Brewing espresso at room-temperature
TECHNOLOGY
A team of Australian chemical engineers at the University of NSW has developed a full-strength, full-flavour espresso at just 22°C, saving 75% of the energy required for a traditionally brewed coffee.
The team, led by senior lecturer Dr Francis Trujillo, uses room temperature water and an ordinary filter basket to brew the “ultrasonic espresso”, as it’s being dubbed.
A test panel of 100 coffee drinkers rated it 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,” says Trujillo. “Traditionally, espresso is made by forcing hot water through coffee under pressure. But with ultrasound we can use room-temperature water instead.”
The process uses high-frequency ultrasonic sound waves to extract a flavoursome, full-bodied coffee within minutes and 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.
Trujillo’s technique replaces 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 explains. “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 to move into the water much faster than they normally would at room temperature.”
Ultrasound has been demonstrated to have other culinary uses, including preserving, extracting and processing food. World champion baristas have also applied ultrasound to their traditionally brewed espresso to improve the flavour after it’s been extracted.
And although ultrasonic espresso could be brewed by home aficionados or local cafes, Trujillo suggests those who produce coffee at scale would benefit the 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 says. “Those results show espresso may not need to begin with hot water after all.”
TOP Francis Trujillo
PHOTO UNSW/Richard Freeman
ABOVE How the ultrasonic espresso system works
PHOTO Francisco Trujillo/UNSW
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