For many coffee lovers, making espresso seems to require two essential ingredients: very hot water and high pressure.
But researchers at the University of New South Wales (UNSW) in Australia have challenged that assumption by creating espresso-strength coffee using room-temperature water and ultrasonic sound waves.
The new technique could reduce the energy needed to make coffee by up to 75%, while still producing a drink with the flavor, aroma, body, and caffeine content of traditional espresso.
The research, published in the Journal of Food Engineering, found that most coffee drinkers could not tell the difference between the new “ultrasonic espresso” and a regular espresso.
The project was led by Dr. Francisco Trujillo and his team from UNSW’s School of Chemical Engineering. Their system uses ultrasound, which consists of sound waves at frequencies too high for humans to hear.
Traditionally, espresso is made by forcing hot water through finely ground coffee beans under high pressure. Heating the water accounts for a significant portion of the energy required during brewing.
The UNSW team wanted to find a way to achieve the same result without using heat.
Their solution was to transform a standard coffee filter basket into an ultrasonic reactor. A small device called a transducer is attached to the side of the basket. When activated, it generates ultrasonic vibrations that travel through both the coffee grounds and the water.
These vibrations create a process known as acoustic cavitation. Tiny bubbles form and collapse rapidly within the water. As these microscopic bubbles burst near the coffee particles, they act like tiny cleaning brushes or jets, breaking open the surface of the coffee grounds.
This process allows flavor compounds, oils, and caffeine to move into the water much faster than they normally would at room temperature.
As a result, the researchers were able to produce a concentrated coffee similar in strength to espresso in less than three minutes.
The team spent considerable time fine-tuning the brewing process. They experimented with different coffee-to-water ratios, grind sizes, and brewing times. They found that using finely ground coffee and applying ultrasound for between two and a half and three minutes produced the best balance of flavor and concentration.
To see whether consumers would notice any difference, the researchers conducted blind taste tests involving around 100 regular coffee drinkers. Participants sampled four different drinks: traditional espresso, ultrasonic espresso, traditional filter coffee, and ultrasonic filter coffee.
The results surprised the researchers. Participants found no significant differences between the traditional and ultrasonic espresso. Most people could not reliably identify which one was made with sound waves and which one was brewed using conventional methods.
Even more interesting, the ultrasonic version of filter coffee was actually preferred by many participants, who rated its bitterness as more pleasant.
The researchers believe the technology could eventually be used in home coffee machines. However, the greatest opportunity may be in large-scale commercial production.
Companies that manufacture ready-to-drink coffee beverages could use the system to reduce energy costs and speed up production. Because the process creates a concentrated espresso-strength coffee, it could also be used to produce coffee concentrates for bottled drinks, cold brews, and milk-based beverages.
If the technology proves successful on a larger scale, your future espresso might owe more to sound waves than boiling water.
