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Tamping Science, Theory and Practice, Part One by Mark Prince
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Prune
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Posted Tue Feb 13, 2007, 7:33pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

Philosopher Said:

suggest the best solution to achieve the optimal result.

Posted February 13, 2007 link

The goal here is to even out the extraction from each particle.

One approach would be solvent extraction in a Gregar extractor, with precisely controlled temperature profile and varying mix of different solvents to optimize extraction of the preferred substances.  The result can be vacuum packed and frozen.  Perfect espresso from the microwave (of course, no crema, but the usual crema contents will be there). :)

In the context of an espresso machine, a completely different group-head design with a very wide and very shallow basked could be used, such that all the coffee is virtually simultaneously extracted as the travel time through the basked will be insignificant.
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Philosopher
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Posted Tue Feb 13, 2007, 8:25pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

Prune Said:

The goal here is to even out the extraction from each particle.

One approach would be solvent extraction in a Gregar extractor, with precisely controlled temperature profile and varying mix of different solvents to optimize extraction of the preferred substances.  The result can be vacuum packed and frozen.  Perfect espresso from the microwave (of course, no crema, but the usual crema contents will be there). :)

Posted February 13, 2007 link

I am not familiar with the process but I presume the solvents can be removed and are non-toxic.  I gather that the aesthetics of crema (if not the flavour) are produced by tasteless carbon dioxide.

A technically correct answer if not romantically appealing but I guess we could easily engineer another step that will make the result acceptable to the discerning
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Philosopher
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Posted Tue Feb 13, 2007, 8:33pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

Prune Said:

The goal here is to even out the extraction from each particle.

In the context of an espresso machine, a completely different group-head design with a very wide and very shallow basked could be used, such that all the coffee is virtually simultaneously extracted as the travel time through the basked will be insignificant.

Posted February 13, 2007 link

This was what I was thinking but there is another variable that we have not considered.  Perhaps there is an optimal dwell time to achieve adequate diffusion of the components out of each coffee ground.  If the flow of water is too rapid then there is no time for the flavours to be released.  

Ideally all particles are exposed to the same conditions (temperature and pressure) in a sealed chamber before the liquid is suddenly released.

Maybe there is some merit in the presssurised portafilter - but one with a timed pop-off valve.
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Philosopher
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Posted Tue Feb 13, 2007, 8:49pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

Philosopher Said:

This was what I was thinking but there is another variable that we have not considered.  Perhaps there is an optimal dwell time to achieve adequate diffusion of the components out of each coffee ground.  If the flow of water is too rapid then there is no time for the flavours to be released.  

Ideally all particles are exposed to the same conditions (temperature and pressure) in a sealed chamber before the liquid is suddenly released.

Maybe there is some merit in the presssurised portafilter - but one with a timed pop-off valve.

Posted February 13, 2007 link

Come to think about it - perhaps we should refine piston espresso machines to be more like a car engine i.e.

Heated water and grounds are introduced into a via an intake valve into a cylinder, agitated to optimise even exposure of the particles, pressurized and then suddently released through a pressurised exhaust valve.

To achieve optimal extraction you could still control the following variables:

Fineness of ground
Temperature of water
Dwell time
Pop-off pressure

However the problem of evenness in extraction/inconstant compaction is removed.
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iZappa
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Posted Wed Feb 14, 2007, 2:16am
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

Prune Said:

In the context of an espresso machine, a completely different group-head design with a very wide and very shallow basked could be used, such that all the coffee is virtually simultaneously extracted as the travel time through the basked will be insignificant.

Posted February 13, 2007 link

But you are forgeting here that various flavours in the coffee extracts at different time. And that by reducing the shot time, or keeping the shot time the same but grind finer, you will get a different result in the cup.

Read Jim Schulman's excellent article on over- and underdosing your pf for varius degrees of sour/floral and bittersweet tastes.

Some Aspects of Expresso Extraction
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Prune
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Posted Wed Feb 14, 2007, 2:20am
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

iZappa Said:

But you are forgeting here

Posted February 14, 2007 link

I'm forgetting nothing, but you seem to have a problem with reading comprehension.  I am clearly not implying that the time of extraction is shortened, but that a given 2D slice of the water column downwards through the grouphead passes through all grounds in a very short amount of time, thus preventing the development of a significant solute concentration differential between the top and bottom of the grounds.  The overall extraction time (= grounds immersion time) can easily remain the same.

Alternatively, what Philosopher suggested is workable: piston driven machine with three phases, t0 is initial mixing time, t1 is immersion time, and t3 is filtration time.  The optimal setup would have t0, t2 << t1, which is possible if a very powerful piston mechanism and strong filter are used.  Note that t1 can easily be pressurized to mimic the conditions in a regular grouphead, but now you have separate control over extraction pressure and filtration pressure.

BTW, drop by #diyaudio on irc.rizon.net if you want to chat about this, and I'll try to explain it better.
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ThatCoffeeGuy
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Posted Thu Feb 15, 2007, 9:45am
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

I love where this thread is going!  We are now even diving into different extraction sciences, theories, and practices.  How cool!  Some of it flies over my head, but then I sort of research around and find out more about it.  There is some definite merit to these different ideas about extraction, group size/shape, etc.

Mark... really man, I'm dying here... 2 and 3?  Please?  Can I have the prototype? haha.

-Bry

 
Bryan Wray

"I just hope that people realize that coffee is not just a caffeine delivery service, it can be a culinary art." -Christopher Owens
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barngal
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Posted Sat Feb 24, 2007, 10:37am
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

oops...missed a page...
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fullbodied
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Posted Fri Mar 23, 2007, 9:47pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

Mark, I just wanted to tell you I learned a lot from this! Thanks for all the hard work you do.
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Jen_Savage
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Posted Tue May 15, 2007, 3:01pm
Subject: Re: Tamping Science, Theory and Practice, Part One by Mark Prince
 

Hey, this is the way I do it actually! I didn't know you were supposed to "knock it", so I've always done it the way Mark describes having discovered.

Neat.

Now I have to give the knocking thing a shot.
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