Will Chemex paper used for bottom filter lead to uneven espresso extraction? - Page 2

Beginner and pro baristas share tips and tricks for making espresso.

#11: Post by GDM528 »

Well, what I can't stop seeing, is this:

(full disclosure: didn't get any immediate hits from a web search, so I used DALL-E to generate the image)

But seriously, the dot pattern from the holes in the basket look pretty similar shade and evenly cover the full pattern, so I think that implies a pretty uniform extraction. The Rorschach-y blotch near the center is probably just from the last drops of espresso outside the basket getting sucked back up into the puck when the 3-way valve is opened - or perhaps it's a ghost image of the critter that was climbing around the coffee plant you're drinking from ;)

You might be able to test the paper's ability to show channeling, by deliberately creating one to see what it looks like: use a toothpick to poke a hole from top to bottom of the tamped puck before pulling the shot. I wouldn't suggest doing that with a roast that deverses better treatment, but one way to find the edge of a cliff is by driving off of it.

Just a theory: the paper inserts a thin, non-soluble membrane in the path of the fluid, kinda like a basket with a gazillion holes, which creates a short, lateral flow as the fluid directs into the actual basket holes. That lateral flow may create a more uniform distribution of flow and pressure, leading to multiple streams. The bottom of my VST basket is slightly bowed, so eventually my streams coalesce, roughly at the 1:1 brew ratio mark.

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#12: Post by yakster »

Keep in mind that the Chemex paper has thicker and thinner areas, it's not perfectly uniform. See 2:00 in this video for a microscopic examination of Chemex filter paper dry and wet.

LMWDP # 272