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Tamping Science, Theory and Practice, Part One by Mark Prince
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MarkPrince
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Posted Fri Oct 13, 2006, 4:53pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

DavidMLewis Said:

Hi Mark,

Nice work. I think I personally learned a lot from Chris Tacy's insistence that distribution was critical, and that what you were trying to do with the tamp was not mess it up. I.e. if the distribution isn't even, the tamp can't fix it. I'd go a bit further: on the rare occasions when I get channeling these days, it's almost always because my hand has moved at the end of the tamp, so that the angle of the tamper face changes and the tamped surface moves. This seems to break it free from the basket wall.

One technique I've lately adopted that seems to help a bit is to put the tamper flat on the counter with my arm vertical before I tamp. This makes sure my arm "knows" what the proper alignment feels like. After I've pulled the shot, I'll also look at the top surface of the puck. Since I know the puck face was horizontal when it went in (the lines on the Ergo-Packer, as you know, are a good check), if it's not horizontal after it swells into the screen and then subsides, it can only be because my distribution wasn't even.

Posted October 13, 2006 link

Great stuff....

One of the quandries (sp?) for me in this article was whether or not to just print the entired darned thing (which got over 10,000 words at one point), or to break it up. The article (now down to about 7,500 words but growing again) just seemed too much to do in one go, and imo, a lot of crucial things might get lost as or interpreted as minutia if I posted the entire thing, so I decided to break it up, and in part two, I talk a lot more about what happened pre-and immediately post naked PF "revolution".

I also mention distribution and levelling a bit, but never without getting into detail - I stress a lot that these topics are so important, they deserve their own articles. In 3, which I'm still re-writing as feedback comes in from folks on some of my discussion points, I push that point even further - basically it's a call out to anyone who wants to tackle the idea of dose, distribution and levelling as its own article, or series of articles. It's taken me about 2 years to write this tamping opus... and much of it is just my own BS and guestimations and imagination running wild - some with some real empirical testing to back it up, some with just out of the box thinking about things. I haven't even started to write anything more concise and specific about distribution and levelling, but just like tamping, it's something I've spent a helluva lot of time thinking about and working with.

Today, the topic came up in a phone call about grinders and what Baristas want in a good grinder. It was a good debate and there's minor (very minor) disagreement between the three people on the phone about what's most important - but I think we all agreed that the initial dose and distribution of the grounds is paramount to starting off a good shot build (accepting the fact that you have good coffee and a good grinder to begin with).

Mark

 
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edwa
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Posted Sun Oct 15, 2006, 12:33pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

Mark, your article and the resulting comments have been a wealthy feast of information to feed my continuing education.

After purchasing a naked portafilter (NPF) for my finicky Miss Silvia I discovered how much I needed to work on my technique.

-I've bought a thermocoupler and snaked it from a bottom spout to inside an empty potafilter and then timed various temps from when the boiler light turns OFF.
-I have a bathroom scale on my counter and use it.
-I've stopped using any taps/knocks of any kind and have started to get more consistent results using the WDT (Weiss Distribution Technique). Still I get little errant jets that spray off to one side or the other.
-I've seen how much difference a blend can make by purchasing Intellegensia's Black Cat. I saw picture perfect crema, properly behaving NPF flow (for the most part), thick mouthfeel, BUT not being a big chocolate fan I won't stick with it. I want more nutty, caramel, creamy - besides the point.

Back to the topic:

After reading about how the Swift grinder tamping worked, I can see how the "pipe" analogy came up. It does lead to the question, "Why not a basket fill in 3 stages". I gave it a try. In the back of a drawer I found the small plastic tamp that came with Silvia and saw that it fit all the way to the bottom of the LM double basket. Dialed in a grind for a WDT pull and then using the same grind setting I filled approx a third of a basket and did a spin without exerting additional pressure. Same process for the second third. Finally, on the last I levelled and tamped with my 58 mm flat bottom via Staub technique with 30 lbs. Overfill. The NPF was stiffer to lock in and had a big divot for the dispersion screen screw. Dumped it all and started again, this time with more headspace room.

Now, I'll have to continue with this process to see how it averages out but this first pull, blonded too quickly. BUT, I didn't have any of those channeling jets making a mess and the stripping did not twist to a barber pole. It certainly is worth trying again.

If you're taking any requests for Part 3, mine would be some illumination on the actual gripping of the tamp. After studying the photos from HB's Tamp Road show I've played around with different grips seeing how they can cause different pressure points and thus have modified my own approach.

Lastly, I imagine the process will have to adapt with the type of machine being used, say a Silvia to a Hx machine. I'm probably wrong on this but no matter how hard I try to nail the temperature I always feel that I'm battling the force of water the Silvia puts out. You fed this suspicion by writing:

a) many machines are based on the e61 design, which I will argue requires less care about tamping than non-e61 machines.
b) historically, tamping was not seen being crucial for espresso, especially pre-9BAR brewing - and for the same reason why it's less crucial on e61 machines (the very slow, gradual build up of water at neutral or line-feed pressure, then at around 7 seconds, a jump to 9bar), these machines barely passed 1.5BAR in pressure throwing water at the ground coffee.

Thank you for the 2+ years you've already put into this.
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cv
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Posted Mon Oct 16, 2006, 6:00pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

I'm just a newcomer to the world of good coffee and to coffeegeek, but I have been literally glued to your site for the last 3 days and I'm sure it has saved me a year of futzing around and drinking really bad home made shots. I can feel an obsession coming on. Can't wait for the rest of the article!

One thing in your terminology that confused me for a while (physics major, unfortunately) but I think I have it down now. You are talking 30 lbs of tamping 'force' not pressure, are you not? Pressure is applied to the grounds with the tamper but if I do the math 30lbs/square inch pressure on a 58mm tamper (roughly 3.14 sq inches) would require a little over 94 lbs of force. I'm still not exactly sure what 30 lbs of force feels like but I am working on it! And then I can concentrate on the other subtleties.

I hope I am not being a nitpicker and I'm not trying to be a smartass. And I'm hoping you might be able to give me the name of a few places in the West side of Vancouver where I can buy a good shot to see what I should be aspiring to. If it's not appropriate to list them in a reply on the site, please contact me privately.
Thanks a bunch!
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conerad
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Posted Mon Oct 16, 2006, 11:15pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

so it seems like one of the biggest problems with the way most of us tamp is that there is little to no pressure on the bottom third of the puck. i understand that this is because the pressure has pretty much been dispersed by that level. i also understand that this is due to the grinds not being aligned or interlocked properly. this is why people knock the portafilter? to settle/align the grinds?

perhaps a less violent method would give the benefits without the risk of losing the seal around the sides of the puck?

how about distribution while the pf was resting on a vibrating surface?

i can't thing of what you'd use offhand, but someone's gotta have some kitchen appliance in a cafe setting that rattles/vibrates like crazy.
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MarkPrince
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Posted Tue Oct 17, 2006, 12:49am
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

cv Said:

I'm just a newcomer to the world of good coffee and to coffeegeek, but I have been literally glued to your site for the last 3 days and I'm sure it has saved me a year of futzing around and drinking really bad home made shots. I can feel an obsession coming on. Can't wait for the rest of the article!

Posted October 16, 2006 link

Woot - another Vancouverite in the mix - hey, if you're interested, make sure you fire off an email to me at coffeekid at gmail dot com and asked to be added to the "invite" list I have on evite.com for cupping events, tastings, podcasts, etc.

I haven't sent one out in a while, but I'm way overdue for doing another cupping event with some CoE coffees.

cv Said:

One thing in your terminology that confused me for a while (physics major, unfortunately) but I think I have it down now. You are talking 30 lbs of tamping 'force' not pressure, are you not? Pressure is applied to the grounds with the tamper but if I do the math 30lbs/square inch pressure on a 58mm tamper (roughly 3.14 sq inches) would require a little over 94 lbs of force. I'm still not exactly sure what 30 lbs of force feels like but I am working on it! And then I can concentrate on the other subtleties.

Posted October 16, 2006 link

Uh oh.

People don't know this, but I flunked Gr. 10 Physics (well, flunked it because I managed to get the teacher to hop over his desk and threaten me, and I was removed from the class for the rest of the year, but that's another story).

But, back on track, when we (as in I guess the entire espresso-lovin', barista community) talk about tamping with 30lbs of pressure, the way most of us figured it out was loading up a portafilter, putting it on a bathroom scale, and pressing down with a tamper till we saw 30lbs registered on the scale.

Also, there's devices that can also do this - the amazing espro tamper has an internal spring preset to 30lbs of downward pressure. And I hope to get a "clickmat" soon from Lars at Xpressivo which does something similar, but with a tamping "mat" instead of the tamper itself.


cv Said:

I hope I am not being a nitpicker and I'm not trying to be a smartass. And I'm hoping you might be able to give me the name of a few places in the West side of Vancouver where I can buy a good shot to see what I should be aspiring to. If it's not appropriate to list them in a reply on the site, please contact me privately.
Thanks a bunch!

Posted October 16, 2006 link

No nitpicker at all - in fact, I could use the help and analysis of someone studying physics - all my "science" is empirical - just basically observation, guesstimation, and what little common sense I have.

Re cafes: west side - well the obvious is Elysian Room (5th and Burrard) and Wicked Cafe (7th and Hemlock). Towards UBC, it's always been a kinda wasteland, but I have vague recollections of someone at the Western Regional Barista Competition this year in Vancouver saying something about a decent shop opening up recently - but I can't recall where.

If you go post in the Western Canadian forums here on CG your question, maybe the person who told me will read it and chime in.

Mark

 
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Posted Wed Oct 18, 2006, 1:41pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

So we got a phycisist here, but the solution comes from something chemists are more familiar with:
Tamping is a subject with long history and practical research in the field of explosives.  Powdered/crystalline explosives are almost always tamped into blasting caps in sections.

How is this best applied here?  It's easy, no need to take a bunch of core samples from the puck and infinite adjustments.  Simply add some coffee, flatten it, and tamp it, then some more, and so on.  Three or even only two sections are sufficient.  Technically, you would get most even compression through the depth if each higher layer is slightly thinner than the previous one (since the lower layers get some of the tamping pressure from tamping the upper ones -- this matters because, although only maximum pressure reached would matter if the coffee reached a static equilibrium after each tamp, this doesn't happen in practice as the irregularly shaped grounds will change orientation and still move a bit in a lower pressure tamp after a higher pressure one).  Instead of decreasing layer thickness, you can slightly increase tamping pressure for upper layers, or do both

What I do: I put about 60% of the grounds in the basket, flatten them, tamp with 20 lbs weight on the tamper, then put the rest 40% in and tamp with 30 lbs.  If you really want to mess around, you can try a three-part 40%-35%-30%, 20-25-30 lbs process, but it's extra effort with diminishing returns (I can't tell much of a difference in puck compactness).
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Posted Wed Oct 18, 2006, 1:59pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

I am no phycisist nor chemist but... when the hot water hits the puck, why doesn't all this equalize when the grains swell and fill all the available space ?

 
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MarkPrince
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Posted Wed Oct 18, 2006, 2:22pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

Prune Said:

How is this best applied here?  It's easy, no need to take a bunch of core samples from the puck and infinite adjustments.  Simply add some coffee, flatten it, and tamp it, then some more, and so on.  Three or even only two sections are sufficient.  Technically, you would get most even compression through the depth if each higher layer is slightly thinner than the previous one (since the lower layers get some of the tamping pressure from tamping the upper ones -- this matters because, although only maximum pressure reached would matter if the coffee reached a static equilibrium after each tamp, this doesn't happen in practice as the irregularly shaped grounds will change orientation and still move a bit in a lower pressure tamp after a higher pressure one).  Instead of decreasing layer thickness, you can slightly increase tamping pressure for upper layers, or do both

Posted October 18, 2006 link

I've often thought about this method as a solution to the "lower portions not compacted" theory (which is turning out to be reality, if other applications of packing methods, eg explosives) are the forerunners.

But it raises other points too, some that, when I thought about this years ago, turned me off the idea of tamping in layers.

It goes back to an article written on CG some time ago by Fookoo - the triple basket and its packing method. He described doing it in layers to properly distribute and get the coffee in. But when I tried it myself, I found I had to ground much, much coarser than a "put it all in, distribute, level, tamp" method. I started thinking through the process, and what I came up with was this:

Say you do three dose / tamps inside a basket. dose in your first 6 grams. tamp it, even with light pressure (maybe 10lbs pressing down). Then the second with 6 grams, repeat, but harder press. Then thel ast 6 or 7 grams, 30lb tamp, polish.

In my mind's eye, I've created these three "walls" of resistance to the pressurized water - a layer of coffee that is compacted at high points three layers down, with a progressive lower density of packing within that 6 grams stage.

So the water falls down onto the top of the pack... plows through, loses kinetic energy along the way... then hits the second wall - and has to plow through that... losing more energy along the way... then makes it through, then bam, hits the third wall, and possibly by this time is spent.

So one would have to grind coarser. But in grinding coarser, we're losing something else. We're losing the volume of exposed cellular "walls" for the water to extract from - for oils and lipids to be cooerced to come along for the ride. Grinding coarser is not a solution in espresso - it's a limiter, when we're solely looking at flavour extraction capability in that 25 second brewing time. Also, if you read James Hoffmann's excellent "Crema" article, we're losing other things by grinding coarser.

Then there was another problem - at least one I thought could be a problem years ago when I was thinking about multiple-tamping levels... doing this presents more of a danger of not doing an even pack - even resistance around the entire diameter of the pack. It also presents more chance of "breaking the seal" between the side walls of the filter basket and the pack. Probably not - but my theory is - the more handling you do, the more chance you have to muck it up.

That said, I want to re-engage the multiple tamping idea - I just got a lot of fresh coffee this week again, and am flush for doing some serious experimenting - I'll give it a try again, and follow your suggestions - increasing layer thickness with each "level" you dose in the basket, and increasing the tamp pressure, or a combination of the two, and see how it works out.

Mark

 
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cv
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Posted Wed Oct 18, 2006, 5:59pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

So we got a phycisist here, but the solution comes from something chemists are more familiar with:

Well, truth told, not a practising physicist at present unless you count a thorough understanding and daily application of optics; the Newtonian physics was a long time ago. But the enquiring mind and the ability to read is still there, and enhanced with the right amount of caffeine.

It makes sense as Mark says in the next note that multiple tamps might create layers of varying resistance and that this might actually impede the smooth and consistent flow of water that we're all aspiring to. An experiment in the making though. In recent reading I've come across the suggestion (credit should go to the appropriate author) that (and in my limited experience) a bit of jiggling and gentle knocking as coffee is loaded into the filter seems to provide a more even distribution prior to applying the tamp and makes it easier to overfill if desired.

A comment (thought) on the question of why doesn't all this equalize when the grains swell. Water passing through the puck must cause some swelling but at the same time a portion of the grain is dissolved. Both of these things will change (metamorph) the shape of the coffee grains and affect 'settling' and it must be pretty complicated to predict the result. I use the term metamorph because that is the term used in evaluting the snowpack for avalanche forecasting. Moisture, vapour and liquid travel throught the snowpack as snow settles, changing the shape of the snow crystals, creating  and breaking down layers and eventually firming and evening up the snow pack. Something similar probably happens in coffee although at much higher, more even temperatures, and in a much shorter period of time. Packing explosives would give insight into the tamping stage. But a microscopic analysis (like avalanche forecasters do) of the before and after shapes of the grounds and the density throughout the puck might answer some questions. Although watching and tasting sounds like a lot more fun!
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Posted Wed Oct 18, 2006, 9:19pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

conerad Said:

how about distribution while the pf was resting on a vibrating surface? i can't thing of what you'd use offhand, but someone's gotta have some kitchen appliance in a cafe setting that rattles/vibrates like crazy.

Posted October 16, 2006 link

Actually, something similar has been tried in the past - check out some of the posts on this thread.

Inspired by Jack's experiments with a scribing pen, I tried a vibrator (don't ask :-) to see if it helped with distribution of grounds in the filter basket. It didn't, but that's not the same as a vibrating surface. I think the idea has merit.
________
John
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