True. I do a NSEW wiggle while applying tamping pressure and it seems to seal the puck much better. Concentrating force at an angle is probably more effective than straight down, I'd imagine, since the force of a straight down tamp would be transferred over the entire surface of the tamper where as tamping on an angle applies the force only on the area of the edge so the force would be greater. Still, according to the findings in Mark's article, tamping with any method or pressure will only compact the grinds so far in a full basket.

I mean if such a low amount of tamping force, 18lbs I believe, is needed to compact grinds for extraction if you tamp continuously as the basket fills then conversely if you can't generate enough pressure with 50 lbs to out do an 18 lb continuous tamp then the 50 lb tamp can't be compacting much of the lower portion of the basket. Intuitively I agree with the articles conclusion and to me it really highlights how dosing and distributing is probably more important than the tamp if you're tamping after filling the basket. Without the know how and equipment to do controlled testing I could never prove anything but from watching extractions and trying to figure out what's going on what I see supports the idea that there's not much compacting going on in the lower portion of the basket.

I guess the next level of control in extraction would be finding a method to ensure even density through the entire volume of the puck from bottom to top or testing how even density extractions compares to varying density extractions shot quality wise.

mrgnomer wrote:I guess the next level of control in extraction would be finding a method to ensure even density through the entire volume of the puck from bottom to top or testing how even density extractions compares to varying density extractions shot quality wise.

I don't assume that perfectly uniform compaction will mean better extractions, although I have noted many assume uniformity is goodness (e.g., brew temperature, pressure, and now compaction). To look at it another way, no pro barista worries they'll be spanked by a Swift grinder, which arguably has more uniform compaction than any (manual) non-layered compression technique.

For me, it makes intuitive sense that reduced density nearing the exit would result in an overall more even flow rate (but I'm not a physics major or fluid dynamics engineer). I'll bring this up next time I see Bob Barazza, he'll surely have an informed opinion.

I'm not sure- how does espresso extract under pressure? It seems to extract from the edges in and from top to bottom. If that's the case it would explain why the first bit of the extraction is dark and dribbles around the center then starts to concentrate to the center, quicken then lighten up. Density at the top of the puck and around the edges would be greater where the extraction seems to start and lower as the extraction works its way in and down. Wouldn't an evenly dense puck extract longer and better given that the rate of extraction/pressure would stay more constant than a puck who's density varied from top to bottom? I don't know, though.

mrgnomer wrote:Wouldn't an evenly dense puck extract longer and better given that the rate of extraction/pressure would stay more constant than a puck who's density varied from top to bottom? I don't know, though.

Me neither, but here's my layman's thinking: Imagine a copper pipe under pressure with no obstructions. Now bisect it with a porous filter (e.g., a snubber). I would expect the pressure downstream of the porous filter to be lower than the upstream pressure. Now add a second porous filter after the first. The pressure would be highest before the first filter and step down after each filter. Back to our coffee puck, assuming that the amount of solids extracted is proportional to (a) the pressure and (b) flow rate, I conclude that reduced density lower in the puck could be "a good thing" for more evenly distributed extraction pressures.

But it's midnight and I'm exhausted, so take it with a bag of rock salt. Maybe I can convince Lino to machine a basket that can be installed in either orientation (i.e., tamper compression side up or down) and see if it makes a difference in the cup.

Yeah, it was getting late last night. A little late to be thinking about that kind of stuff.

I think your porous analogy makes sense. One thing, though with the pipe there's no back pressure after the filters. In a basket there's the holes of the basket adding some back pressure, I'd imagine, making it possible for the upstream and downstream pressure to stablize. Ultimately even extraction throughout the entire puck could be the goal, I guess. Might differences in puck density lead to different extractions? I mean increased density would result in higher pressure/extraction where as decreased density would mean lower pressure/less extraction. I think I understand your reasoning with the higher density more extraction, lower density less extraction evening out extraction pressure throughout but I still think changes in density might lead to changes in extraction.

Just when you thought espresso couldn't get more controversial or exciting

I just tried evenly distributing and lightly tamping a 1/3 filled double basket then finishing the dose, distribution tamp with a total volume of about 18g. The distribution for the top of the basket was well under the rim so I used my thumb for the Stockfleth's move and tamped normally. The shot poured thick longer and the cup was deeper and more intense. There might be something to compacting the grinds right down to the bottom of the basket- maybe.

HB wrote: this may also explain why Michael Teahan's SCAA presentation reported no significant difference between a 30 and 300 pound tamp.

Ehm, (true confession time) when I'm in a hurry and the last dose of grinds out of the grinder (usually my shots) is a little light, I might just get out the beans and grind and re-clean the grinder and have the whole process wait, or, like today when I was just out of beans when the dose was light, I might just redouble my efforts on the tamp and hope that it works out to be drinkable. While the shot blonded a bit earlier than a whole dose would have, I did get a nice near-double (about the amount you'd get out of a ristretto) that tasted better than just adequate, it was good, in about twenty seconds.
Now, if I hadn't changed the tamp from my usual thirty to about forty-five (just a guess) I'm sure that this one would have been a gusher. I also know that if I over-tamp my normal dose, it'll take forty-five to fifty seconds before blonding. Am I the only one, or have I misunderstood the statement that there is "no significant difference between a 30 and 300 pound tamp".

Interesting. So if I took the piston off of my tamper, took my dosed basket back to maintenance and used the hydraulic press to smash the coffee down to 300psi, I would have no negligible difference in the percolation I normally get with a 60lb tamp?

Maybe true but I am having a hard time taking that statement at face value.

cannonfodder wrote:Interesting. So if I took the piston off of my tamper, took my dosed basket back to maintenance and used the hydraulic press to smash the coffee down to 300psi, I would have no negligible difference in the percolation I normally get with a 60lb tamp?

Eagerly awaiting the results...

I may try it.

Psyd wrote:I also know that if I over-tamp my normal dose, it'll take forty-five to fifty seconds before blonding. Am I the only one, or have I misunderstood the statement that there is "no significant difference between a 30 and 300 pound tamp".

You understood Michael's claim correctly, and I am equally dubious. Like you, I admit to "modulating" tamper pressure in an emergency, e.g., distracted by the kids, forget a required grinder adjustment for the next shot, and have one minute before flying out the door. I didn't press (ha!) Michael on the point when he brought it up in conversation while leafing through his presentation, but I have to assume there's another factor he didn't mention.

It doesn't surprise me there's some point at which further uni-directional pressure makes little or no difference... that was Lino's point about nutating action and asphalt compression.