Researchers at UNSW Sydney have developed a new coffee brewing process that could reduce energy consumption in beverage manufacturing by up to 75%, using ultrasonic sound waves to produce espresso-strength coffee with room-temperature water.
In a media release, the university said the technology, developed by researchers from its School of Chemical Engineering, creates what it calls an “ultrasonic espresso” by using high-frequency sound waves to extract flavour, aroma and caffeine from coffee grounds without the need for heated water.
According to the research, published in the Journal of Food Engineering, the process can produce an espresso-strength coffee in less than three minutes while significantly lowering energy requirements compared with conventional espresso brewing methods.
“We call it an ultrasonic espresso. It’s a different process, but you get the same richness and concentration of a normal espresso in under three minutes,” said Dr Francisco Trujillo.
“Traditionally, espresso is by forcing hot water through coffee under pressure. But with ultrasound we can use room-temperature water instead, reducing energy consumption by up to 75%.
“And when we gave our ultrasonic espresso to 100 regular coffee drinkers in a randomised test, they could not tell it apart from a normal espresso.”
The researchers adapted a traditional coffee filter basket into what they described as an ultrasonic reactor. A transducer attached to the basket generates ultrasound waves, creating a phenomenon known as acoustic cavitation, in which microscopic bubbles rapidly form and collapse in the liquid.
UNSW said this process helps break down the surface of coffee grounds, allowing flavour compounds, oils and caffeine to be extracted more quickly, even at low temperatures.
The team said it spent considerable time refining brewing parameters, including brew ratio, grind size and ultrasound application time.
“We have been working on a range of parameters to discover how to make the perfect ultrasonic espresso,” Dr Trujillo said.
“The most important was the brew ratio – that is how much water is used per gram of coffee – because this helps ensure the final drink is concentrated and not too diluted.
“We found that by grinding finer we could extract the flavour more rapidly.”
Researchers also conducted a blind sensory evaluation involving about 100 regular coffee drinkers. Participants sampled traditional espresso, ultrasound-brewed espresso, traditional filter coffee and ultrasound-brewed filter coffee without knowing which version they were tasting.
UNSW reported that participants found no significant differences between traditional and ultrasound-brewed espresso across measures including aroma, flavour, bitterness and overall liking. For filter coffee, the ultrasound-brewed version received higher overall ratings and was considered less bitter.
“These findings showed that using ultrasound did not harm taste, and in some cases even improved it, despite brewing at room temperature and without the heat normally associated with coffee making,” Dr Trujillo said.
While the technology could potentially be incorporated into consumer coffee machines, the researchers said its greatest manufacturing opportunity may lie in large-scale production of ready-to-drink coffee products.
“There are companies that make coffee products on an industrial scale and we are confident this ultrasound system can be scaled up to meet their needs, delivering real benefits in terms of reduced processing times and energy use,” Dr Trujillo said.
“The 75% energy saving is particularly beneficial at that scale and we are also able to produce the coffee very quickly.
“Because the process produces a concentrated, espresso-strength coffee, it can be used directly to manufacture ready-to-drink products, or shipped as a concentrate and later diluted into a range of drinks, including cold brew and milk-based coffee drinks.”
