Bloom Time Explained
Why the first 30 seconds matter most in your brew.
The bloom phase is the foundation of a great pour-over coffee. These critical first 30-45 seconds set the stage for everything that follows, and understanding the bloom can dramatically improve your coffee.
What is the Bloom?
When hot water first contacts freshly ground coffee, it causes trapped CO2 gas to rapidly escape. This creates the characteristic bubbling and expansion you see at the start of brewing. This is the bloom.
Coffee releases CO2 for several days after roasting. Fresher coffee blooms more dramatically because it contains more trapped gas. This is why you'll see a vigorous bloom with coffee roasted 3-14 days ago, but little to no bloom with coffee roasted months ago.
Why Blooming Matters
If you don't allow coffee to bloom properly, CO2 can interfere with extraction in two ways:
- CO2 creates pressure that prevents water from fully saturating coffee particles
- The gas creates channels in the coffee bed, leading to uneven extraction
The Perfect Bloom Technique
Start by pouring 2-3 times the weight of your coffee grounds in water. For example, if you're brewing 20g of coffee, pour 40-60g of water during the bloom.
Pour gently in a spiral pattern, ensuring all grounds are evenly saturated. Then wait 30-45 seconds before continuing your pour. You should see vigorous bubbling and expansion during this time.
Bloom as a Freshness Indicator
The vigor of your bloom is a reliable indicator of coffee freshness. A dramatic, vigorous bloom indicates fresh coffee with plenty of retained gases and aromatic compounds.
If you see little to no bloom, your coffee may be stale. While you can still brew it, the flavors will be muted compared to fresher coffee. This is why buying from roasters who date their bags is so important.