What is the Main Reason and Purpose of Coffee Blooming? How is Espresso "Blooming" Done?

The bloom during pour-over brewing is an important step used to release carbon dioxide from the coffee grounds, allowing subsequent water pouring to better extract aromatic compounds. If this step is eliminated, it will introduce many unstable factors to the subsequent extraction.

Espresso extraction, by contrast, is much more "forceful" - directly using high-pressure hot water to "press out" aromatic compounds from the coffee grounds, with no "blooming" process during this extraction period. This has led some friends to wonder: if espresso extraction also incorporated blooming, what changes would it bring to the final coffee? In fact, adding "blooming" to espresso extraction has been practiced by some people for quite some time and has become part of the daily extraction routine in certain coffee shops. This technique is what we commonly refer to as "pre-infusion."

What is Pre-infusion?

Typically, when making espresso, we use the factory default pressure of an espresso machine - "9 bar" - for continuous extraction throughout the entire process. Pre-infusion refers to using lower pressure to allow water to penetrate the coffee puck before using full pressure (9 bar or above) for extraction, then stopping the water flow for a period to let it soak, before resuming the extraction process. This action is called pre-infusion, meaning to soak in advance of extraction.

Its purpose is to allow the coffee grounds to achieve degassing through pre-soaking (consistent with the principle of pour-over blooming)! So, for espresso extraction, what impact does adding this degassing step have on the subsequent extraction?

Benefits of Pre-infusion

The first benefit of pre-infusion is its ability to increase extraction yield! When the coffee puck is pre-degassed, subsequent full-pressure (9 bar) extraction will more easily obtain soluble compounds! This is especially true for fresh coffee beans, which contain large amounts of gas and are ideal candidates for pre-infusion. When using fresh coffee beans, the abundant carbon dioxide they contain not only results in coarse crema but also makes it difficult for hot water to extract aromatic compounds, easily leading to a series of negative experiences such as under-extraction and rough mouthfeel.

This is where pre-infusion can effectively improve these issues. When this carbon dioxide, which hinders extraction, is released, we can more easily extract the aromatic compounds from the coffee - this is what we commonly call increasing extraction yield! Issues like coarse crema are naturally improved as well. Additionally, it can reduce channeling, which is its second benefit! Since conventional extraction uses 9 bar of high pressure throughout, which is quite forceful, if we don't achieve even distribution when dosing and tamping, it will cause hot water to break through those weaker, less-dense areas under strong pressure during extraction, thus creating channeling.

Channeling leads to severely uneven extraction, and pre-infusion can effectively solve this problem! When we use pre-infusion, the coffee grounds will first expand under the soaking of a small amount of hot water, allowing the puck to become more compact and less prone to perforation. Therefore, we can conclude that increasing extraction yield and improving extraction are the unique advantages of pre-infusion. However, to harness these advantages, there are prerequisites - it must be used properly! Most machines don't have a one-touch pre-infusion extraction function, so we can only use manual control for pre-infusion!

How to Properly Use Pre-infusion

During pre-infusion water pouring, we can choose to inject it at low pressure or no pressure, because using 9 bar pressure directly for pre-infusion反而更容易因为冲破了咖啡表面的粉层而出现通道效应；

Then, the soaking time only needs to be set according to the freshness of the beans. The fresher the beans, the longer the soaking time should be, as sufficient time is needed to allow them to release ample carbon dioxide. A range of 5-10 seconds is acceptable. For beans that aren't as fresh or well-cured dark roast beans, pre-infusion isn't necessary because they extract well on their own!

- END -

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

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473