A novel way to brew coffee without boiling water or high pressure harnesses the power of sound waves, slashing time and energy.
And, importantly for coffee drinkers, it tastes the same as a cup brewed the traditional way.
Coffee and beer are two beloved areas of scientific study. Here, UNSW Sydney researchers focus on brewing one of these beverages – espresso. They've used ultrasonic sound waves to produce espresso-strength coffee with room-temperature water.
Why mess with what's not broken? Well, the traditional way of getting this intense brew is far more energy-intensive than we might think when we swing by the coffee shop for our morning hit. Consider the cost of heating water, which is notoriously expensive thanks to water's ability to soak up thermal energy.
The team found that sound waves can replace the role of heat, cutting energy use by up to 75% compared with the tried-and-true way.
The energy savings could be particularly useful when scaled at a commercial level, such as companies making shelf-stable ready-to-drink blends that still use the traditional method to make their product. It also significantly reduces brewing time.
“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 Francisco Trujillo, from UNSW’s School of Chemical Engineering.
“Traditionally, espresso is made 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 randomized test, they could not tell it apart from a normal espresso," he adds.
In blind taste tests, participants couldn't tell the difference between espresso brewed using sound waves and espresso brewed using high temperatures – both produced the same deep, rich taste consumers expect.
Trujillo has already used the patented ultrasound system to make cold-brew coffee – which, if you've ever put down a batch yourself, you'll know it is either an overnight or all-day process. The scientists here can do it in just three minutes.
But cold brew compared with espresso is apples and oranges in the coffee world. Espresso is more concentrated and rich, with a lot more caffeine bang for your buck. So it was another task entirely to put the ultrasonic method to use on this kind of coffee.
“We have been working on a range of parameters to discover how to make the perfect ultrasonic espresso,” says Trujillo. “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," he adds "We found that by grinding finer we could extract the flavour more rapidly."
A regular filter basket becomes the "ultrasonic reactor" that brews ground beans, using high-frequency sound waves to unlock the flavor, aroma, and body of what we know as true espresso coffee. Inside the system, a transducer produces the ultrasonic waves, making the grind-filled basket and water vibrate rapidly.
This produces acoustic cavitation, where microscopic bubbles form and collapse in the liquid. When the collapse occurs near the coffee, the researchers say they act like tiny jets of liquid that fracture the grounds and unlock the transformation.
As the surface of coffee particles breaks open, flavor compounds, oils, and caffeine move into the water; something that is traditionally temperature-dependent if you want it done quickly, like with brewing espresso shots.
"We also experimented with how long the sound waves were applied, as this can affect both the concentration and flavour of the coffee," Trujillo says. "What we found is that between two-and-a-half and three minutes is a sweet spot for producing a balanced cup.”
In a blind sensory test featuring nearly 100 participants, four coffee types were consumed – traditional espresso, ultrasound-brewed espresso, traditional filter and ultrasound-brewed filter. To control the evaluation, all were cooled to the same temperature, served in identical vessels and presented randomly.
The participants were just regular coffee drinkers who consumed at least one cup a week. And we imagine the researchers had no shortage of volunteers on a university campus.
The testers scored the drinks on a nine-point scale, assessing aroma, flavor, bitterness, and overall likability.
The consumers found no significant differences between the traditional and ultrasound espresso, with drinkers unable to pick out the ultrasound brew. For the filter-coffee samples, participants significantly preferred the ultrasound cup overall, which also scored favorably when it came to bitterness, compared with the traditional brew.
“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,” says Trujillo.
Given the relative simplicity of the system, the ultrasound method could be implemented in home coffee machines. However, the researchers believe, given the energy savings, the real win could be on a commercial level.
“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," says Trujillo. “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," he adds.
The research was published in the Journal of Food Engineering.
Source: UNSW Sydney
Fact-checked by Mike McRae
