What is “Blooming” in Coffee? And How Can Doing this Simple Step Drastically Improve Your Brew?  

Your coffee bed puffs up and starts bubbling up - what's going on? Learn all about the bloom and why it's such an important step that shouldn't be missed.
Coffee grounds blooming in a Hario V60
Photo by Devin Avery on Unsplash

Blooming – it’s when your coffee bed puffs and swells up, and even starts bubbling like some mad scientists’ potion. You may have read something along the lines of “let your coffee sit and bloom for 30 seconds” in a brew guide. Heck, my Moccamaster and Chemex brew guides have an explicit “stir and bloom” stage in my instructions.

On the surface, it seems to be a bit of a waste of time, adding an unnecessary level of complexity to your morning brew when you’re already feeling groggy from just waking up. So do you need to do it? Does it really benefit the taste of the coffee? (Spoiler alert: yes.) Why do baristas insist on doing it? 


What is Coffee Bloom (or Blooming Coffee)?

Blooming is almost exclusively spoken about in terms of handmade pourover coffee – using a V60, an AeroPress, or a Chemex, for example. You’ll rarely have to concern yourself with blooming on an automatic coffee machine, simply because there isn’t an option to do it. There are exceptions, like using a Moccamaster, but more on that later.

As mentioned, blooming is when you first pour water onto your bed of freshly ground coffee, and the bed starts to puff up and release bubbles. What is this, and why does it happen?

When coffee beans are roasted to bring out the aromas and flavours, there is a build-up of carbon dioxide gas, or CO2 in the beans. This gas will slowly be released over time. But once you grind the beans, and pour water over it, the gas is suddenly released at a much, much faster rate. This is what causes your bed of freshly ground coffee to expand and start bubbling when water hits it. And this is what we call “the bloom”, or the blooming phase.   

Here’s how I like to explain it in simple terms when training a new barista:

Blooming is the process where a bed of ground coffee expands and releases bubbles after water is first poured on it, in which unwanted gas is rapidly released

Note that I say “unwanted gas”. Carbon dioxide is indeed something that is unwelcomed when we brew coffee, simply because it causes the final cup to taste quite bad. Why is that?

Why Do I Need to Bloom My Coffee?

When brewing coffee, it’s important that water evenly saturates the bed of ground coffee. This is so that the water properly teases out the delicious aromatics and flavour compounds hidden in the beans. If you skip the bloom, and keep pouring additional water in, it will lead to an uneven extraction. With all the gas bubbling out, it almost creates a barrier that blocks the water from evenly spreading across the coffee bed. 

Hence, the reason why we recommend you wait about 30 seconds to give time for most of the unwanted carbon dioxide to dissipate. You can visually see this – when the bed starts to “deflate” and the bubbling slows down, that’s how you know you’re ready to continue pouring the water. 

Not to mention, excess carbon dioxide gives your coffee a very unpleasant acidic taste as well. Not something you want to scrunch up your morning!

Note that sometimes, the coffee bloom will be less visible, depending on the type of coffee you’re using, as well as the freshness (i.e. how many days have passed since roasting). We’ll touch on this a little more below, but for now, if you don’t see a whole lot of bloom or if it subsides really quickly, you can continue to pour your hot water – the 30 seconds is a rough guide, not an absolute rule. 

How Do I Bloom My Coffee?

Blooming is the first stage of your brew. The water you use for the bloom will be included in your final cup, so don’t chuck it out! The total brew time should include your bloom as well, so don’t tack on an extra 30 seconds to your total brew time, or you’ll risk over-extraction. 

  1. First, make sure the bed of ground coffee is flat, no matter what brewer you are using, be it a V60, a French Press, or an AeroPress. You don’t want a heap of coffee grounds towards the middle or skewed to one side. Tap the side of your brewer with your palm to even out the bed. This is called distributing the coffee.
  1. Once your water is hot enough (about 91°C to 96°C – never use boiling water!), pour in about double the dose of the dry coffee you’re using. 

For example, 60 g of hot water to 30 g of ground coffee. 

Or, 100 g of hot water to 50 g of ground coffee.

Or, you can visually estimate it too. Pour in just enough water until it covers the bed of coffee. Regardless of which method you choose, pour in a slow, circular fashion to wet the coffee bed as evenly as possible. 

  1. Set your gooseneck kettle down (I highly recommend getting one), step back for 30 seconds, and let the blooming do its magic! 
  1. Continue your pour and brew as you normally would. 

Easy! Here are a couple of additional tips that may help you:

Swirl Your Brewer

If you’ve taken the above steps correctly, you shouldn’t have to worry about disturbing your brewer during the blooming phase. However, if say, you didn’t have a gooseneck kettle and you accidentally poured the hot water unevenly over the coffee bed, don’t freak out. There is a fix.

Gently pick up the brewer, making sure it is still directly over your carafe/mug. You don’t want hot coffee dripping over your floor! 

Then, gently swirl the brewer about 2-3 times so that the ground coffee and water is evenly mixed. Place the brewer back down and you’re good to continue. 

Be careful not to swirl the mixture too vigorously or too many times, because then you’ll introduce a new problem called unwanted agitation – which leads to your coffee being over-extracted and bitter tasting. Your only goal is to ensure the hot water soaks evenly across the entire bed of coffee. 

Using a Digital Coffee Timer

I cannot begin to express just how valuable having a good coffee scale is to your coffee brewing journey. Sure, you can time your brew on a phone and have a separate scale, but having a dedicated coffee scale that can accurately measure the weight of your brew, and simultaneously track the total time elapsed is a game changer. 

This would allow you to measure the weight of the water poured for the bloom, and the total time of the bloom. 

Here are some I’ve personally used throughout my career and would recommend:

  • Timemore Black Mirror Scale
  • Acaia Pearl Scale
  • Hario V60 Drip Scale

I’ll do a full review of coffee scales sometime in the future, but you can’t go wrong with these 3 options. 

Blooming with a Moccamaster

Now, I’ve written an entire Crash Course on How To Use a Moccamaster, so go check that out if a Moccamaster is your preference for brewing coffee. The Moccamaster is an automatic drip coffee maker, and is one of the industry’s best. 

The way it dispenses water over the coffee bed takes into account blooming, so it will pulse the water and stop occasionally to allow the coffee time to bloom. So, you could just leave the Moccamaster to do its thing, knowing that you’ll still get a delicious cup of coffee. But, for some models where you can open or close the brewer’s valve, you can manually take charge of the blooming to your heart’s content. I go into a step-by-step guide you can follow in that article, so be sure to check it out. 

How Roast Level and Freshness Affects Blooming

Now, sometimes, you might notice an enormous amount of blooming where the coffee bed swells to almost twice its size. And other times, the bed may squeak out a few pathetic bubbles and that’s it. The amount of bloom you’ll see depends a lot on the type of coffee used, particularly its roast profile, and how many days have passed since roasting. 

Light Roasts

Coffee beans with a light roast will generally bloom less. Because the time they’ve been roasted is less, there is a lower build up of carbon dioxide gas, and so the blooming won’t be as intense. So you could adjust your bloom time accordingly. For instance, if the coffee has fully stopped bubbling at 15 seconds, don’t be afraid to cut your bloom time short by 10 seconds. You don’t want to be sitting there doing nothing – heat loss is something you need to take into account, too!

Dark Roasts

Dark roasts tend to bloom significantly more as the longer roast time means more carbon dioxide gets trapped. But this only applies if the beans are still quite fresh. Dark roasts degas a lot quicker than their lighter counterparts, which means that if you wait 2 weeks or so after roasting, you may even see less bloom than a light roast that has aged the same amount of time. This is also the reason dark roasts go stale quicker than light roasts. All the carbon dioxide, along with the aromatics, have escaped.

Ultimately, when you’re buying coffee beans, always buy based on the roast date, never the expiry date. With the roast date clearly marked, you’ll always know how fresh your beans are. Supermarket commodity coffee is the opposite – their goal is to sell the most coffee, not the best coffee, so you’ll usually see expiry dates a year down the line, which means the coffee has already lost all its flavour.

Wrapping up the Bloom!

In a nutshell, sparing that extra 30 seconds to allow your coffee to properly bloom is well worth it. It promotes an even saturation of the coffee bed, which will in turn, give you a tastier cup of coffee that is more well-rounded and balanced. There’s a reason why baristas never skip this step. And if you’re sourcing freshly roasted coffee from a specialty coffee roaster, you should adopt the bloom as part of your daily routine. Not only is it immensely satisfying to watch the coffee bed poof up, you’ll be drinking much better coffee.