What is a “Coffee Bloom”? Why Does it Matter?

A coffee bloom is, in fact, different from a flower bloom. But it’s nearly as pretty. 😉

Why do the grounds get big?

If you’ve ever made manual pour over with a Kalita Wave or a similar device, with fresh roasted coffee, you’ve certainly seen a bloom. If you’ve had someone make you a fresh-ground pour over in a coffee shop, they probably saw a bloom, and may have showed it to you. It’s a cool effect. But what is a coffee bloom?

Here’s my best word-picture. You’ve got dry coffee grounds sitting in a filter. As you pour a small amount of water in, the now-wet grounds expand until they’re about double or triple their initial volume. The shape of them is likely to be dome-like, though part of that appearance could be caused by my Wave. And here’s a real close-up picture:

What causes your coffee grounds to bloom?

In short, a bloom is the release of gas when your coffee grounds come in contact with water.

The slightly longer explanation, is that freshness of your beans is a big factor in whether or not you’ll see a bloom. The reason: beans essentially trap some gas (carbon dioxide) inside them when roasted. As a bean sits, it’ll slowly lose that gas into the surrounding normal air we breath (which is mostly nitrogen). As nitrogen-based normal air replaces the carbon dioxide, you’ll see less active blooming when you mix ground beans an water.

If you wanted to speed the loss of CO2, you could do one thing: grind the beans before you let them sit. By putting more of the surface of the roasted bean in contact with the surroundings, it will “off-gas” (do that air-exchange) much more quickly than it will when kept whole.

This is also the reason that the best way to get a bloom is to have fresh-roasted, fresh-ground beans. I love the bloom. To me it’s a great sign that I’ve got a fresh (and thus more flavorful) cup of coffee ahead. #Don’tFeartheBloom

Why you should bloom coffee

The basic reason to let your coffee bloom (or “breathe”) is that it’ll make sure that it’s most ready for the prime-time extraction of a pour-over or some other method. Better to let all the gas off up-front, then as you (say) press your AeroPress down.

However you make coffee, if you’re using fresh roasted (in the last few weeks) and fresh ground (in the last few hours) you will get a bloom. If you don’t include it as step in your process, it’ll likely just be a confounding variable when you think about what makes your coffee good.

If you don’t see a bloom when you follow one of the procedures we outline below, it’s likely that your coffee is “stale.” Not so stale you should discard it (I regularly drink great-tasting coffee that doesn’t bloom). But stale enough I won’t see a gas-dance.

Very-stale coffee (much you’ll get at a supermarket, having sat on shelves for months) will lose its flavor. But seeing a bloom is more a showing of abnormal freshness. Coffee that doesn’t bloom is still often plenty-fresh to taste good. But coffee not blooming is a tangible sign that it could be truly stale and not-great.

How to bloom your coffee for pour over

brewing pour over coffee at home

Pour over is my favorite way to brew coffee (the ceremony!). As such, its bloom is the one I see the most. Here’s what I do:

  1. Add the coffee to a (wetted) filter in my Kalita Wave
  2. Pour in double the weight of water that I have coffee grounds. (So, for 24g of coffee, I typically do ~50g water.) Make sure when you wet the grounds you leave no dry spots.
  3. OPTIONALLY: Stir. Opinions diffe. I rarely stir, because I’m lazy. Some swear by it to get the best bloom in. I know (from experience) that it makes a less pretty-and-domed shape.
  4. Sit back and watch the mix of coffee and water grow and puff. If it’s really big, call everyone else in the house to watch, and then apologize as they arrive too late. (An average bloom time, in my experience, is about 30 seconds.)
  5. Pour as normal!

Blooming coffee in the (inverted) AeroPress

The way we (David and Megan) make AeroPress coffee is most often with the “inverted” method. As such, we’re making a solid cup-like contraption. So it’s pretty simple:

  1. Pour in coffee grounds.
  2. Pour in a small quantity of water, about 50g or mL. If your coffee is FRESH (freshly-roasted, and freshly-ground) it’ll expand up for twenty-ish seconds.
  3. Mix with the AeroPress stick the water and grounds.
  4. And add water, flip, and press, as normal.

The French Press coffee bloom

Because an inverted AeroPress is essentially just a big cup, like the French press, you can easily follow the steps above.

A final note: Help make this better?

I take very seriously the need to be accurate and useful. I hope this post has been. But I have some concerns, most notable is that I did a fair bit of research for this article found only articles written by people who seemed to have only about as much knowledge as me.

I know there exist coffee experts in the world. Someone who can confidently and with authority tell me if the barista who told me “you don’t want to drink that, it was roasted too recently” was correct or spouting bullsh*t. And while I aspire to be such a person, today I am not. Please comment with articles, knowledge, or pointers to such people if you have them. I really appreciate it!

Random sidenote

There’s an Indian romance movie from 2015 called Coffee Bloom. That’s the source of the mysterious image I dropped at the top 😏

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