Studying at the Bar

When I was touring the state gathering material for
Michigan Breweries, one of the livelier debates involved brewing: was it an art, or was it a science? After sampling the brewers' wares, I concluded there was no clear answer, but told them I'd be happy to keep investigating.

From the science side of the debate comes Mark Denny, who earned a doctorate in physics at Edinburgh University and now makes his home in Canada. He calls himself "a physicist by training and a homebrewer by inclination." Both come together in his book
Froth! The Science of Beer which, he ways, "unites brewing with accessible physics." Quite successfully, I might add.

Before plunging into the science, Denny puts it into historical perspective. Science didn't enter brewing until about 150 years ago, before which time most beer was brown in color and prone to go bad. It was a far cry from today's attractive-looking, consistent, and hygenic beer. That said, scientific advances don't always mean better beer. Besides the obvious culprits like artificial carbonation, Denny cites more subtle ones. For example, differences in the local water and temperamental strains of yeast, which account for subtle differences in taste, are gone: brewery executives sacrificed them in the name of consistency.

The science itself–complete with equations and graphs–begins with a discussion of the population dynamics of yeast. Denny explains why those sachets you find in homebrew stores contain far too few yeasts for an efficient fermentation. He recommends re-using yeast from a previous batch. That's a homebrewing tip you won't find in "the book" but, being a good scientist, he's tried and tested them all. But back to the physics. Denny explains what goes on behind the scenes after the yeast is pitched. During the lag phase, when nothing seems to be happening, the yeasts are gobbling up oxygen and reproducing at an incredible rate. Once the wort turns foamy, the population nosedives as the yeasts lay down their lives for a worthy cause: turning sugar into alcohol.

The next physics lesson involves brewing thermodynamics. Homebrewers are keenly aware of the importance of raising wort to the proper temperature and keeping it there. Denny constructs a mathematical model that accounts for the major influences on wort temperature, like the size of the vessel and the power of the heating element. As in the case of yeast population, his thermodynamic model is consistent with homebrewing, down to the amount of wort–11 percent–that you can expect to lose to evaporation. There's a larger lesson here: constructing a model, then refining it to conform to reflect real-life experience, is what good scientists do.

Like many beer lovers, Denny is fascinated with bubbles, and goes into great detail about how they are formed, how many you'll find in a batch of homebrew, and why some of them appear to be falling (yes, they really are). He explains why bubbles move more slowly in beer than they do in Champagne, how the head on a glass of beer forms and decays, and why Belgian beers are likely to contain–get ready for this–
anti-bubbles. And he tells you why the ritual of pouring out a pint, and the importance of choosing proper glassware, are both solidly grounded in physics.

Finally, Denny explores the science behind getting beer from the brewery to you. At the front end there's distribution, with its multiple interacting variables. Because optimal distribution means a big payoff, this subject has have kept applied mathematicians busy for years. At the other end are the complex mechanics involved in lifting a beer glass. It took millions of years to evolve the machine called the human hand–and we haven't even gotten to the complex feedback mechanism between the hand and brain which, you've probably figured out, can get overwhelmed by alcohol.

Froth! isn't all hard science. Denny takes note of other influences on beer, such as how high excise taxes forced brewers to hop their beer and why pale ale became the drink of Britain's middle class. He offers the appealing argument that humans switched from a hunter-gatherer lifestyle to agriculture because they'd grown fond of beer. And he's thrown in some interesting trivia. For instance, in Shakespeare's time, the first runnings of beer checked in at 13 percent ABV; and even small beer–the kind Jake the Butcher wanted to make a felony to drink–was as potent as today's national brews.

The author serves up a generous pour of science, but it goes down easily. If you're intimidated by equations with Greek letters and integral signs, fear not: he explains it in understandable English, lightened by plenty of humor. He even rewards you with a beer (okay, a photograph of one) for plowing through all of that math.
Froth! earns a solid "A" for bringing science, brewing, and good writing together.