.  Maybe my tongue and my brain are 'elite' beer but my stomach is Pabst Blue Ribbon. :)

    Thanks for the kind words.
    Yeah, PBR is a fall-back beer for me, as well as Olympia, which I can no longer get here in eastern MO. We fortunately have several craft breweries in the area that provide an ample supply of great beers, but at a premium price. SO, I have a list of "every day' and "special occasion" beers. CONFESSION: I love beer.......foam or no foam.
    (Sure wish there was an "edit" option...I would correct my boo-boo from the last post)

    I had a glass of Heady Topper beer at the Alchemist Pub outside of Stowe, Vermont today. Even the burps tasted good! This is not your typical 2% American beer; it's four times more concentrated.
    Great writing and really enjoyed it until the very end where you have an image of a bottle of Budweiser. My favorite story about Bud was reported in Der Spiegel-- during the World Cup no one was drinking American Budweiser, and one American reporter talked a Czech into sipping some for free during an interview. The Czech's polite comment was "it lacks the taste of beer."

    Who says beer should only be made with hops and malted barley? Apart from forgetting the yeast and water-- and even the German Purity Law (Rheinheitsgebot) of 1516 calls for 3 ingredients.

    The Czech's polite comment was "it lacks the taste of beer."
    I guess you have been there so you know there beer is okay in a globalized world but nothing special.  And the food is horrid.  Plus, Eastern Europeans never have anything good to say about anything, it is what makes them so fun.  Here is Hungarian canoer Attila Vajda complaining about British food during the Olympics: "For me the meals in the UK are quite monotonous, so I wanted to eat something which is at least close to Hungarian dishes. And the closest thing was bread and butter."
    Hank, I've been to Germany 5 times but never to Czech Republic. What little I've read about Czech food is scary-- fatty meat with fat, and bread, and maybe noodles too. That is very very funny, the bread and butter comment! So hard to find British restaurants here in Southern California ... :)

    But back to Budweiser--- please tell me you can taste the enormous difference between a BudMillerCoors and any of our fine America craft beers, or a Czech pils, like the original Pilsner Urquell (German for original Pils).

    Starting off with Murphy's, you started off right :)

    My mistake-- you wrote that Murphy's was the first you really liked-- not the first beer you had--- nonetheless Murphy's Irish Stout, a wonderful first beer to really like. :)

    I can taste the difference but I don't know that I can appreciate one that much more than the other, other than knowing I really like stouts.  I just don't drink enough for it to matter.  Like I said, I have had a 4-pack of Bourbon County stouts aging since 2008 but it is mostly academic - will I appreciate it?  Probably not, that is why I will have real beer people over.  I've had pilsners in Plzeň and they were okay.  I can't fathom why people complain about American beer.  If you go to the actual Oktoberfest in Munich the beer is going to be mostly mass market stuff too. It ain't like Heineken is better than Bud just because it is from Europe.

    The Bud in the pic was used because it's what I had that I knew would make a head, not because it was any good.  I will buy anything in a red, white and blue bottle.
    Stouts and porters are my very favorite. Put on your short list Fuller's London Porter. That's the best porter I have tasted. Stouts-- so many-- Sierra Nevada makes a nice one, but way overhopped, like most American craft beer. Murphy's, Guinness, Sam Smith, all good.

    Not agree with you about waiting 5 years for the Bourbon Cty stouts-- not sure that beer improves from aging past several months--

    We can disagree I guess about mass market beers-- here in USA I think they are horrible, but in Germany, wonderful-- a Beck's or a St. Pauli Girl or any of the 7 or so Oktoberfest biers are so much better than our BudMillerCoors.

    Heinekin! We agree about Heinekin. Yes it is not better, and certainly not because it is from Europe. Switch to Beck's for a tasty lager. Or St. Pauli Girl. Or go for a Pilsner Urquell.

    Look for the Polish stouts ... some interesting things from there-- Zybweic (?)

    Not agree with you about waiting 5 years for the Bourbon Cty stouts-- not sure that beer improves from aging past several months--
    No idea, but they claim it does, that is why I bought it.
    It should. Alcohol and hops are preservatives, which is why 'export' beers tend to have higher ABV and bitterness - they need to survive the journey. Around 8-10% ABV the shelf life of beer increases dramatically due to the alcohol level, and what changes do occur in the beer tend to be neutral to good, rather than bad.

    That's not to say that any beer above 10% ABV can be aged - the flavor of hops (not the bitterness) degrades over a period of several months, so hoppy big beers like double IPA should be enjoyed soon after purchase.

    Hop compounds are also broken down by UV light, which causes the classic 'skunkiness' of old beer, keeping all beer in the dark will prevent this. This can be a problem with top-shelf beer if it's been on that shelf for 6 months - avoid dusty bottles!

    This has been in a fridge in my garage in one of those vegetable drawers or whatever down at the bottom.  So it has been controlled temperature and light. When I last read it, it said something like 14% ABV.  So it may be good - or even great - since I seem to have Forrest Gump'ed my way into storing it properly.
    ...the only ingredients that could be used in the production of beer were water, barley and hops. NOT 3 ingredients! The law also set the price of beer at 1-2 Pfennig per Maß. The Reinheitsgebot is no longer part of German law: it has been replaced by the Provisional German Beer Law, [2] which allows constituent components prohibited in the Reinheitsgebot, such as yeast, wheat malt and cane sugar, but which no longer allows unmalted barley.

    Anyway, I was just responding to Hank's statement that science may not have produced a great light beer. Windhoek Light is that great REAL light beer in my humble opinion. Maybe my tongue and taste buds are an attorney for the Reinheidsgebot. No religion, just beer drinking pleasure.

    Largest American-owned brewing company is Boston Brewery (Sam Adams).

    Can you taste the difference between a Sam Adams Boston Lager, and a BudMillerCoors? Let them warm to at least 48 F and sip, as you would a cabernet.

    We need to find a different phrase than "mass-marketed" as Jim Koch (Boston Brewery) ships his excellent suds all over. Or most of it.

    Heineken, not Heinekin. Es tut mir leid, eine Fehler zu machen. Meine Erste heute, aber nicht mein Letze.

    Nice article. In Finland the local beer is pilsner. Unfortunately, the beer either does not have any of the proteins that allow the beer to maintain the foam, enough of the bubbles in the first place or the glasses or taps are always really dirty creating nucleation sites on the glasses. Maybe they should change the glasses as their are probably better glasses for pilsner vs. stout or lagers. The science of beer foam is a hot topic that I commented briefly in my blog.