The Coffee Bloom: Why Your Pour Over Bubbles (And Why It Matters)

The first time I did a proper pour over, I watched the coffee bed bubble and rise like a tiny science experiment and thought something was wrong. Turns out, that dramatic puffing is one of the best things that can happen during brewing. It is called the bloom, and it is your coffee telling you it is fresh.

What Is Happening

When coffee is roasted, CO2 gas gets trapped inside the bean structure. Fresh beans can contain up to 10 milliliters of CO2 per gram. When hot water hits the grounds, that gas releases rapidly, creating the bubbling and expansion you see during the bloom phase. This is a simple degassing reaction and it directly affects how well your coffee extracts.

How to Bloom Correctly

Pour twice the weight of your coffee dose in water (so 36 grams of water for 18 grams of coffee) in a gentle spiral. Make sure all the grounds are saturated. Wait 30 to 45 seconds. You will see the bed rise, bubble, and then start to fall as the gas escapes. Once the bubbling subsides and the bed begins to flatten, start your main pour.

One thing worth noting: very fresh beans (less than 3 to 4 days off roast) can bloom so aggressively that they interfere with brewing. The excessive CO2 makes it hard to get an even extraction. This is why most roasters recommend resting beans for 5 to 14 days before brewing. Fresh is good. Too fresh can actually be problematic. Let your beans breathe, then bloom them properly, and you will taste the difference.