Scientists Brewed Espresso With Sound Waves and Nobody Could Tell

For as long as espresso has existed, the formula has been the same: hot water, around 90 to 95 degrees, forced through a tightly packed puck of fine coffee at roughly 9 bar of pressure. That combination of heat, pressure and short extraction time is what gives espresso its body, its crema and its concentration. But recently it's been discovered that this isn't the only way to get there.

Researchers at UNSW Sydney's School of Chemical Engineering have published a study showing they can produce espresso strength coffee using room temperature water and ultrasonic sound waves instead of heat. No boiler, no high pressure pump, just a modified portafilter basket fitted with an ultrasonic transducer. The coffee comes out in two to three minutes, and in blind taste tests, regular coffee drinkers could not reliably tell it apart from the real thing.

This is the kind of breakthrough that's worth sitting with for a minute, because it pokes at an assumption most of us in coffee have never really questioned: that you need heat and pressure to extract espresso properly.

How Do You Brew Espresso Without Heat?

The team, led by Dr Francisco Trujillo, built a system that turns the filter basket into what they're calling an ultrasonic reactor. High frequency sound waves, well above what humans can hear, are fired into the coffee grounds and water while they sit at room temperature. Instead of the high-pressure centrifugal pump conventional machines use, the system uses a positive displacement gear pump to manually dose water through the basket in cycles, with the ultrasound doing the actual work of extraction.

The mechanism at play is something called acoustic cavitation. The sound waves cause microscopic bubbles to form in the water, and when those bubbles collapse near the coffee particles, they act a bit like tiny scrubbing brushes. They fracture and pit the surface of the grounds, which lets flavour compounds, oils and caffeine move into the water far faster than they would at that temperature without any agitation at all.

In other words, the ultrasound is doing a job that heat normally does. It's just doing it mechanically instead.

The researchers found a few variables mattered most in dialling this in, as Trujillo explained in the UNSW press release. Brew ratio, meaning how much water per gram of coffee, had to be tight enough to avoid a diluted result. Grind size mattered too, with finer grounds extracting faster under ultrasound. And timing landed in a fairly narrow window, with two and a half to three minutes producing the most balanced result.

For reference on grind, anyone running a Comandante at home knows how sensitive extraction is to even small grind changes on a normal machine. It's interesting that ultrasound brewing appears to have its own, separate sensitivity to grind, rather than simply removing the variable.

The Taste Test

Good science doesn't mean much in coffee until it's been through a cup. UNSW ran a blind sensory evaluation with around 100 regular coffee drinkers, not trained cuppers, just people who drink coffee at least weekly. Four drinks were poured: traditional espresso, ultrasonic espresso, traditional filter, and ultrasonic filter. All were brewed fresh, cooled to the same temperature and served in identical, randomised, unmarked cups.

Participants rated each on aroma, flavour, bitterness and overall liking using a nine point scale. For the espresso comparison, there was no statistically significant difference across any of those measures. Most people could not consistently pick which was which, and there was no overall preference for one method over the other.

The filter coffee result was arguably even more interesting. Participants actually rated the ultrasonic filter coffee's bitterness more favourably than the traditional version, suggesting the technique might do more than just replicate existing brews. It may, in some cases, improve on them.

The Numbers Behind the 75 Percent Energy Claim

The headline energy figure is real, and the study backs it with measured data rather than estimation. Producing three beverages at matched strength, around 8.7 to 8.9 percent TDS, over a 20 minute window, the ultrasonic system used 0.020 kWh compared to 0.0823 kWh for a conventional single group espresso machine. That's roughly a quarter of the energy, or close to a 75 percent reduction.

It's worth noting those figures exclude the startup heating cycle of the conventional machine, which the researchers point out matters more for someone switching their home machine on for one shot than it does for a cafe running a machine continuously through service.

There's also a genuinely surprising extraction yield finding buried in the data. At the finest grind setting tested, around 325 microns, ultrasonic brewing at room temperature hit 18.03 percent extraction yield, which sits inside the range generally considered optimal. Without ultrasound, the same grind under otherwise identical conditions only reached 16.26 percent. Across every grind size tested, the no-ultrasound control never reached optimal extraction at all. That's a striking result on its own, separate from the energy story, because it suggests ultrasound isn't just an efficient alternative to heat and pressure, it may genuinely extract more effectively at low temperature and low pressure than plain water agitation can.

Why This Matters

We're not going to pretend this means your espresso machine is obsolete. It isn't, and the researchers themselves are framing this primarily as an industrial and commercial opportunity, particularly for companies producing ready to drink coffee or concentrate at scale, rather than a like for like replacement for a home setup.

But as a piece of science, this is a genuine challenge to an assumption a lot of us in specialty coffee treat as settled. We talk about heat and pressure as the non negotiables of espresso. This study shows us that what actually matters is getting enough energy into the coffee bed to drive extraction and that energy doesn't have to arrive as heat or hydraulic pressure. It can arrive as mechanical agitation instead.

Whether ultrasonic systems ever show up on a cafe counter or in a home kitchen is a separate question and one that depends on cost, durability, consistency and whether the result holds up outside a lab with a wider range of beans, roast profiles and other variables. The fact that ultrasound only outperformed traditional brewing's extraction yield at certain grind sizes also suggests this is still an early stage process, not a finished product. But it's a reminder that the way we've always brewed espresso is one solution to the extraction problem, not the only one.

Source: Trujillo et al., published in the Journal of Food Engineering, June 2026. Read more from UNSW Sydney and Dr Trujillo's own write-up for The Conversation.