roastini wrote:I think your latter point - that the puck could have been more fully compressed for that flow rate - is really what Scott is getting at. I took his point to be that once the puck has gotten as compressed as it's going to get, you would expect that the pressure needed to maintain a given flow rate would decrease over time, due to puck erosion. But his point (as I take it) is that the puck was still compressing, the pressure thus needed to increase to counter the effect of that compression, and that necessary increase more than offset the effect of the puck erosion.

That is a good point about puck erosion. It would be nice to see the pressure level out and start decreasing even if it led to a bad shot. It would also be nice to explore how puck erosion affects the relationship between pressure in general, flow rate, and fully-compressed pressure for a given flow rate. Thanks for your comments.

AssafL wrote:I (obviously this is interchangeable: for a given puck, a certain pressure will yield a flow. Similarly forcing the flow would mean that the pressure across the puck would be the same pressure as before. Conservation of energy or work in this case).

I think that it would be interesting to consider conservation of energy, momentum, and mass across the height of the puck to gain insight into the interplay of pressure, flow, and temperature. The model would have to account for compression of the puck and erosion of solids. Head losses such as the flow through the holes at the bottom of a portafilter would also have to be considered. The model would have to be flexible enough to account for different types of grinds and espresso.

On the other hand, I do not think that the pressure has to necessarily drop once it has leveled off for a given flow rate. For example, if the initial rise in pressure is gradual enough, the extraction of solids (erosion) could occur before or as the pressure levels off when the puck is fully compressed for a given flow rate. For the purposes of flow modeling and possibly bounding the problem, we could define leveling-off pressures for pucks that have no erosion with no extraction of solids and pucks that are fully eroded with full extraction of solids. The pucks will compress differently for these two limiting cases.

Puck erosion should continue throughout the shot. If puck erosion ceases, that means you're not extracting anything, which raises the question of why you are continuing the shot.

And whatever is in the cup is over-extracted swill.

roastini wrote:Puck erosion should continue throughout the shot. If puck erosion ceases, that means you're not extracting anything, which raises the question of why you are continuing the shot.

Thank you for the education. I feel like I am being fed by a firehose. I am keen to bound the problem, regardless of the swill that ends up in the cup. If the 1.5 ml/s flow rate is varied +/-10%, what relative change in pressure would you expect in the peak pressure when it levels out just before it decreases? Given the flow rate into the puck and an accurate weight scale, it seems possible to measure a rate of erosion. How uniform do you expect the rate of erosion to be? I think that it is interesting that a Decent Espresso machine provides the opportunity to explore the physics of espresso making. Thanks again for your insights.

Here's a short video Jasper Coffee took of yesterday's DE1+ demo with Scott Rao in Budapest. Best coffee shots so far on this machine, but that's because it was Scott's own Kenyan roast beans. Both the flow profile at 2.2 ml/s and a 9-bar-flat shot delivered good (but different) results.

https://www.facebook.com/jaspercoffee.m ... 847650013/

and meanwhile in Hong Kong, we're taking over 3000 sq ft (about 300 sq meters) of new space next door, to dedicate it to manufacturing, because our first space space (R&D, accessories, lunch!) is now crammed full.
I'm following the discussion here regarding puck erosion & etc. Lots of savvy people here giving good answers so I don't feel like I need to add more. In about 2 months, some of those clever people will have their own DE1+ and will be able to say much more, and my unfair advantage of being the only DE1+ owner, thus who can see this stuff, will come to an end!

decent_espresso wrote:Here's a short video Jasper Coffee took of yesterday's DE1+ demo with Scott Rao in Budapest. Best coffee shots so far on this machine, but that's because it was Scott's own Kenyan roast beans. Both the flow profile at 2.2 ml/s and a 9-bar-flat shot delivered good (but different) results.

https://www.facebook.com/jaspercoffee.m ... 847650013/

One quote in particular was very interesting - and it was about flow profiling that resulted in pressure dropping for a light roast - and specifically - that if you would have kept pressure the same - the shot would have become very acidic (i.e. under extracted).

To many here (and especially the Slayer crowd) the common consensus is that grinding finer allows one to extract high enough to avoid the acidity of under extraction (of course given enough PI time to allow flow). This is at given Slayer/LM standard pressures (so anywhere from 7-9bars depending on PWM setting).

What seems to be suggested is an alternative to the Slayer extraction for light roasts - that one can grind normally (not excessively fine), eschew Slayer PI and even start the pull at a normal pressure - and then achieve ample extraction given a severely decaying pressure profile? (probably more decayed than a Slayer's constant PWM and a Lever's spring decay can provide)?

Did I understand that correctly?

I am not suggesting doing this with PP - obviously the controllable way to do this is to set a low enough flow rate profile and let the processor make the necessary adjustments to the pump. But the extraction suggested is intriguing.

AssafL wrote: What seems to be suggested is an alternative to the Slayer extraction for light roasts - that one can grind normally (not excessively fine), eschew Slayer PI and even start the pull at a normal pressure - and then achieve ample extraction given a severely decaying pressure profile? (probably more decayed than a Slayer's constant PWM and a Lever's spring decay can provide)?

WIth a spring lever in particular, you can emulate this "severe crash" in pressure by holding back the lever as it is on its way back up to keep the flow rate where you want it. another_jim for example does this on pretty much every shot. Having tried a Panama Elida natural pulled both by Jim on his lever and on a Slayer (on the same day, but not back to back) I can say that the technique is certainly effective. I have taken to doing this sort of shot style myself much more frequently than I used to.

AssafL wrote:What seems to be suggested is an alternative to the Slayer extraction for light roasts - that one can grind normally (not excessively fine), eschew Slayer PI and even start the pull at a normal pressure - and then achieve ample extraction given a severely decaying pressure profile? (probably more decayed than a Slayer's constant PWM and a Lever's spring decay can provide)? Did I understand that correctly?

With a coarse grind of a light roast, we're seeing pressure drop hugely, from 9 bar to 2 bar, over 25 seconds, in order for the DE1+ to maintain a constant flow rate.

At a fast (2.5) flow rate, the drop in pressure has been greatest. Roll back to 2.2 ml/s and we're seeing 9->4 bar. Slow down to 1.8 ml/s and it's more like 9->7 bar. Always with a ~27s shot.

This is only my experience so far on tour of France and at Budapest with Scott, always at 3rd wave coffee shops where the roasts are light.

If one doesn't have flow profiling, but one has pressure profiling, then a sharply decreasing pressure profile and a coarse grind, would make good coffee.

Finer grinding, but still light roasts, made less tasty coffee (and 32s to 42s shot durations) and much less steep pressure curves during flow profiling.