If you appreciate good coffee in a hurry, you’ll love the sound of this. UNSW Sydney engineers have utilised sound waves to cut down the time for cold brew coffee extraction from 24 hours to just three minutes.
You would think the perfect cup of coffee would be the creation of expert baristas, but it is a team of biochemical engineers who have found a way to deliver the flavour of a cold brew with the speed of an espresso.
Cold brew is a favourite of coffee aficionados because the slow extraction reduces acidity and bitterness, resulting in a smoother, richer flavour and enhanced caffeine content. This method of steeping coarse grounds in cold water can take up to 24 hours. Not anymore, thanks to Dr Francisco Trujillo and his team at UNSW who have amplified the process.
Embracing the challenge of making a cold brew in the same time it takes to pour a coffee shot, the team used an existing model of a Breville Dual Boiler BES920 espresso machine and superimposed their own patented sound transmission system. It 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 reactor works by injecting sound waves at a frequency of 38.8 kHz at multiple points through its walls. When acoustic bubbles collapse near the ground coffee, they generate micro-jets of liquid with enough force to pierce and fracture the grounds in a phenomenon called acoustic cavitation.
As Trujilo reveals, a complex cup of coffee warrants complex technology. "A Fluid-o-Tech GA rotary vane pump with a 24V DC brushless motor was used to pump water into the coffee basket. The original boiler in the Breville machine was used but was controlled independently with an integrated circuit, allowing better temperature and time management. A UI programmed in Python was developed and connected to a laptop to control the brewing parameters."
According to the research, this setup can double the extraction yield and caffeine concentration as well as increase the extraction of coffee oils eightfold. The superior sensory attributes are due to the higher oil and volatile content. The resulting elixir is opaque, caramel coloured and highly viscous. It has the concentration and convenience of an espresso, but sweetness, depth and fruity notes of a gradually extracted cold brew.
This new super brew has caught the attention of the science world and has the coffee industry positively frothing. The research paper has been published in Ultrasonics Chemistry and featured in New Scientist, Science Direct and Labdownunder. A reporter for The Guardian described the tasting experience as "like drinking a music festival.” The world’s number one coffee magazine Global Coffee Report has heralded the invention as the future of brewing, while Barista Magazine described it as a game changer in cold brew.
Trujillo’s enthusiasm for exploring this richly flavoured territory is clear.
There’s nothing like it. The flavour is nice, the aroma is nice and the mouth feel is more viscous. There’s less bitterness than a regular espresso shot and it has a level of acidity that people seem to like. It’s now my favourite way to drink coffee.
The research found sonication increased the level of both triglycerides and caffeine in the coffee. The triglycerides, or lipids, are essentially the fats inside the coffee grounds and play a large part in the aroma and flavour of the coffee. In an espresso, the triglycerides can be seen in what is called the ‘crema’, the foam that floats on top of a typically black beverage. But the application of ultrasound emulsifies the triglycerides with the beverage, mixing them together.
“Ultrasound brewing almost doubled the amount of lipids in the coffee. The lipids form a stable emulsion so you’re not going to see a crema going to the top and bursting like you see in an espresso. The look will be different; it will be richer in triglycerides and richer in aroma,” Dr Trujillo explains.
Like many of the world’s great inventions, this supersonic coffee was the unexpected result of experimentation. Initially, Trujillo was collaborating with Craig Hiron, entrepreneur and owner of Little Guy Stovetop Coffee Maker, to find a way to raise the level of antioxidants in a cup of coffee. This involved a large semi-industrial ultrasonic unit that wouldn’t even fit on a kitchen bench. While they didn’t find any discernible difference in the levels of antioxidants, they knew they had come across an incredible cup of coffee.
“I wasn’t able to mask my excitement at the discovery. I shouted: ‘Look at this colour, look at this flavour, look at this creaminess,” Hiron reveals. The unexpected but promising results encouraged Trujillo to research the relationship between coffee and ultrasonic waves. After some initial prototyping he began working with Professor Kourosh Kalantar-Zadeh, current lead of the School of Chemical and Biomolecular Engineering at the University of Sydney, to simplify the technology and process.
The adapted Breville coffee machine is not only much more compact and convenient, but the invention has the potential to revolutionise coffee culture. Trujillo has plans to commercialise and license the ultrasonic coffee brewing technology with major coffee machine manufacturers, with a provisional patent already in place.
He acknowledges ultrasonic coffee machines will be slightly more costly than traditional models, but he would like it to remain commercially viable as his research has already demonstrated it can be adapted to an existing espresso machine with a low-cost investment. It could also enable cafes and restaurants to produce on-demand brews comparable to traditional 24-hour cold brews. This would eliminate the need for semi-industrial brewing units and the associated requirement for extensive refrigeration space.
Obviously a coffee fan himself, Trujillo considers the discovery a “blessing from heaven. Imagine how sad it would have been if, after five years of hard work, the coffee ended up being boring. Fortunately, it wasn’t,” he says. “The ultrasonic coffee is rich, bold, and clean, with a fantastic fruitiness, texture, and flavour.”
The published research paper, “Coffee brewing sonoreactor for reducing the time of cold brew from several hours to minutes while maintaining sensory attributes” can be read online here.