The Role and Characteristics of Espresso Pre-infusion: Is Blooming Necessary for Making Espresso?

In pour-over coffee, blooming is an extremely important process. It's no exaggeration to say that if the blooming step is eliminated, it would introduce many uncertainties to pour-over coffee, potentially resulting in a final brew whose flavor profile even the brewer couldn't predict.

Some friends might wonder: since blooming has such a significant impact on the final flavor presentation of pour-over coffee, does espresso also require blooming?

Actually, espresso doesn't include a blooming step. When extracting coffee using an espresso machine, the coffee grounds are compressed into a compact puck, and then rich coffee liquid is "pressed" out under 9 bar water pressure. This is why espresso is known for its stable extraction. For example, the classic espresso extraction recipes we've heard about in the past involve extracting 1 ounce of coffee liquid within 20-30 seconds. Theoretically, as long as these three parameters—dose, yield, and time—remain stable, the flavor of espresso can be consistently produced.

However, with the increasing variety of roast levels applied to espresso beans and the pursuit of coffee bean freshness, espresso extraction is no longer as stable as it once was.

For instance, espresso beans used in the past had a resting period of as little as half a month or as long as one month. Most of the active gases within the coffee beans had been released, meaning the state changes in properly rested beans were not significant, resulting in very consistent extraction performance.

Nowadays, to emphasize freshness, the resting period has been shortened. It's possible that during extraction, the beans still contain abundant carbon dioxide, which results in coarser crema and unstable extraction.

The Rise of Pre-infusion in Espresso Extraction

Therefore, adding a "pre-infusion" stage during espresso extraction has become increasingly popular.

Pre-infusion extraction involves starting with unpressurized water flow after locking in the portafilter, moistening the coffee puck, waiting for a period of time, and then beginning the actual pressurized extraction. This can be understood as the "blooming" of espresso.

The effects of pre-infusion are quite apparent. The first benefit is the release of active gases. Just as with coffee beans that haven't been properly rested, overly active carbon dioxide can affect extraction stability. Therefore, performing pre-infusion before the actual extraction releases this carbon dioxide first, preventing it from interfering with subsequent extraction.

Benefits of Pre-infusion

The second benefit is reducing the likelihood of channeling. The 9 bar water pressure is extremely strong. If the coffee puck isn't evenly distributed and tamped, water columns can easily break through weaker areas, creating channeling. By first going through the pre-infusion stage, the coffee puck absorbs water and expands, making it more compact and thus reducing the occurrence of channeling.

The third benefit is that the application of pre-infusion makes espresso extraction recipes less monolithic. For example, when dealing with sharp acidity during extraction in the past, the only adjustment options were changing the grind size or adjusting the ratio. Now, pre-infusion can also be used to improve subsequent extraction efficiency.

How to Implement Pre-infusion

The prerequisite for using pre-infusion is that the coffee machine itself supports this function. Some machines allow setting one-touch pre-infusion extraction, while others require manual pre-infusion. If you're in a manual situation, you can determine when to stop the water flow by observing the first drops. For instance, FrontStreet Coffee observes through a bottomless portafilter—coffee liquid typically starts to seep from the bottom between 3-4 seconds, so you can stop the water flow at the 3-second mark to begin pre-infusion.

As for how long to pre-infuse before starting the actual extraction, there's no standard answer to this question. You might pre-infuse for 5 seconds, or 10 seconds, or even 30 seconds. This depends on the resting state of the coffee beans and how it harmonizes with parameters like grind size and ratio to achieve the desired flavor profile.

Important Notice :

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