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What Is Coffee Bloom and Why Does It Matter?

Driftaway coffee bloom

Using a gooseneck kettle, you pour hot water in gentle circles over freshly ground beans. The grounds rise up, bubbling slightly and releasing a tantalizing aroma. If you’re a pour-over coffee fan, you’ve certainly had this experience. But what exactly is happening, and how does it affect your coffee?

Coffee bloom is a vital part of the brewing process, giving your coffee life and helping you make sure your beans are fresh. Keep reading to learn all about this interesting phenomenon!

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What Is Coffee Bloom?

The bloom of coffee is when all of the gases that have been trapped inside the coffee bean start leaking out. This process begins when hot water is introduced to the grounds. Then the bean absorbs and expands and at the same time, pushes out all the CO2 trapped inside.

Where does the CO2 come from? It happens during the roasting process. Dark roasts, for example, produce more of a bloom, as they are roasted for longer and more CO2 gets trapped inside.


Why Does It Matter?

This is how we can tell how freshly roasted coffee beans are. The reason it matters is that there is a bunch of flavor in those gases, as well as aromatics. The less gas in your coffee, the staler it will taste. This makes sense because if a coffee doesn’t bloom, it’s probably old. Of course, coffee can go stale in many ways, and there are multiple factors to consider when discussing coffee bloom.


Why Does Coffee Go Stale?

Coffee goes stale for the same reason that coffee blooms: escaping CO2. The moment coffee beans are pulled out of a roaster, they start losing the gas built up inside them. Therefore, you can tell how fresh your coffee is by how intense the bloom is. With certain extraction methods, you actually want to wait for the coffee to lose some of its gaseous nature, as an excessive amount can lead to a drink tasting ripe.

You will also probably not get much or any bloom out of pre-ground coffee. The gas inside a coffee bean normally sticks around for 10 days to two weeks, but once the coffee is ground, it begins rapidly escaping. This is also why the coffee world strongly urges people to invest in a grinder and buy their coffee whole bean.

coffee bloom Chemex

Best Way to Bloom

The brewing method that showcases a bloom most easily is the Chemex. It is the first thing that happens when you swirl the hot water over the grinds. This process is even more neat to watch when you have a better understanding of what is going on. As the coffee expands, you can see the flavor going into the pot and smell it while it’s happening.


What Variables Affect Coffee Bloom?

All sorts of things affect the bloom of a coffee. Many do so while it’s just sitting around. So, what are the variables?

  • Temperature: If beans are in a hot area, they will lose gas quickly, which is why it is recommended to store whole bean coffee in a cool place. The refrigerator seems ideal, but coffee is very sponge-like and will absorb the flavor and smell of whatever else is in the refrigerator.
  • Roast: The darker the roast, the more gaseous it is. Although, interestingly enough, the darker the roast, the slower that the gas escapes, meaning there is less of a fascinating bloom with darker coffees.
  • Bean hardness: If a bean is really hard, gas will have a difficult time escaping.
  • Humidity: In really dry areas, beans de-gas very quickly. There are items on the market that help you keep your beans humidified.

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Conclusion

There you have it: you can now add coffee bloom to the list of things you now know about coffee. You can talk to your friends through a brewing process and be able to spot stale coffee the moment water touches it. Next time you brew a pour-over coffee, take a moment to appreciate the science behind your favorite flavors. Happy brewing!

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Kate MacDonnell

Kate is a lifelong coffee enthusiast and homebrewer who enjoys writing for coffee websites and sampling every kind of coffee known to man. She’s tried unusual coffees from all over the world and owns an unhealthy amount of coffee gear.

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