VST basket size and grind volume are at odds - Page 3

Beginner and pro baristas share tips and tricks for making espresso.
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#21: Post by cafeIKE »

RapidCoffee wrote:cafeIKE wrote:
Tamping has next to ZERO effect on flow.
Have you actually tested this?
About 15 years ago, when Schomer mandated 30 pound tamps and every new roast since that misbehaves. I'd guess my tamps are on the low side of 10 and I'll try a heavier occasionally, just like a different basket or tamper face for a recalcitrant coffee.

Poor distribution may benefit from increased tamp pressure and / or nutation, but I've not found the benefit.

I confess that I seldom - maybe twice a year - look at the bottom of the PF. If the shot streams down the middle of the group, doesn't fall apart too soon and the shot tastes well, I'm good.

Maybe I'm just lucky?

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#22: Post by RapidCoffee »

cafeIKE wrote:Poor distribution may benefit from increased tamp pressure and / or nutation, but I've not found the benefit.
I'm confident that my puck prep is solid, and this is not a consequence of poor distribution. Again: try comparing no-tamp and 30# (or even 10#) tamp extractions, keeping all else constant. I believe you'll observe a significant difference in flow, at least with classic 9 bar espresso shots.

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#23: Post by cafeIKE »

I'm not questioning anyone's puck prep.

It's simple math. 120psi x 23¾ in² ≈ 2850 120psi x 4 in² = 480 pounds of pressure.
A tamp of 30 pounds / 23¾ in² = 0.01 30 pounds /480 = .06psi. Tamp pressure is a rounding error.

I asked back in ought eight How important is tamping?. Today I redid the 'speriment with a bit more precision.

Coffee: 18.01g* Sterling Blendo Stupendo
25±0.5s from pump on. 33±0.5g out. Probably a few seconds delta between pump off and photo.

One image is tamper placed on puck to ensure screen clearance and the other is a handstand. The handstand was a tad less enjoyable, but there are myriad uncontrolled factors that could contribute to the taste delta. The delta was no more than back to backs sampled in our finer emporia.

* pure luck for identical doses
early morning math errors


#24: Post by jpender »

cafeIKE wrote:It's simple math. 120psi x 23¾ in² ≈ 2850 pounds of pressure.
A tamp of 30 pounds / 23¾ in² = 0.01psi. Tamp pressure is a rounding error.
The math is apparently not simple enough. A 58mm portafilter is roughly 4 in². And force is not pressure.

That minor bit of confusion aside, it's true that normal espresso pressures are far greater than tamping pressure (less than 0.5bar). But that's oversimplifying what is going on. Even in the video link you posted that supposedly demonstrates how pucks are compressed during extraction the author of that video says: "The last shot has the same dose, grind & pressure but light tamp and it's not so good. So tamping seems important." And in the video comments he adds: "Also, it seems a firm and level tamp helps a lot to get a delicious extraction, at least in this test setup."

It probably depends on the details of the machine, the way it's operated, and other factors. You can't just pull a few shots and conclude that tamping is important or not.

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#25: Post by cafeIKE »

I stupidly typed PI in the µSoft calculator instead of just P. Too early for me to do complex math :oops:

No argument on a consistent level tamp. A specified pressure is swamped by other parameters. Drop a dose by ¼g and no amount of increased pressure will restore the shot parameters.


#26: Post by GDM528 »

Has anyone run a grind size analysis pre and post tamp? Grind/measure/tamp/dump/measure. Using one of those fancy-pants computerized systems.

Does tamping hard, as if you're trying to push the grinds into another universe while screaming like an Olympic weightlifter, fracture the larger particles?


#27: Post by jpender » replying to GDM528 »

Laser diffraction? No. But I was attempting to measure tamped espresso grind bulk density and decided to test how repeatable my method was by re-tamping the same grounds over and over. That is, I ground, tamped, measured, dug the grounds out, put them back and retamped, remeasured, etc. I only did this for two samples and then gave up because it was clear I wasn't getting the same numbers. But there did seem to be a trend toward higher density with multiple iterations. So it's possible that tamping results in irreversible changes to the grounds.

Not enough to prove anything, not even close. But maybe a hint at something going on.

Or maybe not.

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#28: Post by ira »

I wouldn't expect any tamping pressure you can apply to be able to fracture anything unless there is a long skinny particle placed so any movement will fracture it. As I thought about this, I came up with this test. Put one layer of beans in a portafilter, tamp as hard as you can. Did any break? If so level and repeat till they stop breaking. I'm going to guess you can get past 3 or 4 passes. Not sure what it means, but I would infer if my assumption is correct that tamping pressure has no effect.

So I decided to try this but the problem with proper tampers is the won't go down far enough in the basket and all my cheap tampers are at the shop so I found a washer from my crimping press and used that. While it's really far from what an actual tamper would present, and it took many tries to get to this consistency, at about this point coffee was about the point where it seemed to stop fracturing. I'd guess if I'd had something that covered all the beans, smaller tamper, it would have stopped sooner.


#29: Post by jpender »

HB member @crwper has been investigating espresso grinds recently. He found the same thing that I did, that repeated tamping increased the density. He has better data than I do.

This is a graph of 9 samples tamped repeatedly, at three different tamping forces. The force was constant for a particular sample.

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#30: Post by ira »

I would guess that repeated tamping might increase density, but that wasn't the question, he asked if tamping hard would cause the grounds to fracture and get smaller.