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LifesAGrind
27th November 2013, 17:26
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Here's a good guide on how to address the use of new burr blades for your coffee bean grinder, and how to season those burrs for use...it's a shame most grinder manufacturers STILL don't season burrs prior to sale!

Stage one: As machined
The burr's edges are sharp, the surfaces are relatively rough from the machining tool and there may be some metal flashing and burrs on the edges. Deburring may or may not specified as part of the machining process.

Stage two: As delivered
Because, between the machining station and your home (installed in a grinder or as spare parts), the burrs will be manipulated, moved, piled and thrown around, there might be some indents and local deformations on the edges or flat surfaces. The amount of surface "damage" will depend on how careful the manufacturer's employees are with the parts.

Stage three: As installed, first run
When installed in the grinder, and first put in contact with coffee beans, the first thing that will happen is that the larger thin metal flashing will be worn away. Since they are just hanging on a thin section they are easily bend around and broken away from the burrs by the beans.

Thus "large" flashing on the burrs are not really of any concern since they will be broken away naturally and quickly upon the first few usages.

Stage four: Surface blending (peening)
The beans are much softer than the burr material. It is intuitive to think that the softer material (the beans)will be the only one that is damaged when crushed against two pieces of steel but in fact all contact surfaces are deformed, elastically, somewhat proportionally to the hardness of the steel and the beans. Obviously the bean suffer catastrophic failure and sometime the burrs will suffer some microscopic permanent local deformation.

Stretching it a bit, in engineering term this local deformation of steel surfaces by smashing it with coffee beans would be called "bean shot peening".

This peening will blend down most of the machining roughness and small machining burrs. The grinding burr edges will be slightly rounded out throughout. As well this peening may have a strengthening effect (cold hardening) on the metallic structure that may reduce the wear of the grinding burrs for the long term.

Stage five: Stabilisation
When the edges and surface roughness of the grinding burrs are all rounded down and the surfaces have been cold hardened (if it does occur), the whole mechanism should become stabilised and there should not be any significant rapid modification in the grinding burr characteristics.

Stage six: Wear
Obviously after stabilisation constant usage will create wear of the burrs. This occurs when the contact stress on the grinding burrs becomes large enough for microscopic pieces of the metal to be "chipped" away or by additional surface deformation to occur that will round out the edges even more. Both these conditions may occur when a extraordinarily hard bean is ground or a piece of foreign material such as rock or metal dust is put between the burrs. Compared to stages four and five, this stage is a very slow process.

Of course, if a "big" foreign object is put between the burrs, such as a pebble, the damage will be large and quick! You'll likely hear it if it happens.

Well then, there you have it. From my point of view and limited knowledge; Seasoning of the burrs is what happens between stage three and stage five.

Credit: Whale

It also has to be said that new burrs will take around 5 and 25 kilos of coffee to 'wear in', and normally steel burrs will last over 1000 kilos!