Science & Technology, Australia (Commonwealth Union) – Engineers from the University of New South Wales, have dramatically reduced the time required to make cold brew coffee, cutting it from many hours to mere minutes by using sound waves.
Cold brew coffee enthusiasts appreciate its smoother, less acidic, and less bitter taste compared to regular hot brew. However, the traditional method of making cold brew is time-consuming, taking 12 to 24 hours to fully steep the grounds and extract the flavors using only cold water. This lengthy process is inconvenient for those needing a quick caffeine fix.
Now, UNSW engineers have developed a method to produce cold brew coffee in under three minutes, matching the speed of a regular hot brew, without compromising on taste.
The breakthrough involves using an ultrasonic reactor to accelerate the brewing of the ground coffee beans, as detailed in research that appeared in Ultrasonics Sonochemistry.
To tackle the challenge of speeding up the cold brew process, the UNSW team, led by Dr. Francisco Trujillo, adapted a Breville espresso machine with their own patented sound transmission system. This system integrates a bolt-clamped transducer with the brewing basket via a metallic horn, converting a standard espresso filter basket into a powerful ultrasonic reactor.
The reactor operates by injecting sound waves at a frequency of 38.8 kHz at multiple points through its walls, creating several regions of acoustic cavitation inside the reactor.
The study also found that this method can double both the extraction yield and caffeine concentration compared to samples that were not subjected to ultrasound treatment.
Dr. Trujillo, the corresponding author of the paper and a food processing engineer at UNSW’s School of Chemical Engineering, explains that the ultrasound process significantly speeds up the extraction of oils, flavors, and aromas from ground coffee.
He pointed out that ultrasound accelerates the extraction process through a phenomenon known as acoustic cavitation.
Dr. Trujillo stated that when acoustic bubbles collapse near the ground coffee, they generate micro-jets with sufficient force to pit and fracture the coffee grounds, thereby intensifying the extraction of the brew’s aroma and flavors.
He further indicated that the acceleration is remarkable – we are reducing a process that would typically take 12 to 24 hours to less than three minutes.
Dr. Trujillo stated that their goal was to make the procedure as simple as making a normal espresso coffee.
“We’re able to demonstrate that this can be adapted to existing espresso machine,” he explained.
“We are very excited about developing this technology that can be used by companies that already manufacture coffee machines, so consumers can enjoy an ultrasonic cold brew at home in less than three minutes.
“Very importantly, this breakthrough opens the door for coffee shops and restaurants to produce on-demand brews comparable to 24-hour cold brews, supplying the rising demand while eliminating the need for large semi-industrial brewing units and the associated requirement for extensive refrigeration space.”
As they joined hands with researchers from the University of Queensland, coffee samples were sent to the Queensland Alliance for Agriculture and Food Innovation (QAAFI) for an in-depth sensory analysis.
The samples included a cold brew sonicated at room temperature for one minute, another sonicated for three minutes, and a traditional cold brew steeped for 24 hours at four degrees Celsius without sonication.
These samples were evaluated based on their aroma, texture, flavor, and aftertaste.
Dr. Trujillo then indicated that when compared to the 24-hour brew, the sonicated one-minute brew received similar ratings, particularly in flavor and aftertaste attributes such as bitterness, sourness, fullness, texture, and aroma.
However, it scored lower in aroma intensity and dark chocolate aroma, suggesting that the one-minute sonicated sample is slightly under-extracted when contrasted with the 24-hour cold brew.
According to Professor Heather Smyth, a sensory scientist and flavor chemist at the University of Queensland and co-author of the study, the new method produces coffee that rivals cold brew steeped overnight.
Professor Smyth explained their trained sensory panel tastings demonstrated that they can achieve a taste profile very similar to both traditional cold brew and espresso within the time it takes to brew a hot espresso.
Ultrasound technology has various applications in the food industry, enhancing processes such as drying, extraction, emulsification, and crystallization, making them quicker with greater efficiency.
According to Dr. Trujillo, this technology can also be utilized to accelerate the brewing process of teas.
