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Coffee beans sing distinct tune

Crackling sounds could be key to automated acoustic roasters

10:00am, May 26, 2014

CUP OF JOE  As they roast, coffee beans emit a chorus of crackles that begins with low, loud noises and ends with quick snaps that sound like Rice Krispies in milk.  

Listen to the audio

The snap-crackle-pop of coffee beans could tell automatic roasters when to turn down the heat.

Hot beans sing a distinct ditty that reveals their stage in the roasting process, mechanical engineer Preston Wilson of the University of Texas at Austin reports in the June Journal of the Acoustical Society of America.

Java roasters know to listen for some basic sounds, commonly called “first crack” and “second crack,” but until now no one had measured and analyzed these noises, Wilson says. He roasted a small batch of green coffee beans — an espresso blend — in an electrically heated drum roaster and recorded the crackling sounds as the beans got toasty.

The first crack noises, which sound like popping corn, ring out between 400 and 600 seconds after roasting begins. Those crackles are louder, deeper and less frequent than the second chorus of cracks at 620 to

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