Brewing espresso without heat? Now that’s sound science

PETALING JAYA: For coffee lovers, espresso has always seemed to require two essentials – hot water and pressure.

But researchers at UNSW Sydney have challenged that assumption, developing a brewing method that uses ultrasonic soundwaves and room-temperature water to produce espresso-strength coffee with the same flavour, body and caffeine kick as a conventional shot.

The findings, published in the Journal of Food Engineering, suggest the technique could reduce energy consumption by up to 75% while producing coffee that most drinkers cannot distinguish from traditionally brewed espresso.

Led by Francisco Trujillo from UNSW’s School of Chemical Engineering, the team developed what they call an “ultrasonic espresso”, using high-frequency sound waves to extract flavour compounds, oils and caffeine from coffee grounds without the need for heated water.

“It’s a different process, but you get the same richness and concentration of a normal espresso in under three minutes,” said Trujillo.

Traditional espresso machines force hot water through finely ground coffee under pressure. The UNSW system instead transforms a standard filter basket into an ultrasonic reactor.

A small device known as a transducer generates soundwaves that create microscopic bubbles in the water. As these bubbles rapidly form and collapse – a process known as acoustic cavitation – they help break down coffee particles and accelerate the extraction of flavour, aroma and caffeine.

The result is a concentrated coffee comparable to espresso, produced with room-temperature water in about 2.5 to three minutes.

To see whether consumers could taste the difference, the researchers conducted a blind tasting involving around 100 regular coffee drinkers. Participants sampled four beverages: traditional espresso, ultrasonic espresso, traditional filter coffee, and ultrasonic filter coffee.

The espresso results were striking: participants found no significant differences in aroma, flavour, bitterness or overall enjoyment between the traditional and ultrasonic versions. Most could not reliably tell them apart.

The ultrasonic filter coffee performed even better, with participants rating it more favourably overall and describing its bitterness as more pleasant.

The research builds on Trujillo’s earlier work using ultrasound to speed up cold-brew coffee production. While conventional cold brew can take between 12 and 24 hours, the team’s previous system reduced the process to just a few minutes.

While the technology could eventually find its way into home coffee machines, Trujillo believes its greatest potential lies in large-scale commercial production.

Because the process produces concentrated coffee quickly and with significantly lower energy use, it could be used to manufacture ready-to-drink beverages, coffee concentrates and milk-based coffee drinks more efficiently.

“The 75% energy saving is particularly beneficial at that scale,” said Trujillo. “We are able to produce the coffee very quickly.”

It remains to be seen if the tech eventually finds its way into cafés or factory production lines. If it does, the future of coffee may not be brewing over a flame, but riding a wave of sound.