A team of Australian engineers has developed a technique to produce full-strength, full-flavour espresso at 22°C – and saving 75 per cent of the energy required of a traditionally brewed shot.
Bulletproof coffee. Nitro cold brew. Ready-to-drink ranges. The daily cup of joe has a history of hundreds of years, but coffee connoisseurs are always eyeing the next trend.
Given Australia’s international reputation as an international java hotspot, it might come as no surprise that the newest innovation in the buzzy world of caffeine hails from the eastern suburbs of Sydney.
But the innovation dubbed “ultrasonic espresso” is not the work of a carefully trained coterie of baristas. This brew is the work of a team of University of New South Wales chemical engineers.
Full body, low energy
Led by Dr Francis Trujillo, the UNSW team’s method for brewing espresso uses room temperature water and an ordinary filter basket, cutting energy use by up to 75 per cent.
A test panel of 100 coffee drinkers rated the resulting beverage as indistinguishable from espresso brewed in the traditional manner, using high pressure and hot water.
“It’s a different process, but you get the same richness and concentration of a normal espresso in under three minutes,” said 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 per cent.”
Trujillo’s innovation was to use high-frequency ultrasonic sound waves to extract a flavoursome, full-bodied coffee within minutes. The research, published in the Journal of Food Engineering, builds on previous efforts by the team to extract cold brew coffee using ultrasonic waves, accelerating the process from 24 hours to three minutes.
Cold brew, however, has a mellower flavour profile than espresso, and extracting the higher-strength, richer tasting drink familiar to cafés across Australia required refining the ultrasonic process.
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Acoustic cavitation
Trujillo’s team’s brewing technique uses ultrasound to replace heat with mechanical energy. A small metal transducer pressed against the side of the coffee filter produces high-frequency waves that vibrate through both the grounds and the water.
“This creates a phenomenon known as acoustic cavitation. Tiny bubbles form and collapse in the liquid,” Trujillo explained in The Conversation.
“When these bubbles collapse near coffee particles, they produce microscopic jets and forces that act a little like scrubbing brushes. They pit and fracture the surface of the coffee grounds, helping flavour compounds, oils and caffeine move into the water much faster than they normally would at room temperature.”
The team developed a resonant horn design that coupled with the transducer to create multiple cavitation zones with greater generator stability. By refining the horn’s geometry, it was able to improve the filter basket’s dominant resonance mode, enhancing the effectiveness of the ultrasonic waves.
“The cylindrical horn tip excites a single, in-phase resonance mode of the coffee basket,” the team reported in its research.
“This results in coherent mechanical motion and a stable impedance condition, enabling the generator to operate near its optimal matching point with clearly defined standing-wave behaviour.”
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Coffee at scale
Ultrasound has been demonstrated to have other culinary uses beyond brewing coffee, including preserving, extracting and processing food. World champion baristas have also applied ultrasound to their traditionally brewed espresso to improve the flavour after it has been extracted.
And although Trujillo’s ultrasonic espresso could be brewed by home aficionados or local cafes, he foresees its greatest benefit being for companies that produce coffee at industrial scale – and would therefore benefit most from the energy savings the process delivers.
This concentrated, quick-to-produce, espresso-strength coffee could be shipped as a concentrate that could later be diluted for cold brew or milk-based beverages, or used for ready-to-drink products.
“As someone from Colombia, I like to think coffee is in my blood – and I’m proud to come from a country known for producing some of the best coffee beans in the world,” Trujillo wrote.
“Those results show espresso may not need to begin with hot water after all.”
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