Coffee people generally have two favorite blooms: the fragrant flowers that blossom on coffee plants (oh, that smell!), and the first part of the brewing process (oh, that smell!). Coffee flowers are beautiful, and we hope you all get to experience them someday, but today we’re going to talk about the brewing bloom — what it is, what it does (or doesn’t do), and how to play around with it.
Have you ever made a pour over of a very fresh coffee, that was roasted only a day or two before? You may have noticed that when you first poured water into the grounds in your filter, they kind of poofed up like a science experiment: That, my friends, is the result of CO2 escaping the freshly roasted coffee, which makes it kind of fizzle and expand in the bed.
Carbon dioxide is a by-product of coffee roasting — which you know from reading this piece about degassing. The fresher the coffee is off roast, the more CO2 is still trapped in the beans and grounds, and the poofier this part of the brewing process will be. We call this poofing up “the bloom,” and the grounds really do seem like something is about to sprout out of them, like the beginnings of a baby plant pushing out from wet spring soil.
The bloom is one aspect of coffee brewing that nerds love to ponder: There are countless theories about how it impacts flavor, opinions about the length of time it should be, even brewers designed to manipulate it. It’s generally accepted, however, that skipping this step is a no-no, and that including a bloom in your brewing ritual will help you achieve better coffee.
Why? Well, imagine a narrow corridor through which you can only pass through single-file. If there are people streaming out, there isn’t any room for you to go in. Coffee grounds are a bit like that: You want water to enter them and pour out as delicious, perfectly extracted coffee on the other side, right? But if CO2 is streaming out of the coffee grounds, water can’t pass through: There’s too much resistance coming in the other direction. Pouring just a little bit of water, however, helps activate the CO2 release process, and if you’re patient enough to wait just a little while, enough of that carbon dioxide should stream out to make way for the water to stream right in and do its job. You follow?
How long you bloom, and with how much water, will probably always be up for debate. Some professionals don’t care to wait very long, while others love a long bloom. Former World Barista Champion James Hoffmann has admitted to being “lazy” — which is categorically untrue — and wanting to brew for the least amount of time possible in order to still get good results; cupping-spoon designer and coffee philosopher Umeko Motoyoshi has famously called for a “long-ass bloom” for a sweeter result.
In any case, remember that the longer you bloom the higher your extraction yield will be in the cup, but also the more heat you’ll lose in the brew bed and your kettle. One thing pretty much everyone agrees on is that some bloom is better: Skipping this step usually results in under-extracted, underwhelming flavor.
Personally, I adjust my bloom to respond to the coffee’s behavior: I like to add just enough hot brewing water to saturate the grounds (usually about twice the volume of the coffee in my recipe, so if I’m brewing 30 grams of coffee, I’ll aim for 60 grams of water for my bloom). Rather than watch the clock, I watch the coffee as it puffs up. When I see it “burp,” or finally start to settle back down, that’s when I’ll add my first pulse of brewing water.
I find that for very fresh coffee, that burp might happen at around a minute; if a coffee is a couple of weeks out of the roaster, it might take 20 seconds. Remember to take care to adjust the rest of your technique to hit your target brew time so you don’t under- or over-extract the coffee, but otherwise, have fun and play around to see what works best for you!