[Homeroast] Poisson's ratio WAS: Re: Compak vs Macap vs Rocky Grinders

David Liguori liguorid at albany.edu
Wed May 19 11:46:17 CDT 2010


No reason you couldn't define a Poisson's ratio for tamped coffee, just 
as you could define a Young's modulus (or a dynamic resistance for a 
non-ohmic electrical conductor).  They just wouldn't be simple numbers.

On 5/17/2010 2:34 PM, Mike Koenig wrote:
> Ray,
>
> Please try not to abuse scientific phenomena.  Poisson's ratio has nothing
> to do with systems of particles, and applies only to solid objects, (like
> rubber or metal).
>
> Tamping in one axis cannot correct for clumps - you will get less dense
> areas in your puck.  Applying some lateral force (I think you say you let
> the vibration of your grinder settle the puck) could take care of some
> clumping (though I'm quite curious why your grinder vibrates that much,
> doesn't seem right to me)...
>
> --mike
>
>
> On Sat, May 15, 2010 at 2:55 AM,<raymanowen at gmail.com>  wrote:
>
>    
>> The Major (Silver Fireplug; BUFF) burrs do wonderful things to coffee beans
>> once again after 5 years' use, renewed a couple of months ago.  When I
>> first
>> got it, the maintenance tag said they'd been in use for 10 years- I presume
>> at *$. There's a story in there somewhere.
>>
>> (Can they even access the burrs in their present push-button pop machines-
>> and would they?) Employees in the SCAA, SCAB or SCAM union punch in, push
>> buttons, make change, punch out and cash their check. Seems like little
>> else
>> was interesting to the majority in Denver town when I was seeking a reason
>> to enjoy espresso.
>>
>> Why seek to enjoy espresso? As I said before, I was associated with a
>> fellow
>> that won the bid on an equipment lot from the SS United States in dry
>> dock...
>>
>> "Hey, Ray- What do you know about this espresso machine?
>>
>> "Nuthin-' but I can count- it has 5 or 6 stations, and looks like it came
>> from a Tijuana Cat House, with all the black and red Naugahyde and gold
>> (polished Brass?) pieces...  Thus started my quest to find out how Real
>> Espresso should taste.
>>
>> Looks like SCAA might as well be SCCA, as much as they do for the
>> commercial
>> cup.  Almost made "Commercial" a four-letter word, instead of "Artisan" the
>> bean deserves.
>>
>> In my opinion, the Grinder is Everything.  Any real coffee shop ought to
>> keep a stack of new burrs like the Cincinnati Kid had a stack of chips at
>> the table in Las Vegas.
>>
>> Who promotes the palaver about coffee clumps surviving the packing tamp?
>> Stand up and be counted. So coffee clumps have more structural integrity
>> than the buildings in San Francisco in 1906, Philippines 1968, or Haiti
>> more
>> recently. By comparison, the raw coffee clumps out of the new burrs in the
>> Mazzer are demolished by the Richter 10.0 vibration and tamping force that
>> resolves to a tri-axial force by Poisson's ratio.
>>
>> The compression due to the axial tamping force causes transverse forces
>> that
>> tend to seal the puck in the filter basket. Otherwise, the brewing water
>> would flow around the puck instead of through it, at reduced pressure and
>> extraction and little crema formation.
>>
>> Conversely, a wine bottle cork screw can extract the cork when it's screwed
>> in less than half-way. Poisson again. Screw a wood screw into the cork, and
>> you're never pulling it out intact. P.
>>
>> So the grinder makes clumps. They can't survive packing and tamping- I have
>> some extra sharp Cheddar and Irish Dubliner that might go well with your
>> spur gear sound.
>>
>> Cheers, Mabuhay, Iechyd da -RayO, aka Opa!
>>
>> Got Grinder?
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>>      
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