Listen to Your Coffee Beans—It’ll Perfect Your Roasting Skills

Coffee beans make different noises depending on how toasted they are

Photo: 237/Adam Gault/Ocean/Corbis

Acoustic researcher Preston Wilson normally spends his time studying underwater sounds. But, like many of us, Wilson often relies on coffee to keep him energized. He's enough of a coffee connoisseur, too, that he roasts his own beans. And he noticed that the sounds those beans make while roasting give away where they are in the cooking process. These clues, he thinks, could be harnessed to perfectly time a light, medium or dark roast's preparation.  

Think, as an analogy, about popcorn. Listening is a big part of getting popped popcorn right. As the flurry of pops begins to subside, experienced poppers know to stop the microwave or risk burnt kernels. Wilson noticed that, like popcorn, his roasting coffee beans emitted different sounds depending on how far along they were in the roasting process.

To satisfy his own curiosity, he decided to quantify those sounds, including what's known among coffee roasters as the "first crack" and "second crack." He measured when those cracks occurred and classified them according to different acoustic amplitudes. "The sound of the first crack is similar to popcorn popping, while the second crack is more akin to the sound of the breakfast cereal Rice Krispies," he said in a statement. 

Creating a machine that monitors the rate and amplitude of cracks, he thinks, could lead to an optimized coffee roasting experience. For companies, this might mean less energy consumption during the roasting process. And for individuals like Wilson, this could mean fewer bags of expensive beans lost to botched roasting sessions. 

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