You keep hearing about it, but still don’t fully understand what coffee blooming is. We’re here to help clarify so next time that know-it-all-coffee-friend goes off on a blooming spiel, you can dethrone them as the know-it-all-coffee-friend.
What blooming is:
When coffee grounds come in contact with hot water, they release carbon dioxide and often bubble and expand. Coffee blooming is the act of dampening your coffee bed to provoke this release of carbon dioxide.
What causes it:
When coffee beans are roasted, the organic material of the bean is heated and releases carbon dioxide.
Beans will continue to release natural gases, or “degas”, gradually over 14 days (but most of the gas is released in the first 10). When you grind your coffee, or add hot water it speeds up the degassing process. (This is why you should always grind your coffee right before you brew).
Hot water in particular causes beans to immediately release most of their carbon dioxide. This creates a “bloom” when those first drops hit your coffee grinds.
Because CO2 is escaping quickly, it repels water away from the grounds. Carbon dioxide pushing water away is also known as turbulence. This is an issue when you’re trying to extract delicious coffee flavors and textures (the more water to coffee interaction, the more extraction).
We bloom coffee to give the grounds time to make space for water. Additionally, carbon dioxide tastes sour, so blooming prevents CO2 from infusing into your coffee.
How to bloom:
To bloom coffee, start pouring at center of your coffee bed, working your way out to the sides. Pour about two times the the amount of coffee you use. Wait 30 seconds for coffee to “bloom” and release CO2.
Grounds should be uniformly soaked, but not dripping wet. Here’s a handy video from Coffee Experimental for a visual aid:
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.