What Exactly Is A Coffee Bloom, Anyway?

03/19/2015 09:17 am ET | Updated Mar 19, 2015

Whether you're a coffee addict or just a casual drinker, you've probably heard the term "coffee bloom" at some point. Most likely, if you were in the presence of a holier-than-thou barista or a serious coffee snob, you weren't only subjected to this jargon. You were expected to understand what it meant. For all of you bloom newbies out there who don't want to ask for an explanation, we at HuffPost Taste want to clear things up. In our latest installment of "what in the world is that food thing you've heard of a thousand times but actually know very little about," we're putting on our coffee snob hats.

A coffee bloom is the fast release of gas that occurs when hot water hits coffee grounds. It looks like this:

The Bloom. That beautiful beautiful moment during a brew. #fresh #coffee #bloom #v60 #hario

A video posted by the Roasters Pack (@theroasterspack) on


When coffee beans are roasted, CO2 gets trapped inside. From then on, the beans will slowly emit the gas over time -- a process known as "degassing." When ground, the beans will emit gas more quickly, and when met with hot water, all of the remaining gas will escape rapidly. This is the bloom, and the more gas that's escaping, the bigger the bloom will be.

All of this matters to you and your friendly coffee freaks for two reasons. One, "the majority of a coffee bean's flavor compounds are trapped in the CO2 gases," MentalFloss says. So, more gas = more flavor. Two, the amount of gas can indicate how fresh the beans are.

Beans that have been sitting out for a long time will have more time to release gas. (Stop laughing. It's going to be okay.) Thus older beans will produce less gas and a weaker bloom. Age isn't the only factor that determines how much gas escapes from beans. Storage is important, too. Beans kept in hotter temperatures will release gas more quickly. This is one reason to keep your beans in cool temperatures. Beans should also be kept in sealed bags with one-way valves that don't let oxygen in, but allow for CO2 to escape.

Of course, it gets more complicated than the simple equation that more gas signifies fresher beans and more flavorful coffee. The type of roast is a key factor, as well. Darker, more oily beans won't release gas as quickly. They've also endured a longer roasting process, which means they contain more CO2 in the first place. Thus, darker roasts tend to have bigger blooms than lighter ones. When comparing blooms, you need to also keep the type of roast in mind.

Finally, to confuse matters, "bloom" can also be a verb. You can create a bloom by blooming -- or adding hot water to coffee grounds. There are different techniques for different coffee-making methods. If you use a pour over, you should pour water over the grounds in a circular motion. If you use an automatic coffee machine, you should pour just enough water to wet the grounds, let them rest for a couple minutes and then use the machine as you otherwise would have.

Need a cup of coffee yet? To summarize:

More gas = more flavor and fresher coffee.
More gas = a bigger bloom.
So a bigger bloom = more flavor and fresher coffee.

And now when your snobby coffee friends are fawning over a bloom, you can remind them that it's just gas.

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