Scientists Invent Ultrasonic Espresso Method Without Hot Water

What do you need to make a good espresso? Ground coffee, of course; a machine capable of generating pressure; and hot water, preferably heated to between 195 and 205 degrees Fahrenheit. And that's it.

But could one perhaps do without that last element? No, not the water itself, but the need to heat it. The Colombian researcher Francisco Trujillo led a team at Australia's University of New South Wales that claims to have invented what it calls "ultrasonic espresso." As Trujillo explains, it is "a room-temperature brewing process that uses high-frequency sound waves to extract the flavor, oils, aroma, and caffeine from ground coffee." Although the process takes longer than the conventional method (three minutes versus 30 seconds), it consumes 75 percent less energy—a considerable benefit for coffee shops and restaurants, but especially for businesses that produce industrial quantities of coffee, such as those making ready-to-drink products.

The experimental system directs ultrasonic waves directly into the filter containing the ground beans in water. Instead of relying on heat, the technology harnesses a phenomenon known as acoustic cavitation. This involves the formation and collapse of tiny bubbles that generate microcurrents which, in this experiment, facilitate the extraction of soluble compounds from the coffee.

To generate those microcurrents, the scientists designed a device capable of transmitting ultrasonic vibrations throughout the entire filter basket, transforming it into a sort of acoustic reactor. This design allows the waves to hit multiple points simultaneously and accelerate the movement of liquids around the coffee particles. "Ultrasound helps us replace heat with mechanical energy," explains Trujillo.

The goal of this entire process, described in greater detail in this month's issue of the Journal of Food Engineering, is to achieve a concentration comparable to that of an espresso. To do so, the researchers adjusted variables such as grind size, ultrasound power, and brewing time. Using a fine grind and 100 watts of power, they obtained beverages with levels of dissolved solids and extraction yields equivalent to those considered ideal by the Specialty Coffee Association.

When the experiments were repeated under the same conditions but without ultrasound, it was not possible to achieve these values. The ultrasonic system made it possible to produce coffee with an intensity similar to that of espresso in just a few minutes—the researchers found the optimal time to be between two and a half and three minutes—using water at room temperature. The team also analyzed various chemical parameters.

The concentrations of caffeine and chlorogenic acid were similar to those obtained by conventional methods. No significant differences were observed in pH or in the overall composition of the volatile compounds responsible for the aroma. A group of 100 people participated in sensory tests in which they compared ultrasonic espresso with conventional espresso.