By Katherine Shonesy
POTTSTOWN PA – What makes a product of Pottstown’s Sly Fox Brewery taste different than a beer from, say, Yards Brewing in Philadelphia or Victory Brewing in Downingtown? For that matter, why is the cup of coffee sold at Starbucks more or less palatable than one poured at McDonald’s?
It’s the magic of chemistry that matters in both cases, according to Dr. Tracy Hamilton, a theoretical chemist and associate professor at the University of Alabama in Birmingham.
Hamilton typically conducts his research in quantum mechanics, which deals with the behavior of matter and energy. Years ago, though, he also discovered a passion for zymurgy, the science of fermentation. And when a friend of Hamilton’s began roasting his own coffee beans, that too drew his attention. Now he travels the country on behalf of the American Chemical Society, lecturing about how the chemical make-up of beers and coffees affect the way they taste.
“It’s a really popular topic,” Hamilton said; scientists “love talking about beer and, of course, drinking it.” Even career chemists learn something from his talks, he proudly added … such as the fact that the flavor and aromatic compounds in beers and coffees are also present in other foods.
Flavors in beer come from a surprising number of sources. One is the variety of sugar-type compounds in the beverage, which give brews their sweetness. Other than sugars, much of a particular brew’s complexity comes from the hops used in its production. Essential oils in hops “contribute a lot of flavors like citrus, grapefruit and orange,” Hamilton said. “They’re what you smell.”
Compounds such as geraniol and citral are extremely common in beer, giving it a geranium-like or citrusy smell, respectively.
A few flavor and aroma compounds can be less savory. If a beer does not ferment long enough or correctly, it may taste like Granny Smith apples, thanks to acetaldehyde. This compound, produced as an intermediate step in fermentation, is not pleasant, Hamilton noted. Another undesirable compound is 2-transnonenal, which tastes like damp paper.
Some styles of beer do not have much hop flavor at all, and derive many of their flavors from the brewing yeast. “In ales, there are a lot of ester compounds that come across as pretty fruity,” Hamilton said. “It’s all about the balance. You don’t want it to be overwhelming.”
As for coffees, much of their flavors come from pyrazines, small aromatic compounds that form when the brew is freshest. “That’s one reason coffee is so much better when it’s fresh,” Hamilton said.
Other aspects of coffee’s flavors come from sugars that are broken down by roasting. The Maillard reaction, the same heat-driven chemical event that browns steaks and toasts bread crusts, roasts beans to yield compounds that lend a special – or not so special, depending on your nostrils and taste buds – sip-ability to each blend.
So which would Hamilton prefer, a cold brew or a hot one? Depends on the time of day. No matter what he’s drinking or when, however, he said the uniformity of the beverage is important. The most desirable trait in coffee or beer, Hamilton claimed, is that “every sip is the same.”
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