When accounting for bloom, why is the common instruction to stir with very little water?

Question

There is already a question on What is coffee bloom here, and one about why "blooming" the grounds is necessary over on seasoned advice. A currently unanswered question here is is blooming actually necessary in French Press, which an answer to that may help answer this one.

A fair amount of instructions I've seen that refer to this step instruct you to stir after adding just enough water to get all the grounds wet. However, there are accounts of people getting the same effect just stirring after all the water is added (in non-drip styles of coffee).

Is there a significant difference between blooming with some water and blooming with all? I like being able to rinse off the stirrer with the rest of the water, but I'm curious nevertheless.

Answer 1

Blooming is the outgassing of CO2 (carbon dioxide) from the ground coffee in response to hot water being added. The more recently the coffee has been roasted, the more bloom you can expect. It doesn't make a huge difference ultimately if this is done quickly or slowly when you brew your coffee. What I have noticed myself is that it's sometimes diffcult to predict how much foam is going to be produced when the water is poured over the grounds. More than once I have misjudged the amount of bloom and made a foamy brown mess on my countertop. If you just add enough water to wet the grounds first, you accomplish two things.

First, all the coffee is wetted at nearly the same time which better controls how the flavors are extracted, since different flavor profiles extract at different rates. Sometimes adding all the water at once creates lumps of dry coffee mixed in with the bloom and wetted coffee and it takes a bit of stirring to get all that wetted.

Secondly, adding a small amount of water controls how quickly the bloom will occur. You'll get most of the bloom done well within the pot and you'll avoid the huge foam ball at the top of your brew that might overflow the pot (or AeroPress in my case), but really this is more of a technique thing than a chemistry thing.

Answer 2

A good reason to use a small amount of water when blooming a pourover is to avoid channeling. Water flowing through coffee will follow the path of least resistance, so when you have gaps being formed by CO2 bubbles, some water is going to quickly and disproportionately rush through those low density areas. Degassing as much as possible with a minimal amount of water mitigates the detrimental effects of channeling and allows the coffee to return to a more uniform density before proper brewing begins.

Obviously channeling is not an issue with immersion methods like French press, Aeropress, Clever, etc., so you're unlikely to see as dramatic a difference.