Updated October 2026 · Filter Recipe Series
When hot water first hits fresh coffee, the grounds swell, dome up and bubble. That's the bloom: carbon dioxide from roasting escaping from the coffee. Most people rush it. In the Filter Recipe Series every recipe gives it 60 seconds, because the bloom is doing far more than letting gas out.
Pour about three times the dose in water, stir so every ground is wet, then wait the full 60 seconds. Fresh, well-stored beans hold a lot of CO₂, and much of the extraction happens during the bloom, so don't rush it. If the coffee degasses again when you start the main pour, the bloom was too short.
What is bloom?
Roasting creates gases, mostly carbon dioxide. Part escapes during roasting; the rest stays trapped in the bean's porous structure and is released slowly in storage, and much faster when you grind and brew.
Escaping gas pushes water away from the grounds, so water can't get in to dissolve the flavours. Give it time to get out of the way and every particle can extract evenly.
Freshness
If your beans have been stored correctly, they'll be much fresher and hold far more CO₂. That's good news for flavour, but it means they need a proper bloom to get the gas out of the way.
Degassing is fastest in roughly the first three weeks after roasting, then slows dramatically. Fresh beans still hold plenty of CO₂, so they dome up and bubble.
Once most of the CO₂ has gone, the grounds barely rise. Little or no bloom is a sign the beans are past their best.
Heat, oxygen, humidity, light and time all speed up staling. Keep whole beans airtight, cool and dark, and grind just before brewing: grinding releases CO₂ dramatically. See how to store coffee beans.
Extraction
It's tempting to think of the bloom as preparation before the real brewing starts. It isn't.
Measuring a pour-over in stages, Royal Coffee found a remarkable amount of extraction happened in the first 30 seconds, during the bloom alone.
The Zurich University of Applied Sciences found the first 10% of a filter extraction is around 2–3 times the concentration of the finished cup. Fresh water meeting fresh coffee picks up solubles fastest.
Fruit acids and the most soluble compounds dissolve first, so the bloom sets up much of the brightness and sweetness of the cup.
Just like pre-infusion in espresso, the bloom is a key part of the brew. Rushing it means rushing the part of the brew that matters most.
How to bloom
Pour straight from the kettle, without a Melodrip, about three times the dose in water.
Stir with a wet WDT stick so every ground is wet and no dry clumps are left. Dry pockets can't degas or extract.
Wait the full bloom time on your recipe. Don't cut it short: the gas needs time to get out.
Then carry on with the main pour, in small batches through a Melodrip, keeping the water just above the coffee bed. If the bed bubbles up again as you start, that's a second degas: bloom longer next time.
Most guides say 30 seconds, and most people don't even wait that long. Here's how to tell: when you start the main pour after the bloom, watch the bed. If it bubbles up again in a second degas, there was still CO₂ in the coffee and the bloom wasn't long enough. Next time, give it longer. You are not in a hurry.
References
Keep reading
Find your starting recipe, then dig deeper into what drives extraction.
Find your recipeKeep your beans fresh and full of CO₂, including freezing single doses.
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