Pre-infusion is a "preparatory" stage in coffee preparation. If the coffee is fresh, pre-infusion helps to degas it beforehand, stabilizing the extraction and enhancing the flavor. In this article, we will explain the purpose of pre-infusion.
Pre-infusion, also known as blooming, refers to the rapid release of carbon dioxide gas that occurs when hot water comes into contact with ground coffee.
What is Pre-infusion?
Pre-infusion is a brewing stage that precedes the pouring of the main volume of water. To perform pre-infusion, a small amount of water is poured over the ground coffee and allowed to saturate it for a certain period.
The volume of water for pre-infusion is calculated based on a ratio of 2-3 grams of water per 1 gram of coffee. For example, for a 15-gram portion of coffee, you would need 30 grams of water for pre-infusion. Typically, pre-infusion lasts for 30-40 seconds. When this time elapses, the main brewing stage begins, which involves pouring the water.
According to Maxwell Colonna-Dashwood, the author of the book "The Coffee Dictionary," pre-infusion allows for the assessment of roast freshness rather than brewing quality. James Hoffmann, the author of the book "The World Atlas of Coffee," notes that there is no scientific evidence proving the necessity of pre-infusion. However, some studies still suggest that pre-infusion promotes the release of carbon dioxide gas and helps to brew coffee better.
During the soaking process, the ground coffee expands in volume. This facilitates the access to soluble compounds, and coffee oils come to the surface. Pre-infusion helps to stabilize the brewing process and improves the quality of extraction.
The Purpose of Pre-infusion
Pre-infusion is typically performed during the preparation of freshly roasted coffee to artificially enhance the degassing process, make the brewing process more manageable, and improve the taste of the coffee.
During the first 2-3 weeks after roasting, coffee releases carbon dioxide gas actively. When we grind the coffee beans, the rate of gas release increases significantly due to the increased surface area of the coffee. Then, when we pour hot water, the rate of gas release further accelerates.
Pre-infusion is necessary to allow most of the gas to escape before the main brewing stage begins:
If carbon dioxide gas remains in the coffee beans and participates in the extraction process, it forms carbonic acid when it comes into contact with water. This makes the coffee excessively acidic. Removing excess carbon dioxide gas allows for a more flavorful cup of coffee.
The escaping carbon dioxide gas "pushes away" the water and hinders the brewing process. The water can only freely extract aromatic compounds and oils from the coffee after the carbon dioxide gas has escaped. However, if the gas escapes too quickly from the coffee, it hampers the water's ability to evenly contact the ground coffee, resulting in uneven extraction. To avoid this, pre-infusion is necessary.
The process of pre-infusion is influenced by water temperature, humidity, roast level, coffee bean hardness, and origin.
If the ground coffee doesn't bubble during pre-infusion, it is likely that the gas has already escaped from the beans. This typically occurs for two reasons: stale coffee or improper packaging where the coffee has been exposed to oxygen for an extended period.
Pre-infusion in the Espresso Brewing Process
Modern coffee machines are equipped with a pre-infusion function that can be turned on or off as desired. The essence of the process remains the same—to ensure the coffee puck is saturated and the extraction begins.
During pre-infusion, hot water saturates the coffee puck and allows it to slightly swell. This prevents channeling and over-extraction in specific areas, improving the taste of the cup, although it slightly complicates the espresso setup process.
It is important to understand how pre-infusion affects the taste of coffee in different conditions. We always recommend using pre-infusion if the coffee was roasted less than a week ago. In other cases, whether to use pre-infusion or not is a personal choice.