Coffee Grinder Burrs Have Geometry?

Coffee grinders use burrs, as you know. But what separates burr grinders from other methods used for grinding coffee?

The difference is that pulverising beans with something heavy, causes beans to explode into non-uniform shapes and sizes, similar is also true of blades, while
burrs break beans into more uniform chunks, by chewing them (for the want of a more appropriate verb).

It doesn't matter so much if you're wanting to turn something into a very fine powder, such as when milling flour, because the particle uniformity at that point becomes much more even.

Coffee beans were initially ground by crushing them with boulders, or by crushing them in early mortar and pestles.

Early coffee grinders, thought to have been a Turkish invention, worked like very small grinding mills, mini versions of a mill with a millstone for creating flour for example.

A dentist by the name of Thomas Bruff (Thomas Jefferson’s dentist, believe it or not!) was the first to come up with the idea (or at least the first to achieve a US patent for it) of using two sets of specifically designed teeth, to basically chew beans in a similar way that upper and lower sets of teeth chew.

This worked so well that burrs became the norm for coffee grinding. Burr grinders these days all have a set of upper and lower, or inner and outer (when talking about conical burrs as opposed to flat) burrs, with "teeth", which work together to cut beans into uniform chunks.

This is except for the very cheapest "burr grinders" (Krups expert, DeLonghi KG79, Melitta Molino) which have blunt "grinding disks", on which the only sharp part is actually the tops of the screws holding the disks in place, which explains their poor performance where grind uniformity is concerned.

 

The Best Electric Coffee Grinders

So, what is Burr Geometry?

I'm explaining this because I mentioned burr geometry in a conversation recently, and was met with a puzzled expression ;-), I then realized that this is a needlessly complex sounding term to describe something that is ridiculously simple.

 

Not that I'm going to stop dropping terms like that into conversation of course, makes me sound clever, despite being as thick as pig muck ;-).

All "burr geometry" means, is teeth pattern, or cutting pattern, that's it, nothing complex at all.

It's become apparent over the years that the teeth pattern - burr geometry - is what makes the most difference to grinders. This is why many people will upgrade their grinders these days by simply swapping out the burrs.

This is also what makes some grinders better for certain brew methods than others, because certain burr geometries lend themselves to better particle uniformity and greater traction (and therefore faster grinding speed) within particular particle size ranges, meaning that some burr sets are better for espresso, some are better for coarser ranges such as filter & cafetiere.

For example, the Baratza Forte comes with two sets of high quality Ditting burrs, a ceramic burr set with a geometry focussed on espresso, and a steel burrset which has a better geometry for pour over and other manual brew methods requiring a larger grind size.

So there you go, the next time see anything relating to "burr geometry", there's no need for your eyes to glaze, although it sounds very nerdy, it just means the shape and position of the cutting pattern (teeth) on the upper and lower or inner and outer burrs.