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Headline: The end of the kettle? Scientists brew espresso using room-temperature water and sound waves
Caption: Researchers have found a way to make espresso-strength coffee using room-temperature water and ultrasonic sound waves - cutting energy use by up to 75%. Scientists at UNSW Sydney say the breakthrough could transform how coffee is produced, particularly for large-scale manufacturers of ready-to-drink beverages. The new brewing method uses high-frequency sound waves to extract flavour, aroma and caffeine from coffee grounds without the need for boiling water. Researchers claim the resulting drink delivers the same rich flavour, body and caffeine hit as a traditional espresso and can be produced in under three minutes. The team, led by Dr Francisco Trujillo from UNSW's School of Chemical Engineering, tested the coffee on around 100 regular coffee drinkers in blind taste trials. Participants were unable to distinguish between the ultrasonic version and a conventionally brewed espresso. Dr Trujillo said: “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. “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 technology builds on earlier work by Dr Trujillo, who developed a patented ultrasound system capable of producing cold-brew coffee in minutes rather than the usual 12 to 24 hours. But while cold brew is known for its smoother, milder flavour and lower caffeine content, the researchers wanted to create something closer to a traditional espresso shot. To achieve this, they modified a standard filter basket into what they describe as an ultrasonic reactor. A small metal device known as a transducer presses against the side of the basket and generates ultrasound waves, causing rapid vibrations throughout the coffee grounds and water. These vibrations create a process known as acoustic cavitation, where microscopic bubbles form and collapse at high speed. The collapsing bubbles effectively blast apart the coffee particles, helping flavour compounds, oils and caffeine move into the water much more quickly than would normally be possible at room temperature. The result is a concentrated coffee shot comparable to one produced by a standard espresso machine but requiring far less energy. Dr Trujillo said: “We have been working on a range of parameters to discover how to make the perfect ultrasonic espresso. “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. “Another important factor is how finely the coffee beans are ground. We found that by grinding finer we could extract the flavour more rapidly. “We also experimented with how long the sound waves were applied, as this can affect both the concentration and flavour of the coffee. What we found is that between two-and-a-half and three minutes is a sweet spot for producing a balanced cup.” For the taste tests, researchers prepared four drinks: traditional espresso, ultrasound-brewed espresso, traditional filter coffee and ultrasound-brewed filter coffee. All were freshly made, cooled to the same temperature and served in identical coded cups in random order. Participants rated each coffee for aroma, flavour, bitterness and overall enjoyment using a nine-point scale. Researchers found there were no significant differences between the traditional and ultrasound espresso shots across any category. Most participants could not tell them apart and showed no clear preference for either. The ultrasound-brewed filter coffee performed even better, with participants rating it more favourably overall and finding its bitterness more pleasant. Dr Trujillo said: “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.” The researchers believe the technology could eventually be adapted into home coffee machines. However, they say its biggest potential lies in commercial coffee production, where reduced energy consumption and faster processing could deliver significant savings. Dr Trujillo said: “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. “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.” The findings have been published in the Journal of Food Engineering.
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PersonInImage: Dr Francisco Trujillo