Brewing Methods
Coffee Bloom Explained: CO2 Release During Brewing
Also known as: coffee bloom, degassing, blooming
The bloom is the rapid release of carbon dioxide gas from freshly ground coffee when it first contacts hot water. This degassing causes the coffee bed to swell and bubble, and is most visible during the first 30 to 45 seconds of a pour over brew.
The bloom is the rapid release of carbon dioxide gas from freshly ground coffee when it first contacts hot water. This degassing causes the coffee bed to swell and bubble, and is most visible during the first 30 to 45 seconds of a pour over brew.
This concept is explored in depth in The Complete World of Coffee. Read a free sample chapter.
Definition
The bloom is the rapid release of carbon dioxide gas from freshly ground coffee when it first contacts hot water. This degassing causes the coffee bed to swell and bubble, and is most visible during the first 30 to 45 seconds of a pour over brew.
Why It Matters
The bloom is an indicator of coffee freshness. Freshly roasted coffee contains trapped CO2 from the roasting process, and a vigorous bloom signals that the coffee was roasted recently. Allowing the bloom to settle before the main pour prevents channeling and promotes even extraction. A weak or absent bloom may indicate stale coffee.
Related Articles
Related Brewing Methods
Book References
- Chapter 3: Core Brewing Variables
- Chapter 4: Roasting and Freshness
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Editorial Standards & Trust
Keith E. Lyons
Author, Researcher & Coffee Educator
Keith E. Lyons is the author of The Complete World of Coffee and the publisher behind Lyons Den Publishing. A licensed trauma therapist turned specialty coffee writer, Keith blends scientific rigor with genuine passion for the craft of coffee.
Last Reviewed
July 22, 2026
Sources & References
(6)Claims are cited to verifiable sources. Peer-reviewed research is marked.
- 1Lyons, K.E. The Complete World of Coffee. Lyons Den Publishing. 2024.
- 2Specialty Coffee Association. SCA Cupping Protocols and Scoring Standards. 2022. https://sca.coffee/research/protocols-best-practices
- 3Wang, X., et al. Carbon Dioxide Degassing from Freshly Roasted Coffee Beans. Journal of Agricultural and Food Chemistry. 2021. https://pubs.acs.org/journal/jafcau
- 4Clarke, R.J. and Macrae, R. Coffee: Chemistry. Volume 1. Elsevier Applied Science. 1985.
- 5Illy, A. and Viani, R. Espresso Coffee: The Science of Quality. 2nd ed. Academic Press. 2005.
- 6Sunarharum, W.B., et al. Complexities of Gas Release and Solvent Extraction in Coffee Brewing. Comprehensive Reviews in Food Science and Food Safety. 2020. https://ift.onlinelibrary.wiley.com/journal/15414337
Authoritative References
Editorial Standards
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