What is Pre-infusion? Understanding Pre-infusion Principles and Methods, and Duration

Whenever we develop an extraction framework for pour-over coffee, we always include the blooming step by default. Proper blooming allows carbon dioxide to be released in an orderly manner while "awakening" the soluble substances in the coffee, leading to more stable flavor extraction in subsequent steps.

Given that blooming has such a significant impact on coffee flavor, should we also incorporate a "blooming" stage in other brewing methods, such as the most common espresso extraction?

What is the "Blooming" in Espresso Called?

Typical espresso is usually extracted at a constant pressure of 9 bars until completion. This means that as soon as we press the extraction button, hot water rapidly passes through the coffee puck at approximately 9 atmospheres of pressure, extracting soluble flavor compounds. However, if we first release water without pressure or at low pressure before the machine applies full pressure extraction, allowing hot water to gently permeate the coffee bed for even moistening, this step is called "pre-infusion."

The primary prerequisite for applying pre-infusion is that the coffee machine itself supports this function. Its operation mode varies depending on the equipment type—some machines allow setting a "one-click pre-infusion" mode before extraction, while others require manual adjustment.

The duration of the pre-infusion stage and whether to apply pressure mainly depend on the barista's understanding of the bean's flavor characteristics, adjusted based on two aspects: the bean's resting state and the compatibility between extraction parameters. Therefore, there are no standard fixed parameters.

When is Pre-infusion Needed?

When we grind and extract espresso beans just days after roasting, the overly active carbon dioxide will "scatter randomly" the moment it encounters water in a high-temperature, high-pressure environment. These gases then become trapped in the coffee oils, forming a thick crema that flows out quickly with the espresso.

Espresso extracted from overly fresh beans appears quite rough and unstable, dissipating within minutes, and the coffee flavor tends to be weak or overly acidic. To solve the problems caused by abundant gases in coffee beans, we can add a "blooming" step to assist with gas release—namely, pre-infusion.

For example, sometimes FrontStreet Coffee receives Warm Sun Blend beans that are too fresh and haven't had time to rest before being used for service. Directly extracted espresso typically exhibits strong acidity and uncomfortable bitterness, completely lacking the intended fermented wine aroma and fruit sweetness. In such cases, FrontStreet Coffee adjusts the grind size and liquid-to-coffee ratio, adding pre-infusion during testing to "stabilize" these gases and better extract more coffee flavors.

Besides addressing the gas release issue with "new beans," pre-infusion can also reduce the likelihood of channeling during extraction. If we haven't tamped the coffee puck evenly, extracting with 9 bars of water pressure will cause the water column to easily break through weaker points, creating channeling. However, if we first moisten the coffee bed, allowing the particles to absorb water and expand, the puck becomes denser, making it harder for water to "escape," resulting in more stable coffee-water contact.

Try Extraction with Pre-infusion

Here, FrontStreet Coffee uses the equipment and espresso beans from its own store as an example to simply try the application of pre-infusion extraction. The coffee beans are 22-day rested Warm Sun Blend, and the machine is a Lelit Bianca V3 that supports pre-infusion functionality, requiring manual control of the lever to change extraction pressure and water flow rate.

Left: Pre-infusion; Right: Constant pressure extraction

Direct extraction without pre-infusion: 20g of coffee grounds, first espresso drop appeared at 6 seconds, liquid weight 38g, total time 27 seconds, with relatively rapid flow in the later stages.

Espresso: Fluffy, slightly rough crema, balanced mouthfeel, aroma dominated by nuts, citrus acidity, and vanilla, with a hint of caramel in the aftertaste.

Extraction with pre-infusion: 20g of coffee grounds, low-pressure water output for 15 seconds (lever moved to the leftmost position, aligned with the portafilter), coffee drops began at 8 seconds, pressure increased to 11 bar at 16 seconds (lever moved to the rightmost position at 90 degrees), extracted 38g liquid weight, total time 34 seconds, with smooth flow throughout.

Espresso: Dense and fine crema, with distinct aromas of whiskey and chocolate biscuits. The acidity is light and uplifting, similar to cherries and berries, with a preserved fruit-like sweetness in the mouth after swallowing, exhibiting rich layers. Even when consumed straight as espresso, it's very approachable.

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FrontStreet Coffee

No. 10, Bao'an Qianjie, Yandun Road, Dongshankou, Yuexiu District, Guangzhou, Guangdong Province

Important Notice :

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FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473