The physics of beer bubbles
Ever stare at a glass of beer and become tranfixed watching the bubbles? Mark Denny has . He is a physicist and a home brewer who has written a book "Froth, The Science of Beer" published this month by the Johns Hopkins University Press.
I read his chapter on the bubbles in beer the other day. I confess I had to read it twice because there is a lot of math and physics in the text. Imagine that in a book about the science of beer.
I will skip over the formula used to derive the "mean bubble radius" of the bubbles in beer. But Denny knows it .
Being a scientist , Denny sees more in beer bubbles than the average bar patron, For instance he tells us, that the generation and dissipation of bubbles in a glass of beer fall into four categories.
In the first step, the bubbles form in the glass. Next comes beading or creaming when the bubbles rise to form a head. In the third stage the big bubbles get bigger and smaller ones shrink, a process called disproportionation. Finally there is drainage, when the beer falls out of the head, leaving dry foam, or a Denny calls the dry foam " polygonal-shaped bubbles."
The next time you stare at drained glass of beer , be sure to notice the polygonal bubbles.
Ever see bubbles emerge from a spot on the side of your glass? That, Denny tells us, is a "nucleation site". This site, he explains, is caused by a dust spec, a spur in the glass or some other defect in the side of the glass that permits the dissolved CO2 to exit the liquid beer and fly upward as a bubble.
Below is his description ( with the physics in parentheses) of how to correctly pour beer from a bottle to a glass.
"Tip a clean, air-dried glass ( one with few nucleation sites to prevent excessive foam) to an angle of 45 degrees and pour the beer slowly from the bottle ( to avoid mechanical agitation and to allow time for the head to foam .)
Gradually raise the glass upright as it fills ( to avoid spilling the beer ,idiot).
Finish with a flourish by increasing the distance from bottle to glass as you pour the last of the beer ( to increase mechanical agitation and so generate more forth, so that it projects above the glass , and a little of it spills over the edge).
Do you follow?
It seems Denny tilts his glass when pouring. Others pour down the middle of the glass.
Which way do your pour?
I am trying to get an interview with Denny. I did not do well in physics in high school. So what questions should I ask him about the physics of beer?
Comments
I've always perceived differences in the feel of carbonation from force carbonated vs bottle conditioned beers. The carbonation often feels fuller, richer, like the bubbles are smaller. Is this me making stuff up? Can a beer with X units of forced carbonation and the same beer beer with the same amount of carbonation from bottle conditioning have different feels to the carbonation?
(Dustin : I will ask Denny the beer physicist this afternoon and let you know)
Posted by: Dustin Moore | May 15, 2009 7:51 AM
Hi Rob,
In the last few months, as I've been telling people about my next book, some of my more polite acquaintances seem puzzled by its very existence. (The less polite laugh their heads.) Why would anyone want to take a course in beer? Isn't college really a four-year course in beer already? In a way, it's those attitudes that were part of the reason for this book
I wrote The Short Course in Beer because it’s time to learn what much of the world already knows: beer is complex, delightful and an interesting companion to good food. There are so many people who have discovered this lately that there’s a community of beer-lovers developing that’s devoted to and knowledgeable about good beer. Perhaps it’s a coincidence, but this beer-loving community seems attached to some solid, earthy values that seem suddenly appropriate. Beer has become the drink of the energy-conscious, conservation-oriented, planet-sparing gourmet. You can raise a glass of something delicious and be on the side of the angels.
If you haven’t been paying attention, you might be surprised by all this: beer used to have a bad reputation in some places and it may have even earned that reputation once upon a time. How seriously could we take a drink associated with:
•• Drunken kegger parties,
•• lager-crazed soccer fans
•• freezing-cold tasteless liquid and
•• moronic TV commercials
But things have changed. Some of the most creative minds in the world of taste are brewing delicious beer and others are cooking food to complement it. Historic craft-beer traditions are being revived, and new ones are being created. Brewpubs are brewing their own beer and home brew enthusiasts are following suit. There are craft-beer festivals and beer tasting parties. For the competitive types, there are even competitions and medals and bragging rights. Most of all, there’s a lot of startlingly delicious, beautiful beer available for your pleasure. It’s time to get in on the fun.
When you finish this book, you will
• Know that beer is a truly complex and wonderful drink, worthy of your attention and a companion for the finest food.
• Be able to make sense of all those wonderful flavors.
• Know how beer is brewed and where its flavor comes from.
• Understand the difference between the beers that are worth your time and digestion and the ones that aren't.
• Have a few thoughts about the place of alcohol in life.
• Appreciate the intimate relationship between beer and civilization
• Know how to find and enjoy a good brew and have a laugh at the rest.
• Be able to speak knowledgeably about beer, whenever knowledgeable speaking is appropriate.
Anyway, if you'd like to see a copy, please let me know. Thanks, Lynn
Posted by: Lynn Hoffman | May 20, 2009 5:11 PM
Interesting article you have here. Now we don't have to wonder about those beer bubbles!
Posted by: David Stock | June 16, 2009 6:11 AM