HB wrote:See FINALLY! Transparent portafilter espresso extraction videos to see this in action.

I don't know if this was to support me or contradict me, but you can perfectly see that even for a total uneven surface, the water flows parallel to the surface. That is exactly what we want for an unleveled machine, since this means the puck will saturate evenly with water.

I find it interesting in those videos, that both extractions have the same off-center left flow from the puck. I would have expected it from the angled puck, but not the level puck.

Also, I'd love to see this re-ran with a less extreme angle. Let's see 1-3 degrees, something one might experience naturally, not this 15 degree exaggerated pull.

Pflunz wrote:Hi, I did the math. At a 5° angle, the vertical force from gravity is only ~10^-5 of the vertical force by pressure. So when the water flows through the 12mm thick puck, it will be shifted 0.1µm to the side.

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OK, assuming your assumptions are correct about flow through the puck...e.g. that water flow through coffee grounds is unaffected by things like capillary forces and surface tension, what occurs in your model during e-61 pre-infusion in those several seconds as the pressure builds from zero to 4bar and then up to pump pressure (say 9bar) as the infusion chamber spring opens? I think that is enough time for the puck to soak lop-sidedly and you may in fact see this in a bottomless portafilter extraction with a tilted machine.

In any case I agree that normally a bit of tilt is not going to cause channeling, though it might if there is asymmetry in the initial puck wetting during pre-infusion in machines, like those with e61 groups, that allow for pre-infusion.

I think the most noticeable effect will be when the espresso coming out of the filter joins up into a single stream that the stream may be formed up on one side instead of the center.