A research team led by the University of New South Wales has shown espresso-strength can be brewed at a low temperature in minutes.
Traditional espresso preparation relies on elevated temperature (90–95 ◦C) and high hydraulic pressure (≈9 bar) to force water through a tightly packed bed of finely ground coffee.
Tamping, the act of compressing the coffee grounds at the bottom of the filter basket, is essential for forming a dense granular bed with high resistance to flow, necessitating substantial pressure for water to permeate the puck.
This allows for the rapid extraction of soluble compounds, emulsified lipids, and volatile aromatics, producing a dense and aromatic beverage.
But extraction outcomes depend strongly on operator-controlled variables such as tamping force, flow rate or time, dry coffee mass (dose), and grind setting. The process is recognised as a complex and sensitive operation, and as a result, the product can vary in quality.
Using a patented ultrasonic brewing sonoreactor, the research team were able to brew the beverage in 2-3 minutes, dramatically reducing production time, removing the need for high temperatures and reducing the reliance of traditionally pressure-driven extraction.
In tests, the team were able to do this without significantly altering the aroma or physicochemical markers (e.g. colour, pH, caffeine, chlorogenic acid concentration).
The new technique allowed for more solids to be extracted per gram of coffee and better control over strength and flavour, at the same time as offering sustainability gains.
Compared to conventional espresso machines, the ultrasonic coffee saw a 75% reduction in energy consumption, potentially opening up opportunities for cost savings and low energy production in the future.
According to the team, under identical conditions without ultrasound, espresso-strength extraction was not possible.
The same platform can also be used to produce both concentrated and filter-style coffees; and can reduce cold brew production times from hours to minutes.
The full study Ultrasound enables espresso-strength coffee brewing in 2–3 minutes at low temperature with lower energy consumption has been published in the Journal of Food Engineering.
