Given that most retail grinders are made of metal parts which should not warp too much during grinding, why would having enough bean weight impact their grind consistency? Why doesn't this happen with single dose grinders?

+1

Great question. I was told that by making changes to the grind chamber it was possible to reduce the retention. But how single grinders solve the "beans weight in the hopper" problem, I have not read about it anywhere...

Many metals are elastic. That is why they make excellent fasteners. Elastic metals can fluctuate. the bigger the burrs the more leverage the hard beans exert on the shearing surfaces.

Does it really matter? I am sure, that at least in theory, it can.

I never bought into (nor even understood) the hopper weight issue. Sounds to me like just bad design...

I seriously doubt that any metal is deforming under grinding loads. MAYBE a teeeeny bit with flat burrs.

I think the obvious reason is that with increased pressure from a mass of beans above, the beans themselves are exerting some force on each other. More pieces of beans are in the stages of the grinding burrs and smashing against each other. It's not too hard to visualize how this might have an effect of making the grind finer than with just a solitary bean chunk in there (you have to adjust the grind setting finer with less beans in the hopper). If you look at the gap of burrs, the grinds come out significantly smaller than that gap, so there must be some bean-on-bean (or grind-on-grind) action going on in there in any event - just more when there is more bean pressure. Simple?

All just speculation, of course.

I am thinking now about getting a new grinder. I kind of go back and forth between EG-1 and MK PEAK. Everybody writes that K30 (and PEAK, for that matter) is not suitable for single dosing. That it requires at least 2" height of beans in the hopper. I can accept this axiom, moreover, people complain about the grinds not being uniform, from their experience. But how EG-1 or Monolith solve this problem?

What tricks in the design of single dose grinders cope with this problem?

The hopper grinders don't need the column of beans for good grind quality. It needs it to remain consistent. The grinds you produce with no beans in the hopper will produce a different flow than if you did have a full hopper and you have to adjust the settings accordingly.
If you always keep it empty or always keep it full, you will not run into inconsistencies. (the single-dosers are effectively always empty..)

DaumierS wrote:I am thinking now about getting a new grinder. I kind of go back and forth between EG-1 and MK PEAK. Everybody writes that K30 (and PEAK, for that matter) is not suitable for single dosing. That it requires at least 2" height of beans in the hopper. I can accept this axiom, moreover, people complain about the grinds not being uniform, from their experience. But how EG-1 or Monolith solve this problem?

What tricks in the design of single dose grinders cope with this problem?

This it seems may also have something to do with retention as a result of built in "anti clumping / anti static" devices. It seems, that almost all the on demand grinders (aside from dosered versions) have them and single dose grinders do not..

So maybe the weight of a bean column helps more evenly discharge grounds as well?

May be, but I'd expect that the force applied by the burrs is so big, that the pace the beans enter the space between the burrs have little to do with the pace the grinded coffee exits that space. How built in can cause irregularity of the grinds? People write that without beans in the hopper the first and the last parts of grinds turn out to be coarser than the middle part, if I understood it correctly.

But this should be true both for commercial and single dose grinders, right? I do not understand this. Denis and Lyn and Weber do not comment about this at their web sites (though mention nearly zero retention). However, the Socrates café particle size distribution for the Monolith and EG-1 indicates the uniformity of the grinds. How?
And why this is not the case with singe dosing with the PEAK?

DaumierS wrote:May be, but I'd expect that the force applied by the burrs is so big, that the pace the beans enter the space between the burrs have little to do with the pace the grinded coffee exits that space. How built in can cause irregularity of the grinds? People write that without beans in the hopper the first and the last parts of grinds turn out to be coarser than the middle part, if I understood it correctly.

I was referring to the grinds coming out AFTER they are ground. Meaning, do we know what particles get trapped by the chute / and screen? After the coffee is past the sweepers, there is no force pushing them past the chute when single dosed.

Is it possible that having a consistent flow INTO the chute while hopper dosing helps to regulate what comes out? Beyond me.

Grind normalization might as well be a lecture in thermodynamics to me, I don't understand either!

I've seen a video at youtube showing grinding a large batch with the EG-1 and the hopper. It would be interesting if someone could repeat the experiment and comment about the taste difference between hopper grinding and single dosing with EG-1 or the Monolith. May be single dosers also benefit from using the hopper?