A technique that over the last four years has grown from a competition trick into a bar surprise around the world. The principle is simple, the result is unexpected — espresso is extracted over a frozen metal ball, which instantly chills the liquid as it leaves the portafilter. What you get in the cup isn’t a “colder espresso,” but a different espresso.
Where it came from
The technique known as extract chilling was first used at the World Barista Championship (WBC) by Berg Wu from Taiwan in 2016, who cooled the portafilter with ice before extraction. Five years later, at WBC 2021, Australian Hugh Kelly took the method to a new level — using a frozen metal block attached to the side of the cup, over which the first 12 grams of espresso flowed. Behind this move stood research from the Swiss institute ZHAW, where Prof. Chahan Yeretzian documented that fast cooling of the extract retains more volatile aromatic compounds.
What actually happens
During a standard extraction, the coffee comes out at around 75–85°C. At that temperature, volatile aromatic compounds — the molecules responsible for smell and aromatic complexity — evaporate very quickly. In other words, most of what makes specialty coffee specialty ends up in the air before it reaches the palate.
By cooling the first 30–40% of the extract — the portion richest in volatiles — those molecules are “locked” in the liquid. ZHAW research shows the method can preserve on average up to 10% more volatile compounds, and in individual cases up to 40%.
What it does in the cup
The difference is noticeable even when the coffee is drunk hot. The aroma is more intense and clearer — fruity, floral and citrus notes that usually get “lost” in hot espresso now stay present. The texture is denser and more creamy. The bitterness from the final seconds of extraction is softened. The finish is longer, with a more pronounced aftertaste.
The effect is particularly strong on lighter-roasted coffees with accented aromatic profiles — Ethiopia, Kenya, Geisha varieties. On darker roasts the difference is smaller because the volatiles have already been partially degraded during roasting.
How to do it at home
Commercial balls are on sale (Coffee Alive Extract Chilling Ball, Nucleus Paragon Espresso Rock, MHW-3BOMBER, NEOUZA), most often stainless steel, 30–50mm in diameter. The ball is frozen overnight (ideally at -15°C or below), then placed under the portafilter so the first part of the espresso falls directly onto it. After the first 30–40% of extraction, the ball is moved aside and the rest of the extraction continues normally.
An alternative for experimenting without buying a special tool is a frozen stainless steel spoon or a whiskey stone — the effect is weaker because it melts faster, but it gives a basic idea of what the technique does.
Does it make sense?
This is a technique that genuinely changes the cup profile, but its effect is subtle and demands a careful palate to notice. For a light-roasted coffee with a complex aromatic profile — worth trying. For a standard espresso blend or darker roast — the effect is marginal and may not justify the extra workflow step.