Percolation vs Osmotic brewing method: is it the same thing?

Question

I have just learned a pour-over brewing method called "Osmotic Flow" as in the link below: https://cafec-jp.com/brewing-guide/

The article said it used osmotic pressure to extract coffee essence from grounded coffee, as opposed to "full immersion" method.

To me, the osmotic method looks pretty much like a normal pour-over method (except pouring only at the center) in which we usually called it percolation method.

Can you please help explain how percolation and Osmotic are different? or it is just the same thing?

thanks.

Answer 1

What's strange is that the post you link to describes full immersion as falling under the category of 'pour-over techniques'. Typically it's more common to think of two categories, percolation and immersion. Percolation covers everything involving water being pushed through a bed of coffee - so low-pressure percolation would be something like a Chemex or V60 pour-over, and a high-pressure percolation could be something like espresso. Meanwhile, immersion brewing covers French presses, cold brew, cupping preparation, Turkish coffee etc. where the coffee grounds sit in some water for a while, and then we use some method - the mesh in a French press or the steady hand of someone preparing Turkish coffee - to separate the grounds after. Some brewing methods blur the line between these two categories, like the Aeropress or the Clever dripper, which immerse coffee grounds in water for a period of time, and then use some mechanism to percolate the water through the grounds. Given all this, describing a 'full immersion' brew as a type of pour-over method is... weird.

It seems like what the linked post describes as a 'full immersion' pour-over is essentially a bad or failed pour-over. In a pour-over, what we want to do is have a steady flow of water through the bed of coffee, and we use things like water temperature, brew time, grind size, grind dose, etc. to control the level of extraction in our brew. Too little extraction means a dull, boring cup of coffee; too much extraction can produce lots of bitterness or acidity or nasty flavours in the cup.

Sometimes in a pour-over brew, for whatever reason - perhaps the grinds were too fine and clogged the filter paper, or perhaps the filter stuck to the brewing vessel and created a vacuum - the brew will stall and fail to draw down like it normally would. This increases our brew time and can lead to over-extraction with lots of bitter notes - which the post describes as 'unpleasant taste components'. It seems like this 'Osmotic Flow' is basically a bunch of tips for avoiding a stalled pour-over brew: try not to disturb the bed of coffee too much with rapid or heavy pouring, use a bloom phase, pour in batches instead of all at once, and so on. All good tips - but certainly not a new brewing method.

In short, then: percolation is one of the two main families of brew methods, alongside immersion brewing. A sub-category of percolation are pour-over methods - things like the V60, Chemex, etc. This 'Osmotic Flow' method doesn't seem to be a method at all; instead, it's a set of tips for how to have a good pour-over and avoid the common problem of a stalled brew. Helpful - but not a new method!

Answer 2

Osmotic brewing is so named because the process attempts to create a semipermeable membrane between coffee grounds and water via the pour pattern. That membrane is what facilitates osmosis.

A percolator, on the other hand, relies on immersion to brew. Water is heated in the sealed lower chamber and converted to steam. Pressure builds until enough pressure is reached to push steam up into the brew basket at top. There, the steam mixes with coffee and condenses, and brewing occurs. When enough water reaches the upper chamber, coffee brew drips back down to the lower chamber, where the water content can be converted back to steam to support indefinite brewing.

So, nutshell, osmotic pressure brewing tries to use osmosis for its extraction mechanism, while percolation uses immersion and heat.