What is a coffee bloom?

The coffee bloom might sound like something only a coffee pro cares about, but it's also a simple, little-known-trick you can do to unlock the flavors of your coffee at home.

Freshly roasted coffee has more carbon dioxide trapped in the bean. This is because the carbon dioxide builds during the roasting process when harvested green coffee beans are heated at high temperatures, and continues to build as the roast darkens.

After the roasting process, the coffee beans begin to de-gas and release carbon dioxide, quickly at first before slowing down. However, once you grind the coffee before brewing, it exposes more surface area for carbon dioxide to escape. The coffee bloom happens when a little hot water is first poured over the coffee grounds at the start of the brewing process. The hot water causes carbon dioxide to rush out of the coffee grounds. As the carbon dioxide escapes, the coffee grounds will rise and quickly bubble up to look like a “bloom”. 

Why is the coffee bloom important?

So why is a coffee bloom important? Letting carbon dioxide escape will improve a coffee’s flavor in two ways.

  • If grounds are not allowed to bloom before brewing, the gas will infuse a sour taste into the coffee.
  • Carbon dioxide repels water, which interferes with the brewing process. Water can freely extract the aromatics and oils in coffee only after carbon dioxide has escaped.

In a nutshell, letting your coffee bloom is a way to enhance your coffee's flavor, allowing it to taste sweeter and more robust.

How to bloom coffee in a pour over

Someone is pouring water from a Bonavita kettle into a coffee dripper.

The key to letting your coffee bloom is to first add a small amount of hot water to your coffee grounds, then waiting a short period for the coffee to de-gas before adding the rest of the water. 

For pour over coffee, we like to use a timer and a scale to ensure the right amount of water is being added to the coffee grounds, and the coffee has adequate time to bloom.

Begin pouring water slowly over the coffee, starting from the outside and moving in a steady spiral inwards and back out again. Stop pouring when the scale reaches 60 grams. Make sure all the grounds are saturated. The pour should take about 15 seconds. Give the coffee an additional 30 seconds to bloom before moving on to your subsequent pours.

How to bloom coffee in a Bonavita coffee brewer

Our full line of Bonavita coffee brewers have a feature called the pre-infusion mode. The optional pre-infusion mode wets your freshly roasted ground coffee to allow degassing before brewing, akin to the coffee bloom.

If you are brewing with freshly roasted coffee, or you would like to pre-infuse the coffee, press and hold the power switch for 5 seconds. At that point the power switch light will flash and 2 beeps will be heard indicating that you’ve enabled the pre-infusion mode. Press and release the power switch a second time to begin brewing.

You can disable the pre-infusion mode by pressing the power switch until the light blinks (5 sec.) and a single beep is heard. The brewer will remain in this mode until the mode is turned off or the brewer is unplugged.

Now you're on your way to a complex and full-bodied cup of coffee at the touch of a button.