The Bloom. It’s referenced in nearly every specialty brewing guide, it’s canon for every barista, and it’s the difference between a sub-par cup and a balanced extraction. But what exactly is it?
The Bloom refers to the stage at the beginning of a brew where hot water triggers the rapid release of gases from grounds1. Characterized by bubbles pushing grounds upwards and outwards, the bloom is named for the visual similarity to a flower opening2.
Why is it significant?
The main player here is carbon dioxide2. CO2 locked within the beans begins to slowly leach off after roasting. This is integrally linked to coffee freshness, as CO2’s presence prevents molecules within the bean from coming in contact with – and being broken down by – oxygen3. For maximum freshness and flavor payoff, the goal is to maintain levels of carbon dioxide as long as possible, and then to exchange CO2 for water to extract the full potential complexity and sweetness2.
(It’s for this reason that our bags have a one-way valve – it lets the released gases leave naturally, but doesn’t allow air back in.)
While carbon dioxide plays a key role in freshness, too much during the brewing process can badly throw it off, and here’s why.
> It prevents water from coming into contact with sugars, flavor molecules, and acids. This prevents those key elements from making it into the final cup, which is kiiiinda the whole point.
> It repels water, causing grinds to float and resulting in uneven extraction throughout the sample. Underextraction leads to sourness – overextraction to bitterness. Uneven extraction can mean both.
> It tastes bitter – pleasing in carbonated water, but a unwanted consequence in a cup of coffee. Releasing into the air cuts down on bitterness, and improves the experience significantly.
How do I bloom?
While the parameters are often tweaked, here are the methods we use:
- Put grinds into brewing device
- Pour twice as much water as coffee grounds over the grounds, saturating all evenly
- Wait for 40 – 60 seconds, typically until new bubbles have stopped appearing
- Continue with preferred brewing technique
- Put grinds in
- Fill with water
- Set timer for four minutes
- At the two minute mark, gently press the grounds that have risen to the surface under water with the back of a spoon. Two or three swipes should be plenty!
- Place the lid on top to reduce heat loss
- Press down bar when the times goes off
Contrary to other methods, the Aeropress doesn’t seem to be significantly affected by blooming. The only reason to include a bloom is to prevent overflow, and this can easily be achieved by adding a little water at the beginning, allowing a few seconds to off-gas, and then filling it up all the way.
- Put grinds into the filter
- Pour enough hot (not boiling) water over the grinds to saturate
- Start the typical brewing cycle
If you’re not seeing a bloom, chances are your coffee is stale. For the freshest cup, check out our guide here!
Will blooming your brew up your coffee game? Test out the difference this week (with some delicious Ruli Mountain perhaps?) If you’re already blooming, what techniques do you use? What have you learned?