Espresso Without Hot Water: Ultrasound Reduces Energy Consumption by Up to 75%

Preparing an espresso without using hot water might seem counterintuitive, but a group of researchers from UNSW Sydney claims to have demonstrated otherwise. The study, published in the Journal of Food Engineering, describes an extraction system that utilizes high-frequency ultrasonic waves to achieve coffee with a concentration, aromatic profile, and caffeine content comparable to that of traditional espresso, while using water at room temperature.

According to the team led by Dr. Francisco Trujillo from the School of Chemical Engineering, the new approach allows for an energy consumption reduction of up to 75% compared to conventional methods. The advantage mainly arises from eliminating the water heating phase, one of the most energy-consuming components in espresso preparation.

To develop the process, the researchers modified a traditional filter basket, transforming it into an ultrasonic reactor. A metallic transducer capable of generating sound waves at frequencies well beyond the threshold of human hearing is applied to the side of the container. The vibrations propagate simultaneously through the water and ground coffee, triggering the phenomenon of acoustic cavitation. Effectively, tiny microscopic bubbles form and collapse rapidly inside the liquid, acting as high-energy micro-jets. This process causes the superficial fracturing of coffee particles and accelerates the transfer of aromatic compounds, oils, and caffeine into the water.

The result is a much more efficient extraction than that typically achievable with cold water. The entire process takes less than three minutes and allows for concentrations typical of traditional espresso.

The authors explain that achieving results comparable to classic espresso required extensive optimization work. Among the most important factors were the coffee-to-water ratio, grind size, and duration of ultrasound exposure. Finer grinding facilitated faster extraction of desired compounds, while the optimal treatment time was found to be between two and a half and three minutes. Beyond these values, variations in concentration and flavor profile of the beverage can emerge.

To assess the quality of the obtained product, the research group organized a double-blind sensory evaluation involving around 100 regular coffee consumers. Participants tasted four different drinks: traditional espresso, espresso made using ultrasound, conventional filtered coffee, and filtered coffee prepared with the new technology. All drinks were served at the same temperature, in identical containers, and in random order to minimize potential bias. Participants rated aroma, taste, bitterness, and overall liking using a nine-point scale.

The results showed that, in the case of espresso, no statistically significant differences emerged between the traditional and ultrasonic methods. In other words, most consumers were unable to identify which sample was prepared without hot water. Interestingly, the result obtained in the filtered coffee category showed that the ultrasound-produced version received overall better ratings, particularly appreciating a perceived bitterness judged to be more pleasant.

Although the technology could theoretically be integrated into future home coffee machines, the researchers believe that the most interesting opportunities lie in industrial production. Companies that produce ready-to-drink coffee beverages could benefit from both reduced energy consumption and processing speed. The system indeed produces a high-concentration extract that can be used directly in ready-to-drink products or transported as a concentrate and later diluted to create other commercial preparations.