Bloom (espresso)

The initial swelling and off-gassing of the puck during pre-infusion as trapped CO₂ escapes from fresh coffee. Visible as a puffing or rising of the puck before the shot starts to flow.

Why it matters — Very fresh coffee (under 7 days off roast) blooms aggressively, which can disrupt puck integrity and cause channelling. Letting beans rest 10–21 days lets them bloom in a more controlled way.

Good to know

• A long pre-infusion (8–15 seconds) lets the bloom complete before full pressure ramps in, which helps with very fresh or very lightly roasted coffees.
• If you can hear a faint hissing or see steam during pre-infusion, that's the bloom releasing CO₂.