Pressed vs Milled Burrs

[BoldJava]

I remember asking the difference between the two burrs once before.  Snagged this post off Twitter from MPrince.  A picture is worth a 1000 words.  Both are Dittings:

http://www.flickr.com/photos/coffeegeek/3643163444/

B|Java

[peter]

Unless your grinder is used for espresso, IMHO it doesn't matter.



I think a good test for coffee-ground particle uniformity is the vac-pot.  My lowly KitchenAid Proline with the cheapo burrs never stalls.  And in my press-pot, I grind fairly fine, and it has minimal sludge.

[milowebailey]

interesting.  

What stands out to me in the photos is teeth design is very different on the two burrs


The milled one has more and longer teeth.

I think of table saw blades and what makes a good blade from a bad one.

1) The steel used
2) The design
3) The tooling used to cut the cutters

A Freud blade vs a cheap China made knock off.

I suspect the differences in those two blades are more the above three things than what form the steel was in before the machining took place.

[ktulu64]

you might not be able to as easily discern from the photos, but the pressed edges are not as sharp as those that have been milled.  Now, even the pressed burr has a section near the edge that has been milled, but the totally milled burr has sharper initial cutting edges (less bashing more slicing).  By initial, I mean the inner diameter teeth.  They both have milled outter sections because this determines the final grind particle size and that needs the precision that milling provides.  (this is primarily for espresso grind - drip grind could have more slop in it, and it would not have as large of an impact to the final product as it would with espresso) 

of course, you could run your coffee grounds through a particle separator and have perfect extraction every time (or would that be going overboard...      )

[peter]

Then there's the debate over which type of particle has better extraction, the cut/sliced particle from sharp burrs, or the jagged particles from getting crushed in less than sharp burrs.

Supposedly the jagged, crushed particles have a greater surface area than the shaved/sliced particles, and offer better extraction.