What is a Coffee Bloom?

Key takeaways

A coffee bloom is the visible bubbling and expansion of freshly ground coffee when it comes into contact with hot water, caused by the rapid release of carbon dioxide
Blooming allows water to properly saturate the coffee grounds, preventing under-extraction and ensuring a rich, balanced, and fully flavorful cup
The presence and size of a coffee bloom act as a visual indicator of bean freshness

You keep hearing about it, but you might still be wondering exactly what a coffee bloom is and why it matters. We’re here to help clarify the science behind the brew. The next time your know-it-all coffee friend goes off on a blooming spiel, you’ll have the knowledge to join the conversation and brew an incredibly delicious cup yourself. Let's dive in!

Coffee Blooms Explained

A coffee bloom is the bubbling "bloom" you see when those first drops of water hit your coffee grinds.

When coffee beans are roasted, their organic material is heated, creating and trapping carbon dioxide. Beans will naturally release these gases, or “degas,” gradually over about 14 days (with most of the gas releasing in the first 10 days). When you grind your coffee, you speed up the degassing process, which is exactly why you should always grind it right before you brew.

Hot water acts as a catalyst, causing the beans to immediately release most of the carbon dioxide they have trapped. This rapid release creates the beautiful, bubbling "bloom."

Why does a good coffee bloom matter?

Coffee drinkers who have never bloomed can miss out on some of the best flavors in their coffee, and also introduce some new, unwanted ones. When you first pour hot water over the coffee grounds, the release of carbon dioxide can push the water out of the way rather than allowing it to soak into the grounds, a process known as turbulence. This is in issue because it interferes with the water and coffee interaction, leading to under-extraction and preventing the coffee’s delicious natural flavors and textures from fully releasing into your cup.

Additionally, if you pour too much water at once, the carbon dioxide in the coffee may negatively affect the final flavor and lead to acidic or sour tasting coffee. Carbon dioxide does not taste good! Blooming your coffee first allows the carbon dioxide to release before you begin brewing and leads to a well-balanced, better extracted, and more flavorful cup.

How to get a good coffee bloom

Learning how to bloom coffee is easy and adds less than a minute to your morning routine.

Start the pour: Begin pouring your hot water at the center of your coffee bed, slowly working your way out to the sides.
Measure the water: Pour roughly twice as much water as the coffee you are using. The grounds should be uniformly soaked, but not dripping wet.
Wait and watch: Pause your pour and wait 30 to 45 seconds for the coffee to “bloom” and release its CO2.

Need to see it to believe it? Here’s a handy video from Coffee Experimental for a visual aid:

Pour-Over Bloom

For pour-over coffee, blooming is an essential step in crafting a high-quality cup. Because you have complete control over the pouring process, you can ensure that all the grounds are fully and evenly covered. This allows for a consistent degassing rate and guarantees a smooth, balanced flavor profile.

There are a few things you can do to ensure that your pour-over coffee blooms:

Use freshly roasted coffee beans
Grind your coffee just before you brew it
Store your coffee in an airtight container, preferably in the freezer

French Press Bloom

You won’t see it mentioned in too many recipes, but you absolutely can—and should—bloom your coffee when preparing a French press!

The process is essentially the same as a pour-over. Just pour enough water to fully wet your coffee grounds, then wait 30 to 45 seconds before filling the rest of the carafe.

During blooming, gently stir the coffee grounds once when you first pour the hot water, and once after blooming to ensure the crust that collects on top is evenly mixed.

Does All Coffee Bloom?

Blooming is most obvious with coffee that has been freshly ground and freshly roasted. If you don't see the bubbly foam that indicates your coffee is degassing, then you may be using old or stale coffee.

It's likely that you've watched a coffee bloom before without realizing what you were seeing. This is particularly so if you're a fan of espresso, as blooming is what causes the distinctive, flavorful foam to accumulate on the surface of your espresso shot.

Factors That Can Affect the Blooming Process

A coffee bloom is the degassing process, so anything that affects the rate of degassing can also affect the bloom. Degassing begins as soon as the coffee bean is roasted, so the longer you wait to use the coffee, the more likely it is that much of the degassing has already occurred.

Other factors that may affect the rate of degassing:

Storage methods: Saving your coffee beans in an airtight container like our Atmos Vacuum Canister can keep them fresher for longer.

Temperature: Higher temperatures can increase the rate of degassing

Humidity: Lower humidity increases the rate of degassing, but too much humidity can allow mold or fungus to grow in the beans, so you need to find a middle ground
Roast style: Darker roasts won't degas as much as beans that have been lightly roasted

What if you don't see a bloom?

This usually means your coffee has already degassed. This happens if your coffee is not fresh or your coffee bag wasn’t sealed correctly, and your beans oxidized. This could also be an indication your beans are over roasted. Blooming, like all other aspects of brewing coffee, takes experimentation with different roasts and techniques.