Scientists have figured out how to make espresso without boiling water

The new method uses ultrasound – sound waves of such a high frequency that humans cannot hear them. They help to ‘extract’ the flavour, aroma, oils and caffeine from ground coffee more quickly, even at room temperature.

The researchers claim that this method can reduce energy consumption by around 75%, as there is no need to heat the water. The technology may be particularly useful not so much for home kitchens as for factories that produce ready-made coffee drinks, concentrates and cold brew.

Details

A standard espresso is made as follows: hot water under pressure is forced through finely ground coffee. In a short time, the water extracts aromatic compounds, oils and caffeine from the beans. This results in a dense, rich and strong drink.

In the new method, hot water has been replaced with water at room temperature, and ultrasound has taken over part of the process.

Scientists have turned a standard coffee basket into a small ultrasonic reactor. The system contains a metal component — a transducer — which generates high-frequency vibrations. These vibrations pass through the water and the ground coffee.

The main effect is called acoustic cavitation. Put simply, tiny bubbles appear in the water, which quickly collapse. When this happens near the coffee particles, they act like microscopic jets and ‘brushes’: they damage the surface of the coffee particles and help the water extract the desired substances more quickly.

This is precisely why the coffee brews faster, even though the water isn’t hot. According to the researchers, the optimal time for this method turned out to be around 2.5–3 minutes.

The team also tested various parameters: how much water to use per gram of coffee, how fine the grind should be, and how long to apply the ultrasound. It turned out that a fine grind helps to achieve a rich flavour more quickly, and the correct ratio of water to coffee prevents the drink from becoming too watery.

Separately, the scientists conducted a blind taste test. Around 100 ordinary coffee lovers tasted different drinks: traditional espresso, ultrasonic espresso, regular filter coffee and filter coffee prepared using ultrasound. The participants did not know which drink they were being given.

According to the test results, no significant differences were found between the regular espresso and the ultrasonic version in terms of aroma, taste, bitterness and overall rating. In other words, most participants were unable to reliably distinguish one drink from the other.

With filter coffee, the result was even more interesting: participants preferred the ultrasonic version, particularly in terms of bitterness.

Why this matters

The main practical benefit is energy savings. In the coffee industry, huge volumes of water are heated every day. If some drinks can be prepared without heating, this will reduce costs and the strain on production.

For the average person, the idea also sounds appealing: strong coffee without boiling water, ready in a few minutes and without any loss of flavour. But for now, the technology is more important for industrial applications — for example, for ready-made coffee drinks in bottles and tins.

Another advantage is speed. Classic cold brew usually steeps for 12–24 hours. Ultrasound had previously made it possible to speed up this process to a few minutes. Now researchers have shown that it is possible to produce not just a mild cold coffee, but a drink with a strength similar to that of an espresso.

But the findings should not be overstated. This is not ‘magic coffee’ nor a definitive replacement for a barista. The taste depends on the beans, the grind, the recipe, the equipment and the serving temperature. The new method shows that ultrasound could become a significant tool in coffee technology, but it still has some way to go before reaching the mass market.

Background

Ultrasound has long been used in the food industry. It helps to accelerate extraction — that is, the removal of the desired substances from raw materials. In the case of coffee, these are aromatic compounds, oils, acids, caffeine and other substances on which the taste of the drink depends.

Interest in such methods is growing for two reasons. The first is energy savings. Heating water requires resources, especially in large-scale production. The second is the demand for ready-to-drink coffee beverages: cold coffee, coffee concentrates, drinks with milk and ready-to-drink products.

The new study shows that ultrasound can not only speed up cold brewing but also create a drink with a richness close to that of espresso. This makes the technology significantly more appealing for businesses and for future coffee machines.

Source

Study: Nikunj Naliyadhara et al., ‘Ultrasound enables espresso-strength coffee brewing in 2–3 minutes at low temperature with lower energy consumption’, Journal of Food Engineering, 2027.