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Study: Acoustics of a coffee bean

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Posted January 7, 2015

Coffee is one of the most widely consumed beverages worldwide. Coffee consumption is highly prevalent with more than half of all Americans over 18 drinking on average amounting to 300mg of caffeine per person per day – the equivalent to between two and four cups of coffee according to a 2012 report from the US Food and Drug Administration (FDA). Moreover, the study reports that coffee consumption has increased one percent each year since the 1980s, increasing to two percent in recent years.

Picture: Roasted coffee beans. Image credit: MarkSweep via Wikimedia Commons/Public domain

Picture: Roasted coffee beans. Image credit: MarkSweep via Wikimedia Commons/Public domain

These numbers are not surprising because there are so many reasons why we like and why we need to drink coffee. Scientists have already validated coffee’s health benefits  –  coffee reduces the risk of death from liver cirrhosis by 66%, reduces risk of developing liver cancer, protects against periodontal disease, coffee may help lower the risk of developing diabetes, non-alcoholic fatty liver disease, and possibly has many other benefits.

But have you heard anything about specific sound of coffee beans?

Acoustic researcher Preston Wilson from the University of Texas normally spends his time studying underwater sounds. But, like many of us, the author relies on coffee to keep him energized. He’s also quite a coffee connoisseur, as he roasts beans on his own. Lately he noticed that the sounds those beans make while roasting give away in what stage of the cooking process they are.

Wilson explained that there are a number of ways human roasters and automated roasting machines know when to stop the roasting process – they can judge by time, color, aroma, temperature, even the gas content in the roasting chamber. But he found a simpler technique. He said that we need just to listen to the sounds of the beans, which are remarkably consistent from one batch to another. At around 200 degrees Celsius, beans emit a “first crack,” releasing the expanding gas and steam that have been building up inside them. At around 230 degrees Celsius they emit a “second crack,” which is softer and more rapid than the first crack, and after which the beans start to burn.

The author in his study measured, analyzed classified all sounds during roasting process, including the sounds of first crack and second crack, and the background noise produced by the rotating drum and by the circulating fan. Three acoustical characteristics of the process were found that could be used to form an automated acoustical roast monitoring technique: first crack is louder than second crack (by 15% in peak acoustic pressure), first crack is significantly lower in frequency than second crack (by a factor of nearly 19), and second crack events proceed at a higher rate (by a factor of about 5) than first crack events.

Scientist believes that sensitivity to bean cracks could be programmed into a new generation of roasting machines, which would turn off when the beans sound exactly right. If engineers could design a device that listens to and evaluates roasting beans’ chatter (and it is very likely that engineers could do that), people might one day be able to wake up and hear their coffee approaching a perfect state.

Sourcesscitation.aip.org, caffesociety.co.uk, censeoav.comfda.gov, Science Dailyjoponline.orgsciencecodex.com

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