In coffee brewing, what does the term “bloom” refer to?

The term "bloom" in coffee brewing refers to the initial release of gases from coffee grounds when hot water is added. This gas, primarily carbon dioxide, is a byproduct of the roasting process and is present in the coffee grounds. When brewing begins, especially in methods like pour-over or French press, the hot water causes these gases to escape, allowing for more effective extraction of flavors during the brewing process. The bloom phase typically lasts for about 30 seconds and can enhance the resulting coffee’s aroma and body.

The importance of this step cannot be overstated; it prepares the coffee grounds for optimal extraction by improving water contact and reducing channeling, which can lead to uneven brewing. Understanding bloom helps baristas make informed decisions about brew time and water temperature for the best flavor profile in each cup.