Bloom (Pre-Infusion)

The bloom, also called pre-infusion, is the opening step of pour-over and filter brewing: a small volume of hot water — typically 2 times the weight of the dry coffee — is poured over the grounds and allowed to saturate them for 20 to 30 seconds before the main pour begins. During this time, CO₂ trapped inside the roasted beans rapidly degasses, causing the coffee bed to visibly swell and bubble. If this gas is not released before extraction, it repels water, creates uneven flow channels, and results in under-extraction. Fresher roasts bloom more vigorously; very fresh coffee (under 5 days from roast) may require a longer bloom time.

Background & Context

The bloom is the first and most visually dramatic step in pour-over coffee: a small volume of water — typically twice the mass of the dry coffee — poured slowly over the grounds, causing them to swell and release a dramatic dome of CO₂ bubbles. This outgassing is not merely aesthetic; it is chemically significant. Freshly roasted coffee contains CO₂ trapped in the cellular structure of the bean, produced as a byproduct of the Maillard reaction and caramelisation during roasting. If this CO₂ is not allowed to escape before the main extraction begins, it creates a physical barrier between water molecules and coffee solids, disrupting extraction efficiency and producing uneven results. The bloom typically lasts 30–45 seconds for most specialty coffees. Coffees within 7–14 days of roast date bloom most vigorously. Coffee older than 4–6 weeks blooms minimally, signalling degassing completion. In espresso, the equivalent is pre-infusion: a low-pressure soak (1–4 bars) before the full 9-bar extraction begins, allowing the puck to hydrate uniformly. The two-phase approach — bloom then brew — is now standard in all professional filter competitions at WBC and WCE events.

Practical Use

For optimal bloom: use water at 95–97°C poured in a slow, controlled spiral starting from the centre, ensuring all grounds are saturated. Pour 2× the coffee weight (e.g., 30g water for 15g coffee). Wait 30–45 seconds — watch for the dome to collapse and the gurgling to slow. Then proceed with your main pour. If your coffee barely blooms, it is either too old or was stored improperly. Freshness testing via bloom response is one of the most reliable indicators a barista has.

Related Terms

Related terms: Degassing — the physical process the bloom facilitates. Pre-infusion — the espresso equivalent of the bloom. Coffee freshness — bloom vigour directly indicates freshness. V60 — the filter method most associated with bloom technique.