The Biology, Chemistry and Physics of Coffee

After many years in grad school, Pauline Fujita of Litmus has had at least as much coffee as science, yet like most of us, she knew very little of the brewed beverage. So, Pauline decided to delve a little into the science of coffee.

Take, for instance, the science behind the aroma of coffee:

Most of the aroma we associate with coffee is created during the roasting process. Longer roasting times mean coffee that is more bitter and less acidic and darker in color (Fortin 1999). Green, or un-roasted coffee contains about 300 volatile organic compounds (Bonnländer et al. 2005 pp. 198) whereas over 1000 such compounds have been found in roasted coffee. The green bell pepper-like “aroma” of green coffee can be attributed primarily to the compound isobutylmethoxypyrazine. In contrast, the aroma of roasted coffee is thought to result from a combination of about 25 volatile organic compounds, the “aroma compounds”, found at a total concentration of only 1g/kg of coffee and ranging in individual concentration from the lower part per million range down to as little as parts per trillion.

So where do all these extra compounds come from? During the roasting process many different chemical reactions occur, the most important of which can be classified as one of two types of reactions. The first, Maillard or “browning” reactions, produce aroma compounds as well as colored compounds (melanoidins), and the second, caramelization reactions, involve the chemical reduction of sugar compounds, the same tasty process that, you guessed it, makes caramel.

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