What Is A Coffee Bloom And Why It Matters

what is the coffee bloom?

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Are you struggling to brew a cup of coffee at home that tastes just as good as a cup from your local coffee shop? You might think you’ve covered everything, ticked every box, and got yourself the best gear you can afford, but have taken a look at your coffee bloom?

Coffee blooming is a crucial variable often overlooked by many home coffee enthusiasts. However, this process shouldn’t be overlooked. 

Once you understand the benefits of blooming your coffee, you’ll bring life into your once dull and sour brew, turning it into a perfect tasting cup that will impress almost any loyal coffee aficionado.

In this post, I’ll keep things simple as I walk you through everything you need to know about the coffee bloom: what causes it, why it matters so much for taste, plus pro tips for getting the perfect bloom when brewing.

Understanding this brief first stage of brewing can elevate your coffee from drinkable to downright delicious.

Let’s dive in!

✔ Quick Answer

A coffee bloom is the release of carbon dioxide gas trapped within coffee beans and grounds when hot water is first poured over them during brewing, causing bubbles and foamy swelling.

What Causes Coffee To Bloom?

I’m sure you’ve heard baristas at your local coffee shop mention the “bloom” when they’re talking with colleagues behind the counter, and you probably found yourself momentarily confused.

After all, it’s a strange term to use when brewing coffee, it’s something you would expect to hear in a florist rather than at your local Starbucks!

So, what is a coffee bloom? You’ve seen this reaction before when your coffee grounds start to swell and bubble up, but probably haven’t understood the reason causing it.

coffee bloom bean ground

Here’s the lowdown. 

The coffee bloom is a natural part of any brewing process, and the bloom phase starts when the hot water hits the grounds, which in turn causes gases locked inside to be instantly released.

As you introduce a small amount of water to your coffee grounds, CO2 is expelled from the cells of the coffee – the fresher your coffee, the bigger the bloom!

​In most cases, the bloom will last for only 30 seconds or less, and in that time, you’ll see your coffee grounds start to bubble and expand into a dome-like shape.

However, if you don’t see your coffee blooming or bubbling at all, it most likely means that your coffee isn’t fresh. Most of the degassing (releasing of CO2) has already occurred, and unfortunately, along with most of the flavor compounds that were once locked within the beans, will have also deteriorated.

So blooming coffee is a good thing to do, and it can tell you a lot about the quality of the coffee beans.

The Grind And The Roast Matters

The key to a terrific coffee bloom experience paired with a rich and flavorful brew is to keep the freshly roasted coffee whole for as long as possible.

This means only buying whole roasted coffee beans, ideally within one week of the roast date, and then grinding just before needed.

bloom can help

Keep in mind that once the coffee has been ground, there is more surface area. This will cause the locked-in gas to release quicker – essentially, the coffee no longer has a protective shell keeping the gas locked inside.

For me, I find the science behind coffee blooming fascinating, and understanding how carbon dioxide interacts with your coffee is something worth learning.

Let’s take a closer look.

Carbon dioxide has a sour taste. So when your coffee doesn’t bloom, say due to old stale coffee, or you haven’t left enough time for the blooming to degas, the CO2 will infuse the flavor of your coffee, giving it a sour taste.

Also, carbon dioxide repels water, which isn’t a good thing when you’re trying to wet the grounds in your coffee brewer, and in most cases, this will cause some under extraction.

Remember, it’s the water that extracts the aromatics and flavors from the coffee, so if the carbon dioxide hasn’t had a chance to disperse, the water won’t fully interact with the coffee.

Factors That Affect How Coffee Blooms

Blooming coffee isn’t always a given. As I’ve already mentioned, the freshness of your whole bean coffee is a crucial variable, but many other factors can also affect the bloom.

I’ve scrutinized the blooming process countless times, and over the years, I’ve found the following to impact the rate at which the gas is lost from the coffee beans as soon as they’ve completed the roasting process.

grind your coffee beans

Coffee Bean Origin

Over the years, I’ve noticed that beans from different parts of the world bloom differently. 

For example, Central American beans like those from Guatemala and Costa Rica tend to foam up rapidly and bubble vigorously. They are grown at high altitudes, which allows more gases to build up inside them.

On the other hand, Indonesian beans often bloom more subtly. Indonesia’s heavy rainfall causes the cherries to ripen quicker. The faster maturity means less gas is trapped before harvest.

Another thing I’ve noticed is that processing plays a big role too. Naturally and honey processed Ethiopians keep more gases, since the fruit stays on longer during those methods. Whereas the washed method removes the fruit faster, releasing gases sooner.

The important thing is, no matter the origin or degree of bubbles, be sure to bloom all coffee properly.

That short first soak leads to tastier brews down the line!

Coffee Roast level

I’ve seen firsthand how roast degree influences blooming activity. Light roasts tend to bloom more vigorously – they’re stopped early, leaving more retained CO2. 

Medium roasts bloom moderately. Go much past the first crack into dark territory, and you’ll see minimal bubbling.

Why’s that? During roasting, CO2 builds up inside the beans.

Take them far into second crack and beyond, and most of that gas gets roasted off. Without internal CO2 to drive the bloom, you won’t observe much activity.

However, don’t assume less bloom equals staleness! 

For darker roasts, a lack of bloom is perfectly normal, even when freshly ground. Plus, darker roasting produces oils that can naturally tamp down bubbles at the surface.

Temperature And Storage

Proper coffee storage is vital to not only an impressive bloom but also to the overall freshness of your coffee.

Storing coffee in a hot environment will allow the gas to escape faster. I suggest that you keep your beans stored inside an opaque container at the back of a cool pantry or cupboard.

These are my recommended coffee storage containers.

Grind Size

And last but not least, the size of your ground coffee.

Even something as simple as how fine you’ve ground your coffee will affect just how quickly it will release carbon dioxide.

Fine grinds will release gas from the surface area far quicker than coarse ground coffee because there is more surface area for the carbon dioxide molecules to condense and stabilize.

To Bloom Or Not To Bloom?

I’m sure if you’ve gotten this far, you will already know the benefits of blooming your coffee.

The brewing method is pretty straightforward and involves adding just enough water to moisten your freshly ground coffee (rule of thumb: 2 grams of water to 1 gram of coffee – read more on coffee ratios).

​Depending on your coffee maker, the coffee bloom process will be slightly different.

So keep on reading, and I’ll briefly cover how to bloom coffee in a French Press, pour overs like the Chemex, V60 as well as automatic drip machines.

How To Bloom Coffee

The blooming process does vary slightly depending on what type of coffee brewing method you are using.

Let’s take a look at three familiar coffee makers:

Pour Overs (Chemex, Hario V60, Kalita Wave, etc)

For pour-over coffee with brewers like the Hario V60 or the Chemex, slowly pour hot water in a circular motion starting at the outer edge, being careful not to hit the paper filter, and slowly working your way to the center.

The trick is to use just enough water so that the coffee grounds are saturated and uniformly soaked, but they don’t become too wet so that coffee starts to drip through the filter prematurely.

Let the coffee bloom for roughly 60 seconds. Once the bloom has finished, continue slowly pouring water using your gooseneck spouted kettle and the mentioned pour-over technique or using a figure of eight pour.

French Press

For the French Press, the blooming process is very similar.

Once you have added your coarse ground coffee to the French Press, slowly pour a small amount of hot water over the grounds.

You need to add just enough water to dampen the coffee – try to aim for a wet sand consistency or about 2-part water to 1-part coffee.

If your coffee is fresh, you will immediately start to see the coffee grounds bloom.

Let the process play out for about 20 seconds and gently coax and stir the grounds to make sure that they all contact with the water.

Once you’re satisfied, complete your regular French Press brewing regime.

Automatic Drip Coffee Makers

Yes, it’s also possible to bloom coffee using a push-button automatic drip coffee maker.

Place your paper filter into the drip basket (get better results using a Gold Filter like this) and add your ground coffee.

Slowly pour in just enough water to soak the grounds but not too much that it will penetrate all the way through and drip through the filter into the carafe.

Allow the coffee to bloom for roughly 60 seconds, and continue with your regular brew cycle on your machine.

When you let the coffee bloom in an auto-drip brewer, you can definitely taste the difference compared to not blooming.

Pre-infusion of water will form an even pool on top of the coffee grounds rather than the few drip depressions created by the machine.

This even pool of water will allow for an evener extraction and an ultimately better-tasting cup. The good news is that many of the newer push-button coffee makers have preinfusion features already built in, so keep an eye out for that. 

Pro Tips for Perfecting Your Coffee Bloom

Now that we’ve covered the science behind blooming let’s get practical. Follow my tips below for coaxing the most flavor during the bloom phase.

Coffee Bloom TipsRecommendation
Ideal 2:1 Bloom RatioUse twice as much water as coffee (2:1 ratio by weight). E.g., for 15g coffee grounds, use about 30g water. This ensures thorough, uniform saturation.
Evening Out Your Coffee BedAfter pouring bloom water, stir the slurry for 15 seconds. This helps wet any dry spots on the bed of coffee, ensuring balanced extraction and preventing channeling.
Water TemperatureUse water between 195°F to 205°F (90°C to 96°C). Ideal for extracting flavor without scalding the coffee.
Pouring TechniquePour water gently in a circular motion for even coverage and to avoid channeling.
Bloom DurationAllow the coffee to bloom for 30 to 45 seconds for effective CO2 release and extraction initiation.
Grind ConsistencyUse uniformly ground coffee for even extraction. > My recommended coffee grinders


So there you have it, understanding and perfecting the coffee bloom is a simple yet impactful step in brewing a superior cup of coffee. 

This brief initial phase, where gases escape and the coffee grounds swell, sets the stage for a balanced and flavorful extraction. By paying attention to factors like the water-to-coffee ratio, water temperature, pouring technique, and bloom duration, you can significantly enhance the quality of your homemade coffee.

Remember, the bloom not only indicates the freshness of your coffee but also plays a vital role in the overall brewing process. It’s a fascinating procedure that can elevate your coffee experience from ordinary to exceptional. 

So, next time you brew, take a moment to appreciate this small but mighty step in the coffee-making journey. With a little practice, you can turn your daily coffee ritual into an enriching sensory experience.


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