The bloom is the first small pour in a filter brew, followed by a pause of thirty to forty-five seconds before you carry on.
What is happening
Roasted coffee holds carbon dioxide, and grinding releases it. When hot water hits fresh grounds, that gas escapes rapidly — you can see the bed swell and bubble.
CO₂ repels water. While it is escaping, water cannot penetrate the grounds evenly, so extraction is patchy and the brew channels.
Giving it thirty to forty-five seconds lets most of the gas out before the real brewing starts.
How to do it
Pour roughly twice to three times the coffee weight in water — 30 to 45 g (1.1 to 1.6 oz) for a 15 g (0.5 oz) dose. Wet everything; a gentle swirl helps more than careful pouring. Then wait.
When it matters and when it does not
Fresh coffee, under three weeks old: the bloom is doing real work and skipping it is visible in the cup.
Coffee over two months old: there is little gas left. You will see almost no swelling, and the bloom achieves little.
That is the counter-intuitive part — the fresher your coffee, the more you need the step.
Espresso
The equivalent is pre-infusion: a low-pressure phase before full pressure, wetting the puck so nine bars meets a saturated bed rather than dry coffee.
What people want to know
How long should the bloom be?
Thirty to forty-five seconds for most coffee. Very fresh beans benefit from the longer end. Past about a minute you are simply extracting slowly at low temperature.
Last reviewed 30 October 2026