How does ultrasound affect flow rate? Do fines sink to the bottom of the puck and choke the shot?
There is a new movement happening, especially in lighter roast coffees, where we're finding that more balanced extractions (less bitterness/acidity/acridity) are happening at lower pressures, even going so far as grinding so coarse that the puck offers zero resistance - effectively making the pump the limiting factor for flow rate. Light roast coffee is much less porous and more hydrophobic.
I wonder if adding ultrasound would allow light roasts to yield more extraction in general, maybe even keeping the high temperature. Or, would adding ultrasound allow a finer grind size and more resistance without adding the harsh flavors of a high-temperature shot.
So many experiments to be done!
Where's James Hoffmann when you need him?
But perhaps this can be used in the instant coffee industry or something.
TL;DR: Aiming for a high-volume industrial goal, tone-deaf to coffee enthusiasts.
[1]: https://www.unsw.edu.au/newsroom/news/2024/05/Ultrasonic_col...
> It is noted that espresso is normally consumed hot and has transient sensory attributes that are temperature- and time-dependent. Hence, serving espresso at 22 °C will alter its sensory characteristics.
This is a weird test, coffee get’s so much worse when cold. So people can’t distinguish between two bad coffees.
Coldbrew is a thing and done right it brings out a refreshing sweetness. Also iced coffee. Bad coffee is bad hot or cold.
I like the ritual of it, for sure, but I'm not sure that's what makes it a good shot?
This is a myth. Bad coffee tastes better when hot because your sense of taste is dulled - reducing bitterness. Also, at higher temperatures, aromatics and volatile compounds are more airborne, improving the smell of coffee. Good coffee is better enjoyed around 60-70C
As stated in the article, the whole point is for use in ready-to-drink coffee manufacturing.
An average coffee shop's espresso machine might use $200/month of electricity, so even though the percent saving (75%) is high, it's off a base that's small relative to other costs; possibly too small to be enticing.
Cold drip coffee is a thing, done well a very nice thing.
Might be a new meta for iced lattes.
If you're drinking light, floral and acidic coffees, it's been relatively "trendy" recently to skim the crema off before drinking it.
I don't bother with that, but pulling two shots and removing the crema from one of them and trying them side by side is an interesting sensory experience — I'd encourage you to try, at least once!
(You might quibble whether it's actually espresso if there's not pressure and it's extracted cold; but it's closer to espresso in strength.)
Regardless, I would say it’s an objective fact that good coffee is ruined at room temperature. It still tastes fine, but no where near as good.
What especially irks me is that they could have just heated the stuff in a microwave [1] to 50°C and have a much better test.
It's not for you
An awful lot of people drink iced espresso drinks these days. Room temperature (or below) brewing would make a big difference to the dilution in those drinks.
There's a semi-famous, super hipster cafe near me in Tokyo, that I sometimes go to.
Once, they had a special on the menu, when they give you a flat white, and a double shot of espresso on the side, with a thermometer hovering over the shot, with suggestions of tasting notes that you can get out from sips at different temperatures.
Now, that's generally very much a thing — things definitely taste differently based on the temperature (or maybe _they_ don't, but we _perceive_ them differently? distinction without a difference, I guess.).
The suggested temperature ranges were 51-40C; 40-30C, and 30-20C.
51-40 was great. 40-30 was getting weird, but still _interesting_, because you definitely got different notes.
But the 30-20 was terrible. That is absolutely too cool to enjoy a shot of espresso. I'm all for experimentation and doing weird things, but that was no longer riding the line of "not great but interesting" and went straight into "why would you ever do this" territory.
But I also need my coffee: I'll drink whatever quality coffee is being offered, as long as it's the best I can get that morning.
Makes nice coffee, but I don’t think it’s worth the cost (but he has a lot of money, so it’s not a big deal for him).
I envision some fairly high-end kit, coming from this.
Technically you can also buy a bottle of grape juice from the grocery store, let it sit on the kitchen sink with a yeast lock for a few weeks and call it wine, and technically it even is, but it's also going to taste quite shitty.
You could just read the linked paper?
> Esp was prepared using a Sanremo Cube espresso machine. Brewing parameters were standardised following the supplier's guidelines: extraction time of 35 ± 3 s, pressure of 9 bar, and boiler temperature of 122 °C, with the corresponding group-head temperature of 94 ± 1 °C. A total of 21 g of ground coffee (GS = 2.6 ± 0.1; ∼262 μm) was placed in a ridged coffee basket and tamped using a constant-pressure tamper (MHW Flash Constant Pressure Tamper 2), applying 13.6 kg of force. The BR was reduced from 2 to 1.7 following the recommendations of the coffee roaster for better flavour (1 g of coffee grounds yielding 1.7 g of coffee brew).
1:1.7 is a bit short for my preferences (I like longer shots, usually aim for ~2.5); but otherwise that sure sounds like a pretty good double to me!
Researchers at UNSW Sydney have harnessed the power of ultrasonic sound waves to make espresso-strength coffee with room temperature water, cutting energy use by up to 75%.
That morning coffee kick from a shot of espresso needs boiling water and high pressure - equalling plenty of energy consumption, right?
Now, UNSW researchers have shown that one part of that recipe may not be essential: the hot water.
They have developed a completely new brewing process that uses room-temperature water to create an espresso-strength coffee with the same rich flavour, body and caffeine kick.
The process harnesses sound waves, and by not having to heat the water it reduces energy consumption by around three‑quarters. The saving could be especially significant for companies who make coffee-based ready-to-drink products at industrial scale, both in terms of energy use and brewing time.
Dr Francisco Trujillo and his team from UNSW’s School of Chemical Engineering have developed a system that uses ultrasound, high-frequency sound waves that are far above what a human can hear, to help extract the desired flavour, aroma and concentration from coffee grounds.
For enquiries about this story and interview requests please contact Neil Martin.
Email: n.martin@unsw.edu.au

Featured experts
Dr Francisco Trujillo with a cup of his new ultrasonic coffee. UNSW/Richard Freeman
Their research, published in the Journal of Food Engineering, included blind taste-testing experiments which showed that their ultrasonic room-temperature version of espresso was undistinguishable from coffee shots brewed in the traditional way.
“We call it an ultrasonic espresso. It’s a different process, but you get the same richness and concentration of a normal espresso in under three minutes,” says Dr Trujillo.
“Traditionally, espresso is by forcing hot water through coffee under pressure. But with ultrasound we can use room-temperature water instead, reducing energy consumption by up to 75%.
“And when we gave our ultrasonic espresso to 100 regular coffee drinkers in a randomised test, they could not tell it apart from a normal espresso.”
Dr Trujillo had previously developed the patented ultrasound system to create cold-brew coffee, which usually takes 12 to 24 hours to produce, in as little as three minutes.
However, cold-brew coffee has a distinctively different flavour to espresso – often described as being much more diluted, smooth and mellow – while also containing around one-fifth the caffeine concentration.
The UNSW team continued their work to adjust the ultrasound system to create an espresso-strength shot without the need for hot water.
The process transformed a traditional filter basket into an ultrasonic reactor to brew the grounded coffee beans. The basket generates high-frequency sound waves that help extract flavour, aroma and body from the coffee grounds.
At the heart of the system is a transducer - a small metal device that generates ultrasound while pressing against the side of the coffee basket holding the ground coffee. The ultrasound causes the basket vibrate rapidly, transmitting vibrations through both the coffee grounds and the water.
The ultrasound creates a phenomenon called acoustic cavitation, which is a rapid formation and collapse of microscopic bubbles in the liquid. When these tiny bubbles collapse near the coffee particles, they act like microscopic scrubbing brushes or jets of liquid, pitting and fracturing the coffee grounds and accelerating the bewing process.
This helps break open the surface of the coffee grounds and allows flavour compounds, oils, and caffeine to move into the water much faster than they normally would at such low temperatures.
The result is a concentrated, flavourful shot of coffee comparable to espresso made with traditional machines, but produced using room-temperature water and much less energy.
“We have been working on a range of parameters to discover how to make the perfect ultrasonic espresso,” says Dr Trujillo.
“The most important was the brew ratio – that is how much water is used per gram of coffee – because this helps ensure the final drink is concentrated and not too diluted.
“Another important factor is how finely the coffee beans are ground. We found that by grinding finer we could extract the flavour more rapidly.
“We also experimented with how long the sound waves were applied, as this can affect both the concentration and flavour of the coffee. What we found is that between two-and-a-half and three minutes is a sweet spot for producing a balanced cup.”
To test their results, the researchers also carried out a blind sensory evaluation in which participants did not know which coffee they were drinking.
Four drinks were tested: traditional espresso, ultrasound-brewed espresso, traditional filter coffee, and ultrasound-brewed filter coffee. All coffees were prepared fresh, cooled to the same temperature, served in identical coded cups, and presented in a random order to avoid bias.
Around 100 regular coffee drinkers took part. They were not trained experts, but everyday consumers who drink coffee at least once a week.
Each participant rated the coffees on a simple nine-point scale for aroma, flavour, bitterness and overall liking.
Diagram to show how the ultrasonic espresso system works. Francisco Trujillo/UNSW
The results were striking. For the espresso shots, there were no significant differences between the traditional and ultrasound versions across any of the taste measures. Most participants could not reliably tell them apart, and there was no clear preference for either method.
For filter coffee, however, the ultrasound-brewed version performed even better: participants significantly preferred it overall, particularly rating its bitterness as more pleasant.
“These findings showed that using ultrasound did not harm taste, and in some cases even improved it, despite brewing at room temperature and without the heat normally associated with coffee making,” says Dr Trujillo.
Although the researchers say their new system could be relatively easily developed into an automatic coffee machine for home users, the biggest opportunity is likely to be for large-scale commercial producers of coffee-based drink.
“There are companies that make coffee products on an industrial scale and we are confident this ultrasound system can be scaled up to meet their needs, delivering real benefits in terms of reduced processing times and energy use," says Dr Trujillo.
“The 75% energy saving is particularly beneficial at that scale and we are also able to produce the coffee very quickly.
“Because the process produces a concentrated, espresso-strength coffee, it can be used directly to manufacture ready-to-drink products, or shipped as a concentrate and later diluted into a range of drinks, including cold brew and milk-based coffee drinks.”
Dr Francisco Trujillo preparing ultrasonic coffee. UNSW/Richard Freeman