Our Valued Sponsor
OpinionsConsumer ReviewsGuides and How TosCoffeeGeek ReviewsResourcesForums
Articles: CoffeeGeek Columnist Feedback
Tamping Science, Theory and Practice, Part One by Mark Prince
Cafe Espresso Machines
Video reviews, nationwide installation, leasing options... Nuova Simonelli, Rancilio, La Marzocco.
www.seattlecoffeegear.com
 
Not Logged in: Log In to Postlog in
New Topics updated topics   New Posts new posts   Unanswered Posts new unanswered  
Search Discussion Board search   Discussion Board FAQ faq   Signup sign up  
Discussions > Articles > Columnist... > Tamping Science,...  
view previous topic | view next topic | view all topics
showing page 8 of 10 first page | last page previous page | next page
Author Messages
scottfranklin
Senior Member


Joined: 27 Nov 2006
Posts: 39
Location: Rochester
Expertise: I love coffee

Espresso: Alex Duetto II, Faema...
Grinder: Baratza Vario
Posted Mon Nov 27, 2006, 11:12am
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

As another newbie, let me add my thanks to Mark for a fascinating article.  Tamping/distribution seems so subjective, it's great to see it tackled systematically (that's why it's coffeeGEEK i guess).  I didn't think I'd be able to contribute anything of substance this early (repeat:  NEWBIE, be nice!), but here goes.

Regarding force on the sidewalls, AndyS wrote:

First of all, the outward force on coffee particles at the edge of the basket is very small. Outward force is related to downward force via a sine function, and the sine of the shallow angles we have on convex tampers is very small. In other words, the outward force on a coffee particle near the edge is miniscule.

This would be true if the coffee were continuous  Because it's actually lots of smaller particles, however, things change.  Granular materials not only laterally deflect vertical forces (see force chains, http://jfi.uchicago.edu/granular/force_chains.html), they amplify them as well.  This is one reason grain silos typically explode outward along the walls rather than collapsing under the weight; a ton of grain can exert considerably larger forces along the walls.  This also explains why tamping doesn't produce much compaction at the bottom.  The large forces on the side result in large upward frictional forces that balance the tamping force.  The result is that the coffee at the bottom doesn't know you're tamping at the top (the Janssen effect, http://denali.phys.uniroma1.it/~puglisi/thesis/node5.html).

I'm very curious to read about the results of vibration before tamping.  Vibration should uniformly increase compaction, but I think Mark found (see his post on bouncing) why it often fails in practice:  the slightest asymmetry in the process causes grains to heap or otherwise become less uniform.  And any subsequent disturbances probably ruin the careful work of bouncing, leveling, tamping, etc...

Thanks again for this awesome thread.  I've gotten so many ideas to try; I can't wait to kick my family out of the house for the day so I can grind, tamp, (no knocking!), pull, drink, and repeat until I collapse a jittery heap on the floor.

Scott
back to top
 View Profile Visit website Link to this post
andys
Senior Member
andys
Joined: 10 May 2003
Posts: 861
Location: NY
Expertise: Just starting

Espresso: Speedster, Londinium 1
Grinder: EK-43,Robur, HG One, M3
Vac Pot: Yama
Drip: various
Roaster: PIDed Popper
Posted Mon Nov 27, 2006, 7:22pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

scottfranklin Said:

Regarding force on the sidewalls, AndyS wrote:

This would be true if the coffee were continuous  Because it's actually lots of smaller particles, however, things change.  Granular materials not only laterally deflect vertical forces (see force chains, http://jfi.uchicago.edu/granular/force_chains.html), they amplify them as well.  This is one reason grain silos typically explode outward along the walls rather than collapsing under the weight; a ton of grain can exert considerably larger forces along the walls.  This also explains why tamping doesn't produce much compaction at the bottom.  The large forces on the side result in large upward frictional forces that balance the tamping force.  The result is that the coffee at the bottom doesn't know you're tamping at the top (the Janssen effect, http://denali.phys.uniroma1.it/~puglisi/thesis/node5.html).

Posted November 27, 2006 link

Hi Scott, you're a friend of Wes, right? I hope you guys can come over for espresso sometime soon.

Thanks for the kickass post, it is fascinating. You made one mistake, though: typically, grain silos DON'T explode!

Hahaha.

Do you know the difference in behavior between "granular materials" and coffee ground to espresso fineness? (I don't). Finely ground coffee is oily and sticky and may behave a little differently than the glass spheres studied in the first article above.

scottfranklin Said:

I'm very curious to read about the results of vibration before tamping.  Vibration should uniformly increase compaction, but I think Mark found (see his post on bouncing) why it often fails in practice:  the slightest asymmetry in the process causes grains to heap or otherwise become less uniform.  And any subsequent disturbances probably ruin the careful work of bouncing, leveling, tamping, etc...

Posted November 27, 2006 link

Have you tried it? I tried vibrating some portafilters with an upside down electric sander, but the results so far were unimpressive.

scottfranklin Said:

I can't wait to kick my family out of the house for the day so I can grind, tamp, (no knocking!), pull, drink, and repeat until I collapse a jittery heap on the floor.

Posted November 27, 2006 link

Been there, done that.  :-)

 
-AndyS
picture page:  http://flickr.com/photos/andy_s/sets/
back to top
 View Profile Visit website Link to this post
scottfranklin
Senior Member


Joined: 27 Nov 2006
Posts: 39
Location: Rochester
Expertise: I love coffee

Espresso: Alex Duetto II, Faema...
Grinder: Baratza Vario
Posted Tue Nov 28, 2006, 6:10am
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

]Hi Andy (and others),

Do you know the difference in behavior between "granular materials" and coffee ground to espresso fineness?

I was afraid someone would notice this; thanks for calling me on it.  There's two points, and you nail them both.  First, espresso grounds are finer; Click Here (temesblog.blogspot.com) tests a number of grinders and puts the particles anywhere from 1 to 500 microns.  At the larger size I believe they act more granular (force chains, etc).  I'm still looking to see what happens in powders.  My instinct says there should be some inhomogeneity of forces (after all, if there are spaces, it can't be uniform), but I don't know.  Also, no clue how things change as the coffee gets compacted into the puck.  

The second point is the oilyness and, again, the research is lacking.  (The joke among physicists is to start by assuming all cows are spheres, so assuming all spheres are hard & non-sticky is the next step I guess).  

I tried vibrating some portafilters with an upside electric sander, but the results so far were unimpressive.

This would be horizontal vibrations, right?  My thought was to go with small vertical oscillations, maybe (WARNING:  stream-of-conciousness thought to follow, grain of salt included) resting the portafilter on top of a speaker (aimed upwards) and blasting some Metallica or old REM.  (Mark:  need a new article on compaction of different musical genres!).  Powders compact like granular materials do (see Fig. 2 in www.grasp.ulg.ac.be/research/papers/2006_lumay_APL.pdf); 20 taps (~5 seconds of End of the World) gets you halfway to maximum (unpressed) compaction.

Hi Scott, you're a friend of Wes, right? I hope you guys can come over for espresso sometime soon.

I don't think I know Wes, but I never turn down espresso.

Scott
back to top
 View Profile Visit website Link to this post
Prune
Senior Member


Joined: 15 Sep 2002
Posts: 29
Location: Vancouver
Expertise: I love coffee

Espresso: Heavily modified old machine
Grinder: Solis Maestro
Roaster: iRoast2
Posted Tue Dec 5, 2006, 1:23am
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

MarkPrince Said:

.... aka, the portafilter "bounce".... covered in depth in Article 2, which should be online right after we get a new columnist (another one besides Jim) up and running.

Mark

Posted October 18, 2006 link

You misattributed the quote.  I didn't write that, cv did.
back to top
 View Profile Link to this post
Prune
Senior Member


Joined: 15 Sep 2002
Posts: 29
Location: Vancouver
Expertise: I love coffee

Espresso: Heavily modified old machine
Grinder: Solis Maestro
Roaster: iRoast2
Posted Tue Dec 5, 2006, 1:36am
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

scottfranklin Said:

The second point is the oilyness and, again, the research is lacking.  (The joke among physicists is to start by assuming all cows are spheres, so assuming all spheres are hard & non-sticky is the next step I guess).

Posted November 28, 2006 link

The solution is quite simple: computer simulation.  If I weren't so busy, I'd code one myself...

On another note, did anyone do vibration during tamping?
back to top
 View Profile Link to this post
welone
Senior Member


Joined: 18 Dec 2006
Posts: 42
Location: Baden, Switzerland
Expertise: I love coffee

Espresso: paddle GS3,...
Grinder: Compak K10, Baratza Vario,...
Posted Mon Dec 18, 2006, 4:31pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

Hello from little Switzerland

Tamping in two layers resulted repeatedly in my puck breaking horizontaly apart (between the two tamping layers) when I discarded it. This could indicate for an effect you described as walls between the layers which could disturb the waterflow

MarkPrince Said:

...In my mind's eye, I've created these three "walls" of resistance to the pressurized water...
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.

Posted October 18, 2006 link

Thanks a lot for all this useful articles!

Marco
back to top
 View Profile Link to this post
slidingmike
Senior Member


Joined: 10 Jul 2005
Posts: 84
Location: San Francisco
Expertise: I love coffee

Espresso: Anita
Grinder: Mazzer Mini
Posted Thu Jan 18, 2007, 1:56pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

Just a bump to see if we can prod for the release of part II...  This is fascinating stuff.

As an aside, when I first heard someone apply "Euro Curve" to a tamper, I laughed.  Growing up playing hockey in Canada, that's what we called the over-curved sticks used by European hockey players.  Good for wrist shots, not so good for backhand shots...  I wonder if Reg, if he coined the term for tampers, had that on his mind.

Cheers,
Mike
back to top
 View Profile Link to this post
ProLost
Senior Member


Joined: 31 Dec 2006
Posts: 14
Location: San Francisco
Expertise: I love coffee

Espresso: Expobar Brewtus II
Grinder: Mazzer Mini, KA Pro Line
Drip: Milita pourover
Posted Sun Feb 4, 2007, 1:58pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

andys Said:

...First of all, the outward force on coffee particles at the edge of the basket is very small. Outward force is related to downward force via a sine function, and the sine of the shallow angles we have on convex tampers is very small. In other words, the outward force on a coffee particle near the edge is miniscule.

But more importantly, if you're concerned about thorough compaction along the edge of your coffee cake, the convex tamper is the last thing you'd want. The convex tamper applies LESS force at the edge, because it contacts the center first. The center gives only so far before it has compacted as far as it can with the amount of force you're applying. Then it resists, preventing further downward movement. The result is a pattern where the degree of compaction is greatest in the center and least at the edge, which presumably is just what you DON'T want...

Posted November 12, 2006 link

This sounds correct to meI wonder if anyone would care to try to rebut this argument?

And let me add to the voices begging for parts two and three. Mark, as a fellow perfectionist/procrastinator, I beseech you to let go and post part two even if that movie isn't shot yet!

-Stu
back to top
 View Profile Visit website Link to this post
Philosopher
Senior Member


Joined: 13 Feb 2007
Posts: 188
Location: Australia
Expertise: I like coffee

Espresso: Silvia
Grinder: Rocky
Posted Tue Feb 13, 2007, 7:19am
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

I thought Hug made a important observation about tamping and compaction.  Perhaps we need to apply a bit more scientific theory to all of this rather than just speculating on the right answers?

It is assumed that through careful attention that most Baristas are able to control such variables that lead to an even, consistent and optimal extraction.

However, Mark's observations about tamping pressure show that even controlling one variable such as consistency in compaction throughout the dose is not as easy as it seems.  

When laying a strong foundation for paving or road work, it is a fundamental principle that you should not lay more than a few inches of rubble down before beginning compaction.  This is aided by vibration which allows the irregular fragments to jostle tighly against each other and form a compact tesselation of particles.  Ignoring this principle results in a loose network leads to subsidence and sinkage - much like a mushy puck.

Simple physics would suggest that other variables will also vary signicantly within the basket.  Even in a perfectly tamped dose, various natural gradients form as you move down through the basket including:

Temperature
Pressure
Solute concentration

So near the end of the pour as the bottom grounds begin releasing their flavour, it is possible that the top grounds are already becoming overextracted.

In an optimal configuration each individual ground should be exposed to the same conditions as its neighbours.  In practice clearly this is much harder to achieve.

Perhaps there is someone out there with more of an engineeering background who might be able to model this better and suggest the best solution to achieve the optimal result.
back to top
 View Profile Link to this post
Philosopher
Senior Member


Joined: 13 Feb 2007
Posts: 188
Location: Australia
Expertise: I like coffee

Espresso: Silvia
Grinder: Rocky
Posted Tue Feb 13, 2007, 6:10pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

A couple things about of all of this:

Vibration
 I note that some of us have tried this idea (including one person who used an electric sander).  I suspect that vibration can work for or against you.  If the magnitude of the vibration is too large then it will only serve to loosen the particles and aerate them.  I suspect that the fineness of the coffee grounds require much lower amplitudes then can be provided by most standard electrical tools.  Vibration and presssure also need to occur simultaneously to prevent the particles dislodging from one another during the process.  At the end of the day it would be hard to conceive an automated gadget which could incrementally fill, compact, vibrate something as small as a basket.

Grind consistency
 As noted somewhere else I read, it would seem more logical to have coffee particles of differering sizes to minimise gaps in the puck e.g. smaller ones to fill the gaps between the larger ones.  Why then this obsession with burr grinders and consistency in grind?  Perhaps you need a more bimodal distribution of grind sizes to achieve optimal compaction. e.g. a bit of gravel and a bit of sand.

Tobacco analogy
 This is an interesting point because it does recognise that the physical characterstics of the puck changes dynamically during the pour.  The higher pressure gradients near the bottom (subject to gravity of the particles above) are enhanced by the swelling of the coffee particles.  I note that someone mentioned that pressure is equal in a sealed chamber.  This is true if there is no flow - all pressures will equilibrate.  However, during a flow state then there is a natural pressure gradient formed.  Flow always occurs from an area of high pressure to low pressure.
back to top
 View Profile Link to this post
showing page 8 of 10 first page | last page previous page | next page
view previous topic | view next topic | view all topics
Discussions > Articles > Columnist... > Tamping Science,...  
New Topics updated topics   New Posts new posts   Unanswered Posts new unanswered     Search Discussion Board search   Discussion Board FAQ faq   Signup sign up  
Not Logged in: Log In to Postlog in
Discussions Quick Jump:
Symbols: New Posts= New Posts since your last visit      No New Posts= No New Posts since last visit     Go to most recent post= Newest post
Forum Rules:
No profanity, illegal acts or personal attacks will be tolerated in these discussion boards.
No commercial posting of any nature will be tolerated; only private sales by private individuals, in the "Buy and Sell" forum.
No SEO style postings will be tolerated. SEO related posts will result in immediate ban from CoffeeGeek.
No cross posting allowed - do not post your topic to more than one forum, nor repost a topic to the same forum.
Who Can Read The Forum? Anyone can read posts in these discussion boards.
Who Can Post New Topics? Any registered CoffeeGeek member can post new topics.
Who Can Post Replies? Any registered CoffeeGeek member can post replies.
Can Photos be posted? Anyone can post photos in their new topics or replies.
Who can change or delete posts? Any CoffeeGeek member can edit their own posts. Only moderators can delete posts.
Probationary Period: If you are a new signup for CoffeeGeek, you cannot promote, endorse, criticise or otherwise post an unsolicited endorsement for any company, product or service in your first five postings.
Great Espresso at Home
Curated selection of the best machines from La Spaziale, Izzo, Quick Mill, La Marzocco & more.
www.clivecoffee.com
Home | Opinions | Consumer Reviews | Guides & How Tos | CoffeeGeek Reviews | Resources | Forums | Contact Us
CoffeeGeek.com, CoffeeGeek, and Coffee Geek, along with all associated content & images are copyright ©2000-2014 by Mark Prince, all rights reserved, unless otherwise indicated. Content, code, and images may not be reused without permission. Usage of this website signifies agreement with our Terms and Conditions. (0.330348968506)
Privacy Policy | Copyright Info | Terms and Conditions | CoffeeGeek Advertisers | RSS | Find us on Google+