Coffee beans sing distinct tune.
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, Preston Wilson of the University of
Texas at Austin reported in the June Journal of the Acoustical Society
of America. Java roasters know to listen for some sounds, called
"first crack" and "second crack," but until now no
one had analyzed the noises, Wilson says. He roasted a small batch of
green coffee beans in an electrically heated drum roaster and recorded
the crackling sounds. 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 730 seconds, which snap rapidly like Rice Krispies in
milk. Measuring the beans' sounds is a step toward making an
automatic acoustic roaster, Wilson suggests.