Spice & Flavor Techniques
Bloom (Coffee)
Also: pre-infusion, coffee bloom, degassing pour
A brief pre-infusion of ground coffee with a small amount of hot water, allowing CO₂ to escape before full extraction begins.
English; coined in specialty-coffee culture in the 2000s; borrowed from the visual metaphor of the coffee bed swelling and 'blooming' like a flower
Definition
When ground coffee is wetted with a small volume of hot water (roughly twice the weight of the coffee) and allowed to rest for 30–45 seconds before the main brew, it blooms: dissolved carbon dioxide accumulated during roasting rapidly escapes as a foam of expanding gases. This degassing step matters because CO₂ is hydrophobic — it repels water and, if not purged first, creates uneven extraction channels and a sour, underextracted result. Fresher-roasted coffees bloom more dramatically and may require a longer rest. The practice applies to pour-over methods (V60, Chemex, Kalita Wave), AeroPress, and batch-brew drip machines; espresso machines handle pre-infusion mechanically. Some roasters consider the visible dome of foam a freshness indicator — stale coffee produces little or no bloom.
In use
“She poured 60 g of water over the 30 g dose, waited for the bloom to subside, then began her slow spiral pour.”
See also
- TechniquePour-Over Brewing
- ConceptExtraction
- IngredientCoffee
Related terms
References
- 1.The World Atlas of Coffee — James Hoffmann (2014)
- 2.Water for Coffee — Maxwell Colonna-Dashwood & Christopher H. Hendon (2015)
- 3.The Coffee Roaster's Companion — Scott Rao (2014)
Confidence: high
Notes
Freshness signal
A vigorous bloom indicates CO₂ still present from roasting — generally a sign of coffee less than four weeks off-roast. Coffee roasted more than six weeks prior produces little foam. This is why specialty roasters stamp roast dates rather than best-by dates.
Optimal water temperature
Most specialty roasters recommend 90–96 °C (195–205 °F) for the bloom pour, matching the full brew temperature, rather than cooler water, which would slow degassing.