Bloom releases the coffee's gas.
Freshly roasted coffee holds CO₂. Wetting the grounds first lets that gas escape, so the following pours extract evenly.
What it is
The first, small pour: about two to three times the coffee's weight in water, followed by a short wait.
Why it matters
Freshly roasted coffee holds carbon dioxide. When hot water arrives, the gas escapes and pushes the water away. Letting it out first means the following pours extract evenly.
In practice
Pour 2–3× the coffee's weight, make sure every bit is wet — a gentle swirl helps — and wait 30–45 seconds. Fresh coffee rises like a dome; old coffee barely moves.