A UNSW team, led by Dr Francisco Trujillo, has reduced the time it takes to make cold brew coffee from 24 hours to three minutes using ultrasonics – adding their patented sound transmission system onto an existing Breville espresso machine.
Cold brew coffee is characterised by a smoother, less acidic, and less bitter taste compared to a regular hot brew, but it takes 12 to 24 hours to fully steep the grounds and extract the flavours.
However, engineers from UNSW Sydney have now developed a new way to make cold brew coffee in under three minutes, without sacrificing on the taste.
The system connects a bolt-clamped transducer with the brewing basket via a metallic horn – transforming a standard espresso filter basket into a powerful ultrasonic reactor.
The process involves using an ultrasonic reactor to speed up the brew of the grounded coffee beans, by injecting sound waves at a frequency of 38.8 kHz through its walls – generating multiple regions for acoustic cavitation within the reactor.
Dr. Trujillo, corresponding author of the paper and UNSW food processing engineer in the School of Chemical Engineering, says the ultrasound process speeds up the extraction of the oils, flavours and aroma of the ground coffee.
“Ultrasounds accelerate the extraction process due to acoustic cavitation. When acoustic bubbles collapse near the grounded coffee, they generate micro-jets with enough force to pit and fracture the coffee grounds – intensifying the extraction of the aroma and flavours of the brew.
The study also found that this setup can double the extraction yield and caffeine concentration compared to non-sonicated samples.
“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,” said Dr Trujillo.
“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.”
Collaborating with researchers from University of Queensland, samples of coffee were sent to the Queensland Alliance for Agriculture and Food (QAAFI) where they underwent a thorough sensory analysis on aroma, texture, flavour, and aftertaste attributes.
The samples included cold brew sonicated at room temperature for one minute, the second was sonicated for 3 minutes, and the third was a regular brew, steeped for 24 hours at four degrees Celsius.
“Compared to the 24-hour brew, the sonicated one-minute brew sample received similar ratings, especially in flavour, aftertaste attributes including bitterness, sourness, fullness texture and aroma,” says Dr. Trujillo.
“However, it scored lower in aroma intensity and dark chocolate aroma. This suggests that the sonicated 1-minute sample is slightly under-extracted compared to the 24-hour cold brew.
“Meanwhile, the sonicated three-minute sample provided a similar dark chocolate aroma and aroma intensity to the 24-hour cold brew, but slightly more bitter.
“The results of the sensory study showed that a sonication time between one and three minutes is ideal for creating a coffee comparable with 24-hour cold brew coffee, depending on the interest of customers.”
University of Queensland sensory scientist and flavour chemist Professor Heather Smyth, a co-author of the paper, said the new method created a coffee as good as cold brew steeped overnight.
“Once again, Australia has new technology at our fingertips that moves on from traditional methods to modern methods of coffee making to give consumers a new premium experience.
“Further work could explore different types of beans, different regions of beans and for companies or cafes that specialise in single origin or high-quality beans, this would be another string to the bow to show yet another dimension of coffee.”
