What Is A Coffee Bloom? - HOMEGROUNDS

What Is A Coffee Bloom?

I spend a lot of time on this blog talking about the benefits of using coffee that is as fresh as possible.

I urge you to buy your beans as soon after roasting as you can (or even better, roast your own) and to grind just before you brew.

I’ve shared reviews of beans and coffee equipment to help you get the best from your cup of Joe.

Which is why it is now my duty to tell you about the drawback of truly fresh coffee:

Carbon Dioxide.

Not one to bring you a problem without a solution, read on to learn how to degas your fresh grounds for premium flavor.

In other words, how to bloom coffee.

Coffee Bloom Explained

You may have come across the phrase, ‘coffee bloom’ during your research into the perfectly brewed cup. It’s more common among devotees of pour-over methods. 

It simply refers to pouring a small amount of water over your coffee, and allowing that to sit for a short while before you continue brewing.

coffee bloom

If you’ve ever seen coffee when it’s blooming, you will have noticed that the grounds swell, and bubbles rise to the surface of the liquid.

Those bubbles are Carbon Dioxide (CO2) being released by the beans.

New to pour-over?

Catch up by reading our beginner's guide before you go any further. Don’t worry, we’ll wait.

Carbon Dioxide

Here’s the coffee bloom science.

CO2 is inside every coffee bean as it grows. From the moment the beans are roasted, the gas begins to escape.

In fact, the darker your beans are roasted, the less CO2 you can expect to find in them.

When beans are ground the surface area increases, and they degas far quicker than whole beans.

The problem with this natural degassing is that the volatile compounds that give coffee its flavor escape with the carbon dioxide, making the coffee go stale.

CO2 is our friend, right until the point where we come to brew.

There are two ways in which the gas negatively impacts the flavor of your drink.

  1. Carbon Dioxide tastes sour. While that’s refreshing in a glass of carbonated water, it isn’t a flavor profile that we want from our premium beans.

  2. The gas stops water from coming in contact with the coffee. Until the gas has released, the water cannot do its job of extracting all the delicious compounds necessary for your brew.

For those reasons, it’s worth adding another 30 seconds to your brewing time, in order to release the gas.

How to Bloom Coffee

There’s nothing complicated about getting your coffee to release the gas.

Here’s how to go about it:

  • Put your freshly ground beans into your favorite pour-over coffee maker.
measuring ground coffee
  • When your water is at the right temperature, measure out twice as much water (so for 25g of beans, 50g of water).
measuring hot water
  • Pour the water over the coffee.
  • Wait for 30 seconds. You should see the coffee puff up, and bubbles of gas release from the surface.
  • Pour on the remainder of you water and brew as normal.
adding water to the coffee
PRO TIP - To get a really controlled pour, consider getting a gooseneck coffee kettle

Watch this video for a full demonstration of blooming from Coffee Lovers TV.

There are a number of factors that affect how much gas is released when you bloom.

  • I’ve already mentioned the freshness of the coffee.
  • Roasting also releases CO2, so the darker you like your roast, the less bubbling you will see when you bloom.
  • The bean hardness can also make it more difficult for the carbon dioxide to make its way through the bean.
  • Other things can affect the process too, like the temperature of the water, and the heat and humidity on the day you brew (the colder means less gas release).

In general, though, seeing a lot of bubbles means that you are working with really fresh coffee.

When Not To Bloom

Adding a bloom into any brewing method won’t have a negative impact.

You may not notice the difference in methods other than pour-over, though. The reason for this is that pour-over methods put the water in contact with the beans for the shortest length of time.

If you have something (read CO2) stopping the water from extracting flavor, it’s going to show up in the taste. 

If you’re wondering how to bloom coffee using a French press, you just follow the method above.

But immersion methods, or more intense methods like percolators or espresso machines don’t really benefit as much as pour-over.

The only exception to that is cold-brew.

Because hot water is such a help in removing the gas, it can be useful to use a hot bloom, cold brew recipe. Bloom your coffee with hot water before you go on to cold brew it, to ensure a real clarity of flavor.

The Art of the Pour

Some coffee guru’s make pouring water over coffee look like an art form. Watch this video to see how:

While you don’t need to make your brew quite that much of a ritual, you do want to make sure that the water is spread evenly through the grounds.

This will help to get an even release of gas through the beans.

As we mentioned before, a gooseneck kettle will help with the pour. We’ve reviewed 5 of the best for you.

Too long, didn't read?

This is our top pick.


The Coffee Gator’s Pour Over Kettle

The Best Value For Money

The Coffee Gator’s Pour Over Kettle

A built in thermometer lid combined with the shape means you can somewhat control your water temp + flow, however its not 100% accurate.


Do you see what I did there?

Nirvana played, ‘In Bloom’ and it’s another word for heaven.

Coffee heaven?

No. Never mind.

The key to a purer coffee flavor could just be another 30 seconds to your brewing routine.

Give it a try the next time you’re pouring-over, and let us know if you can taste the difference.

Leave us a comment below if you’re a die-hard bloomer, or share your experiences with gassy coffee. We’d love to hear from you.

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