Is Corona For Posers?

shutterstock_6423052.jpgThis afternoon’s session sponsored by the Younger Chemists Committee about the chemistry of alcohol (the second in a series the organizers like to think of as "Insert your vice here") was standing-room only. It seems a lot of chemists are doing some experimentation outside the lab: When asked, roughly 10% of the audience said they brewed their own beer. Before going through a rather comprehensive look at chemistry of the beer-brewing process, Ferris State University professor and homebrewer Mark Thomson told the audience, “I don’t think there’s any bad commercial beer out there. There are just some I wouldn’t choose to drink, even if you choose to buy them for me.” I’m guessing one such beer might be Corona, which UNC-Chapel Hill professor Malcolm Forbes called out in his talk about skunky beer. Forbes’s specialty is photochemistry, and he’s used electron paramagnetic resonance spectroscopy to study the mechanics of how and why beer gets that sulfurous smell. I won’t go into the gritty details, but one interesting tidbit I came away with was that the “lightstruck flavor” (i.e. that skunky taste caused when UV light shines through your bottle for too long) is caused by 3-methylbut-2-ene-1-thiol. Ironically, this compound has nothing to do with what makes actual skunks stinky. Rather, it's something found in cat urine. “When you hear somebody complain, ‘The beer in this place tastes like cat piss,’ they’re not that far off,” Forbes said. Another tidbit? Why is it that everyone puts a lime in their Corona? Apparently Corona, despite its clear glass bottle, doesn’t contain any of the “advanced hop products” some companies use to slow down the radical formation that leads to a bad beer. The company’s got a good marketing scheme going on; that lime is a pretty essential flavor mask. For any doubters, Forbes recommends opening up a bottle and taking a whiff.

Author: Lisa Jarvis

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  1. This is quite fascinating chemistry. Riboflavin (vitamin B2) acts as a photosensitzer, catalyzing the formation of singlet oxygen which reacts with isohumulone, creating a radical which then abstracts a thiol group a protein, thereby producing MBT (3-methylbut-2-ene-1-thiol). For those interested there is a reaction scheme here:

    And as Harold McGee has pointed out, the same type of photochemistry also occurs in milk, butter, olive oil. That’s one reason why milk isn’t (or shouldn’t be) sold in clear glass bottles.