Scientific Sleuthing and Bad Beers

Highlights from my conversation with Jon Roll, a UW professor of Bacteriology.  Roll teaches a brewing class for undergraduates, using professional equipment donated by MillerCoors.

I wrote a news story for my Science Journalism course about a beer tasting Roll led as part of the Wisconsin Science Festival, with some of the information from this interview. But, Roll had more interesting things to say about the science of brewing and the need for an conscious tasting than I could possibly fit into my 500 word story.

“We tend to be somewhat oblivious,” Roll said about the sense of taste.  He explained that learning about taste is a process of educating your tongue and educating your senses.

For him, the aha moment came when drinking beer with Roy Desrochers, a professional beer taster. Roll said he became much more aware of things he had not been aware of before, as Desrochers pointed things out.  “He was fascinated with the progression of flavors,” Roll explained, “From sweet to malt to bitter that slid down the back of your throat. The whole thing took like a minute from when you took the sip.”

In Roll’s class, his students have to learn to taste the subtleties of beer as well. There are common problems in the complex brewing process that can create a variety of “off-flavors” in the beer. To go back in the process a fix the mistake, brewers have to know what chemical compound is creating the off-flavor.  You can buy a kit of common off-flavors to practice with. They train themselves to identify these compounds by drinking beer purposely spiked with a common chemical culprit, so they form conscious associations between off-flavors and specific chemicals. Tastes and smells are hard to accurately convey to someone else, one might think “woodchips” and someone else might think “file cabinet”, in an example Roll gave.  By having all the tasters try the same chemicals in beer, they can learn to associate the taste with the compound, even if they describe the sense of that chemical differently.

In the brewing classes that Roll teaches at UW, his students use scientific sleuthing to track down how these specific chemicals were produced. Figuring out where that specific chemical came from requires tracing back through genetic regulation and biochemistry. Maybe the temperature was off slightly, causing certain enzymes to catalyze and unwanted breakdown. With their sense of taste attuned, the students can track the problem. This way, they understand how to alter the brewing to prevent the off-flavors. They can use the same techniques to replace specific successful flavors as well. At this point, Roll explained, human taste is still the most sensitive instrument we have for detecting trace amounts of certain things in our food and drink.

Although he’s not a tasting professional, Roll enjoys teaching about the science of beer. “Beer is all over in our society, history, heritage. The brewing industry is big in Wisconsin.  People enjoy learning about it.”   He also explained that beer is a great place to start talking about science because everyone is excited about beer and “there is so much science involved. Engineering, chemistry, gene regulation, put together in something very tangible.”

A new kind of Soda fountain…

Scientists love explosions.  They love using explosions, like the popular Mentos and Coke reaction, to get people excited about science. Add Mentos candies to a bottle of Diet Coke, and it will erupt in a fountain of bubbles, spraying 5-10ft high.

After the fountain subsides, students brainstorm: how and why did this reaction happen? The simple answer is that the rough surface of the candies provides lots of little growth sites for bubbles. The truth, like many things in science, is a bit more nuanced. In June, 2008, a physics professor from Appalachian State College and her students published a paper demonstrating all the factors that effect the reaction. Tonya Coffey’s class tested a variety of hypotheses by repeating the reaction with different kinds of soda, different candies, and other substances that have similar characteristics to the Mentos, like the rough surface of rock salt or sand.

They tested the rough surface hypothesis by comparing Wintergreen Lifesavers to Mentos.  Both candies, the rock salt, and even dish soap, caused bubbling eruptions. Anything dropped into the soda can break the fragile bonds between water molecules, allowing carbon dioxide bubbles to grow. But not all of the eruptions were the same size.  Under a microscope, the surface of the Lifesavers appears 5 times as rough as either the mint or fruit Mentos, which are very similar.  However, the eruption with the Lifesaver is half the size of the average mint or fruit Mentos eruption.

The difference they discovered is that Mentos are very dense, and sink to the bottom of the soda bottle 33% faster than the Lifesavers. The bubbles created at the bottom now have to travel all the way back to the top of the bottle to escape. The bubbles create a chain reaction, each one creating more as they disrupt the cohesion of the water molecules. The bubbles that travel from the bottom create more pressure, causing a more powerful the eruption. Coffey compares the Lifesaver’s reaction to a volcano slowly oozing lots of lava, instead of spraying high into the sky like the Mentos.

The second factor Coffey’s team found that plays a role in the high spray of the Diet Coke and Mentos or Fruit Mentos is the fact that the Coke is diet.  The artificial sweetener, aspartame, weakens the bonds of the water molecules in the soda. This makes it easier and faster to for the Mentos to break those bonds and start building bubbles.  A bottle of regular Coke erupts too, just not quite as high.