What is bloom, and why do you bloom coffee?
is the 30-45 second pause at the start of pour-over where you wet the grounds with a little hot water and they swell and bubble as trapped gas (CO₂) escapes. It's how you let fresh coffee 'de-gas' so water can extract evenly.
Sources show where the underlying information came from. They do not automatically make a claim correct, so disputed history, evolving science and uncertain claims should be labeled as such in the explanation itself.
Freshly roasted coffee traps carbon dioxide inside the bean. When hot water first hits it, that CO₂ rushes out — you see the bed bubble and rise. The problem: escaping gas physically pushes water away from the grounds. Brew through it and you get channeling — some grounds extract fully, others barely at all, and the cup turns uneven. So pour roughly twice the coffee's weight in water (e.g. 60g water for 30g grounds), wait 30-45 seconds until the bubbling settles, then continue your pours. The is also a freshness check: very fresh coffee blooms dramatically; months-old coffee barely bubbles — a sign its aromatics have already faded. In espresso the same gas is why fresh shots creep rather than flow.
- ·Specialty Coffee Association brewing standards(No direct source link provided)