peacecup wrote:It seems to me that a non-compacted mass (ie light tamp) would be very unstable when first exposed to the brew water, and that the surface layers at least would be disturbed. I've always assumed that this would lead to channels being formed in the "puck", causing an uneven extraction. A firmly-tamped a polished surface would act as a buffer, allowing the puck to remain intact while water slowly infuses it. Think of an earthen dam being hit by water, for example, vs. the same pile of earth that was not compacted.

I don't fully agree with this theory. IF the "puck" is evenly distributed and the water pressure evenly applied, there should be little-to-no disturbance to the puck regardless of the compactness of the grounds (so long as there is constant forward force on the puck). The basket is the barrier and the grounds are held back by it. As more pressure is applied, the puck will become more compact against the basket screen and thus provide more resistance against the flow (think leaves packed in a drainage grate). You should get channeling if there is a void of grounds in the puck and/or jet(s) of water against it, otherwise it should stay intact. If there are voids, it would also make sense to me that a lesser tamped puck and slower ramp-up of force would allow the voids to fill-in and basically somewhat heal, resulting in a better overall extraction. I believe I read a thread on here where it was brought up that increasing the force on the lever tended to slow the extraction and that makes sense with the water force compressing/compacting the puck.

I don't use a lever machine (yet) but lately I've been experimenting with a little bit different technique: Grind enough to cover the bottom of the basket, very lightly tamp with a smaller tamper that fits the bottom of the basket, finish grinding to fill the basket and lightly tamp the top. The jury is still out...

'Q' wrote:As more pressure is applied, the puck will become more compact against the basket screen and thus provide more resistance against the flow (think leaves packed in a drainage grate).

Also, as with dry leaves to wet, the wetted coffee grounds swell together in the confines of the basket, filling voids, then are compressed with water pressure. (I'm no scientist.)

With a hard tamp, which I of course think makes great espresso, the outside puck surfaces are surely tamped more compact than the interior.

AndyS wrote:...I've repeatedly compared shots tamped at 10 lbs with shots tamped at 60 lbs and found little or no difference.

By 'light tamp', I am talking about 0-300g, i.e. less than 1 pound ... not 10 pounds. The very light tamp just creates minimal headroom, to keep the shower-screen clean.



Regards
Timo

peacecup wrote:Dan's assertion that the puck becomes a slurry during multiple pulls, this is not always so. With moderate (~10#) tamp on the Ponte Vecchio the puck will remain entirely intact during two or more pulls if the dose if the grind is relatively coarse and the basket full (but not necessarily touching the screen).

For the record, I am not asserting anything. I assume the puck has slurry characteristics because the vacuum created by the upstroke doesn't produce catastrophic channeling as I would have expected for a firm puck. An assumption is all I can offer since I have not measured or observed the process directly.

peacecup wrote:I can say this for certain because there is no way that the solid pucks I eject from my double basket could be compacted by the piston pressure.

That sounds like an assertion of an assumption to me, but I'm nitpicking. From this point forward I will focus on the end results in the cup and not "puckology."

This is all very interesting in theory, but as Dan notes, it is results in the cup that count. That said, it would be satisfying to understand the mechanisms that determine results. In this thread I am encouraging fellow HB'ers to experiment with different techniques, to try to shed some light on how tamp pressure (and related changes in grind and dose) effect flavor, crema, shot volume, or whatever else they consider an important result. For example, we've seen timo expound on the virtues of the "tampless tamp". I would like him to try dialing in a hard tamp, then have him describe HOW the results in the cup differ.

Of course, it is an assumption that a firmly-tamped puck will stay intact, since I cannot actually see it. And it is somewhat trivial "puckology" on one level. On another level, however, understanding what happens in the basket can increase our ability to predict what comes out the other end. This is one reason naked PF's are so popular, because they give us a glimpse, at least, of what we can't see inside.

After 20 years of schooling and working, I am slowly beginning to consider myself a scientist. I like to uncover the mechanisms that underlie patterns that I observe. One simple example is "What did I do to those coffee grinds to make the espresso sweet (or bitter!)?".

One of the reasons I love espresso so much is that it is the interaction of a few simple physical factors (pressure, temperature, hydrodynamic properties), can make one of the "Seeds of the Earth" even more pleasurable than it is when simply boiled.

BTW, this AM's cappa was set to a coarser grind/harder tamp than I have been using lately, and it was exquisite. More food for thought, until have some time this weekend to run some simple taste tests...

PC

HB wrote:For the record, I am not asserting anything. I assume the puck has slurry characteristics because the vacuum created by the upstroke doesn't produce catastrophic channeling as I would have expected for a firm puck.

As a non-scientist, I have been pondering the vacuum phenomenon in the piston chamber, and just how disruptive or significant it could be. With the Lusso, let's assume pressure on the saturated puck. The arm is then lowered to raise the piston, creating the vacuum whose forces increase as the piston lifts-but the piston on this machine lifts only about 5/8 inch in total. Methodical movements would limit the potential shock effect. And somewhere before that time water pressure from the boiler fills the vacuum.

In thinking about this thread in the shower this morning (I do some of my best thinking in the shower ) I came to a couple more theoretical conclusions.

1) Assuming acceptable grind, the effect of tamp pressure is probably parabolic with respect to flow. A variance in tamp between 0# and (I would guess) about 10# affecting flow very little, if any. Tamps between 10# and roughly 40# would have greatest effect. And variances above 40# (within reason) would again be little. This also stands to reason that tamp pressure at either end of the scale would be easiest to maintain consistency.

2) Grind fineness and distribution would have greatest influence on flow rate at the no-tamp to light-tamp end of the scale.

I'm not advocating anything, just thinking aloud here. It does seem reasonable to me that one would be most consistent (but not necessarily the best tasting) by grinding coarser and tamping hard. Of course it seems that the best tastes come from that fine balance between grind, distribution, tamp, flow, temperature, etc, etc, et... (oh, and ones personal taste) so I really doubt there will ever be that magic answer.

peacecup wrote:... I can say this for certain because there is no way that the solid pucks I eject from my double basket could be compacted by the piston pressure. I see I need to post some photos of these.
...
PS, Andy, I do know Richard C, but mostly by reputation. He is a tireless advocate for preserving the last great wilderness in North America, the Tongass National Forest.

I know peacecup's pucks only by reputation, but I do often get firm pucks from the Cremina using no tamp whatsoever. I recall the edges of the Lusso's spent pucks being more Heraclitean. Differences in brew pressure are likely to be a major factor here, as well as dose to water-draw ratios.

Regards
Timo

I have a Lusso. I just prepared two baskets with a blend of beans representing two Brazils, one Nicaraguan, and one Ethiopian Sidamo, roasted FC+, aged four days.

For basket No.1 I ground to my standard for a very light tamp. For the next basket, No. 2, I ground one notch coarser (Macap M4), and prepared this with a 30 pound tamp. I pulled basket No. 1, tasted and enjoyed a full-bodied cup with delicate chocolate flavors and an overall rounded profile. Then I pulled basket No. 2-more effervescent body, and more biting chocolate, overall less balanced and smooth than No. 1. For both pulls, flow rates and volume were very similar. Lurking variables include temperature, moon and stars-no pretense of a scientific method, but representative of what happens at my espresso bar.

Over time, the light tamp works well for me, my blends and machine, and my tastes. It is fun to taste test both tamping methods. Every home barista is sure to find out what works best to produce the most pleasing cup.

'Q' wrote: IF the "puck" is evenly distributed and the water pressure evenly applied, there should be little-to-no disturbance to the puck regardless of the compactness of the grounds

That's a very big IF.

(1) The puck is never perfectly evenly distributed.
(2) Since water flow into the grouphead commences as single droplets, it is NOT evenly applied at the beginning, which is the most crucial time.