Colombian researcher Francisco Trujillo leads a team at the University of New South Wales, Australia, who claim to have invented what they call “ultrasonic espresso.” As Trujillo explains, it’s “a room temperature brewing process that uses high-frequency sound waves to extract flavors, oils, aromas, and caffeine from ground coffee.”
Although the process takes longer than the traditional 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 coffee in industrial quantities, such as those making ready-to-drink products.
Sonic Brew
The experimental system directs ultrasonic waves directly into a filter containing ground beans in water. Instead of relying on heat, the technology uses a phenomenon called 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 coffee.
To generate those microscopic currents, the scientists designed a device capable of transmitting ultrasonic vibrations throughout the entire filter basket, turning it into a kind of acoustic reactor. This design allows the waves to strike multiple points simultaneously and accelerate the movement of the fluid around the coffee particles. “Ultrasound helps us convert heat into mechanical energy,” explains Trujillo.
The goal of this entire process, which is described in more detail in this month’s issue of the Journal of Food Engineering, is to achieve a concentration equivalent to that of an espresso. To do this, the researchers adjusted variables such as grind size, ultrasound power, and brewing time. Using a fine grind and 100 watts of power, they achieved beverages with dissolved solids levels and extraction yields that are comparable to those considered ideal by the Specialty Coffee Association.
When the experiments were repeated under similar conditions but without ultrasound, it was not possible to obtain these values. The ultrasonic system made it possible to produce coffee of the same intensity as espresso in just a few minutes – the researchers found the optimum time to be between two and a half to 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 the overall composition of volatile compounds responsible for aroma.
taste test
A group of 100 people took part in sensory tests in which they compared ultrasonic espresso to traditional espresso. Ultimately, participants showed no significant preference for any method. The scores for aroma, taste, bitterness and overall acceptance were almost equal.
They also compared filtered coffee prepared using the traditional method and ultrasound. “In the case of filtered coffee, the ultrasonically processed version was generally preferred, and participants rated its bitterness as more pleasant,” Trujillo said.
In addition to mimicking the sensory characteristics of espresso, the new technology could provide environmental benefits. Measurements taken by the researchers indicated that, to produce beverages of the same intensity, the ultrasonic system used only 24 percent of the energy consumed by a typical espresso machine.
The authors emphasize that coffee produced using ultrasound is not the same as traditional espresso. However, the results show that it is possible to produce beverages with comparable chemical and sensory characteristics without heating water.
This research opens up the possibility of developing new coffee makers capable of preparing everything from espresso to filtered coffee and cold brew using the same technology. If these systems are ever brought to market, the distinctive sound of the espresso machine may be replaced by the inaudible vibrations of ultrasound.
This story was originally published by WIRED en Español and is translated from Spanish.
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