I am initiating this topic in parallel to Jammin's topic not to detract from is idea and the discussion that may result.

After reading this thread, New grinder with poorly machined burrs, I started asking myself what is considered burr seasoning in this community? In the aforementioned thread it is implied that the flashing on the burrs would not be a "normal" occurrence, thus since burr seasoning would not be about wearing out these burrs what is it?

Let me explain what is my understanding of what occurs when new burrs are first used.

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.

From now on I invite the members to correct me (as required) and help define what really happens.

I think stage 5 nails seasoning on the head.

i like to think of it as polishing combined with the hardening you describe, with ultimate result being stabilization.

Sounds about right to me Sylvain, but you know much more about all this than me.

The only thing I would add is that I believe - in common with many Italians - that the coating of the burrs (especially metal burrs) with coffee oils also influences the taste profile, especially the slight metallic edge once can sometimes find when new. They believe the same about Moka pots and many won't wash them with soap for this reason, or use stainless steel which retains less oils on its surface.

Cheers

Mike

michaelbenis wrote:The only thing I would add is that I believe - in common with many Italians - that the coating of the burrs (especially metal burrs) with coffee oils also influences the taste profile, especially the slight metallic edge once can sometimes find when new. They believe the same about Moka pots and many won't wash them with soap for this reason, or use stainless steel which retains less oils on its surface.

You will not get any argument from me there. I would assume that the coffee oil coating would occur after very few usage.

I have written numerously that I hate the taste of soap but I also hate the taste of metal. As much as I can I do not drink beer that comes in a can because of the metallic taste that it has even is the aluminum is coated with a film of polymer (I have to make an exception for Guinness and Kilkenny which I can only get in cans...).

Sylvain,

Although I am on the same page w/you about the oil coating happening quickly but do you think it may be possible that the oil might not be able to form a solid coating until the burrs are stabilized?

I did note that while my new burr-set was breaking in, i found a dinstinct metallic taste. I was also working with a brand new machine so I could not say specifically if the burrs were the culprit.

I agree w/you though on metallic tastes and find them very unpleasant as well.

Totally off-topic, but they do make bottled Guinness. It's very nice on its own, but also goes quite nicely with a double vodka....

Don't ask em how I know

^absolutely. It comes with the "rocket widget" inside the bottle. Thats with the draught anyway. The stout is just bottled regularly. I prefer the drought though.

Maybe we should start another thread... but I find that it goes very well with a 12 year old Macallan or a 16 year Bushmill, both have a honey taste that balances the plumpness of the Guiness. Actually, I'm gonna have me one of those combo tonight!

Back to the topic...

jammin wrote:Although I am on the same page w/you about the oil coating happening quickly but do you think it may be possible that the oil might not be able to form a solid coating until the burrs are stabilized?

If what I wrote at the beginning hold any water, than the seasoning should "smooth out" the surfaces and reduce the areas for the oil to accumulate and thus reduce the amount of oil retained.

Actually this would be a benefit in my view. Coating might be a good thing to prevent metallic taste but too much retention of oil could be a bad thing for both taste transfer between shots (which is a phenomenon still under discussion) and racid oil which I believe everybody agrees on.

Here is a post about seasoning. Interesting. Now pass me the Guinness and scotch. http://www.jimseven.com/2011/06/15/dear-grinder-manufacturers/