Their research, published in the Journal of Food Engineering, included blind taste-testing experiments which showed that their ultrasonic room-temperature version of espresso was undistinguishable from coffee shots brewed in the traditional way.

“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,” says Dr 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.”

Dr Trujillo had previously developed the patented ultrasound system to create cold-brew coffee, which usually takes 12 to 24 hours to produce, in as little as three minutes.

However, cold-brew coffee has a distinctively different flavour to espresso – often described as being much more diluted, smooth and mellow – while also containing around one-fifth the caffeine concentration.

The UNSW team continued their work to adjust the ultrasound system to create an espresso-strength shot without the need for hot water.

The process transformed a traditional filter basket into an ultrasonic reactor to brew the grounded coffee beans. The basket generates high-frequency sound waves that help extract flavour, aroma and body from the coffee grounds.

At the heart of the system is a transducer - a small metal device that generates ultrasound while pressing against the side of the coffee basket holding the ground coffee. The ultrasound causes the basket vibrate rapidly, transmitting vibrations through both the coffee grounds and the water.

The ultrasound creates a phenomenon called acoustic cavitation, which is a rapid formation and collapse of microscopic bubbles in the liquid. When these tiny bubbles collapse near the coffee particles, they act like microscopic scrubbing brushes or jets of liquid, pitting and fracturing the coffee grounds and accelerating the bewing process.

This helps break open the surface of the coffee grounds and allows flavour compounds, oils, and caffeine to move into the water much faster than they normally would at such low temperatures.

The result is a concentrated, flavourful shot of coffee comparable to espresso made with traditional machines, but produced using room-temperature water and much less energy.