Ultrasound is Changing the Cold Brew Game

Cold brew ready in minutes? What once seemed impossible is now becoming reality with ultrasonic technology.

BY BHAVI PATEL
FOR BARISTA MAGAZINE

Photos courtesy of Bhavi Patel unless otherwise noted

What to know:

• Researchers are experimenting with ultrasound-brewed coffee, using an ultrasonic reactor setup to make cold brew in minutes
• The technology has the potential to reduce the cold brew-making process to under three minutes, also helping cafés save on storage space

It’s a hot summer afternoon, and you walk into a café hoping to unwind over a glass of cold-brew coffee. You approach the barista at the counter and say, “I would like a cold brew please,” and you pay and step aside for the next customer. But you’re distracted because the barista isn’t pouring your cold brew from a pitcher or pulling a tap; they’re making shots at the espresso machine instead.

“Actually, I wanted a cold brew, not an espresso,” you say to the barista. But they only smile and assure you that your cold brew is coming right up. Just a few minutes later, they serve you your cold brew—which came from the espresso machine.

Nope, this isn’t a sci-fi movie. A research paper published in April 2024 authored by researchers from the University of South New Wales, University of Sydney, and University of Queensland, details findings about the on-demand production setup for cold brew in under three minutes.

The setup uses an ultrasonic reactor for fast production, and the resulting cold brew made from coffee pulled as espresso, the paper attests, is indistinguishable from a 24-hour cold brew.

The cold-brew market has seen steady growth globally, rising from $0.32 billion to $1.37 billion between 2017 and 2023. With surging demand, cafés will need to increase cold-brew production to keep up, requiring bigger tanks and more storage space, including larger refrigeration spaces.

Space is a major limiting factor for most cafés, which presents quite a challenge. Moreover, making cold-brew coffee using traditional methods takes hours and requires efficient pre-planning and resource management.

Enter ultrasound

Coffee consultant and the man behind the Little Guy Stovetop Espresso Maker, Craig Hiron, came across the potential of ultrasound to improve coffee extraction. He approached researchers, discussed the idea, and after about five years of trial and error, his sonoreactor was perfected and patented.

Ultrasound creates tiny acoustic bubbles, also called inertial bubbles, which accelerate the extraction due to acoustic cavitation. When the bubbles collapse near solid materials like coffee grounds during extraction, they generate micro-jets with the force to fracture the cell walls of plant cells, intensifying the extraction of coffee.

Multiple studies have explored ultrasound’s potential to enhance and expedite coffee brewing. However, they generally used the traditional ultrasonic baths and horns that aren’t very practical for commercial implementations.

This is where this new research takes a step further toward practical commercial application. The ultrasonic coffee-brewing system uses a patented sound transmission system that connects a bolt-clamped Langevin transducer with the coffee-brewing basket of a standard espresso machine via a metallic horn. This transforms the coffee basket into a powerful ultrasonic vessel, characterized by acoustic streaming, resulting in rapid and efficient brewing. You get a cold brew in under three minutes that maintains nearly indistinguishable sensory attributes compared to a standard 24-hour cold brew.

“We modified a Breville Dual Boiler BES920 espresso machine to sonicate during brewing by placing a transducer-horn assembly comprising a 28 kHz bolt-clamped Langevin transducer and a horn. The horn transmits ultrasound from the transducer to the filter basket,” says Francisco Trujillo, one of the authors of the paper. “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.”

The process

First, coffee is ground to a fine espresso grind and dosed. Once the portafilter is inserted, the transducer-horn assembly is engaged. Water is pre-infused for about four seconds at a pump speed of 700rpm. When properly connected, the portafilter head seals the contents of the filter basket, with back pressure retaining most of the liquid in the filter basket during brewing.

Next, the engaged transducer-horn assembly applies 100W of sonication to produce the brewed coffee. Once the extraction is completed, the transducer-horn assembly is moved from the brewing position to the storage position. The portafilter containing the spent coffee grounds can now be removed.

“This method of making ultrasound coffee works best for a roast between a filter and an espresso roast, like a very light espresso roast or a medium-roasted coffee,” says Craig. The fullness of the filter basket or the basket loading percentage (the mass of coffee in the basket as a percentage of the basket’s capacity) also affects the final brew, especially its color intensity, extraction yield, caffeine concentration, and fatty acid concentration.

“The efficiency of the extraction increased by decreasing the basket loading percentage,” adds Francisco.

The results

The ultrasound-brewed coffee exhibited sensory attributes almost identical to 24-hour cold brew. When sensory experiments were done on three samples—a one-minute sonicated brew at ambient temperature; a three-minute sonicated brew at ambient temperature; and an unsonicated cold brew at 4° Celsius for 24 hours—promising results were found.

The one-minute sonicated brew had similar ratings for flavor and aftertaste attributes—including bitterness, sourness, fullness texture, and ashy aroma—to the 24-hour unsonicated brew. However, it scored lower on aroma intensity and dark chocolate aroma.

The three-minute sonicated brew had similar ratings to the 24-hour brew, but it also had greater bitter and sour flavors and aftertaste. The three-minute sample could be considered slightly over-extracted compared to the 24-hour brew. Hence, a sonication time between one and three minutes would be ideal for creating a coffee closest in cup profile to the 24-hour cold brew.

From proof of concept to commercial convenience

This revolutionary technology is a promising proof of concept that cold brew can be made fresh in minutes. This breakthrough could enable coffee shops and restaurants to produce on-demand brews comparable to 24-hour cold brew, eliminating the need for semi-industrial brewing units and the associated requirement for extensive refrigeration space. With the rising popularity of cold-brew coffees, this could be game-changing.

Could the transducer assembly be retrofitted to existing espresso machines with a new modified portafilter? Researchers say, at this point, probably not. The team behind this innovation is looking to partner with commercial equipment manufacturers to take the tech commercial and build a new range of espresso machines with the transducer assembly built in and ready to use.

The calibrations would ideally be done based on the café/buyer requirements. Once the tech goes commercial, waiting for hours and lifting heavy tanks to get the cold-brew supply ready for use could become a distant memory. The innovation also opens doors for further research in applying this technology to other food products like tea.

This article originally appeared in the October + November 2024 issue of Barista Magazine. Read more of the issue online here for free.

ABOUT THE AUTHOR

Bhavi Patel is a food writer focusing on coffee and tea, and a brand-building specialist with a background in dairy technology and an interest in culinary history and sensory perception of food.

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