The Italian style tamp

#1: Post by **LGB** » April 12th, 2009, 5:33 pm

Seeing people use the plastic tamper thingy in front of the doser made me think: Why use so much pressure when tamping? How I picture it: The Italian style tamp (using the plastic tamper thingy or just the weight of a nice metal tamper) might make a distribution defect show up more pronounced because the uneven density doesn't get compensated by the tamping, whilst a perfect distribution will still produce the same result because the water pressure will be the same everywhere (the coffee won't be stirred up then, right?). Of course one might want to adjust the grind settings...

Comments please?

#2: Post by **malachi** » April 12th, 2009, 6:21 pm

Tamping is just a way to preserve the coffee bedding.

#3: Post by **drdna** » April 12th, 2009, 9:27 pm

I have to disagree that tamping does not aid in distribution.

In my opinion, It DOES.

Think about it. If you have a pile of sand in your sandbox and push down on top, what happens? It goes out to the sides, redistributing the grains of sand more evenly. In fact, this doesn't require a lot of pressure to accomplish.

The same with coffee grounds, to a point. At a certain point, the grounds will interlock and any added compression force will be absorbed by the mechanical torsion of the multigrain structure of the bed, much like a strain gauge, unless enough force is applied asymmetrically to the bed to disrupt the structure (which is how we get cracks and fissures).

So basically, a light tamping force helps to redistribute the grounds a bit.

A firmer tamping force makes a solid bed that might resist the water's disruptive force that can redistribute the grounds. To a point it will also compensate thusly for a coarse grind.

A very firm tamping force increases the risk of channeling.

April 13th, 2009, 4:51 am

drdna wrote:I have to disagree that tamping does not aid in distribution.

In my opinion, It DOES.

Maybe I didn't make myself clear enough (sorry 'bout my language abuse

) but that's exactly my point. In my opinion (and I think I'm not the only one) the distribution is what counts. Everything you do afterwards (redistribute, tamping hard etc) is just a fix and the aim should be to minimize these rituals...

Think about it. If you have a pile of sand in your sandbox and push down on top, what happens? It goes out to the sides, redistributing the grains of sand more evenly. In fact, this doesn't require a lot of pressure to accomplish.

The same with coffee grounds, to a point. At a certain point, the grounds will interlock and any added compression force will be absorbed by the mechanical torsion of the multigrain structure of the bed, much like a strain gauge, unless enough force is applied asymmetrically to the bed to disrupt the structure (which is how we get cracks and fissures).

Yes it is an interesting point you make (I've already read it elsewhere) and I'm pretty sure this must be what happens... Still I'd like to see a physical simulation or some other quasi-scientific research.

So basically, a light tamping force helps to redistribute the grounds a bit.

A firmer tamping force makes a solid bed that might resist the water's disruptive force that can redistribute the grounds. To a point it will also compensate thusly for a coarse grind.

A very firm tamping force increases the risk of channeling.

That would be another reason to avoid hard tamping...

#5: Post by **Bluecold** » April 13th, 2009, 6:41 am

LGB wrote: Yes it is an interesting point you make (I've already read it elsewhere) and I'm pretty sure this must be what happens... Still I'd like to see a physical simulation or some other quasi-scientific research.

I remember reading something about particle behaviour in funnels (sand), i don't know specifics, but i do remember it was very difficult. I can only imagine coffee would be much harder to model. You'd have to deal with wide particle size distribution and stickiness. Which are all variables depending on grinder, age of burrs, age of coffee, humidity, origin of coffee and roast depth. And that's without considering the irregularity of the shape of the grounds and static. So i don't think physical simulation with computers is going to happen anytime soon.

The only way i can think of to measure the redistribution by tamping would be to mix metal dust in the grounds and take an x-ray before and after tamping in a plexiglas basket. Sadly i don't have an x-ray apparatus. And i missed out on the ebay auction for some Rodenstock XR heligon lenses, so it's not going to happen anytime soon.

#6: Post by **Theodore** » April 13th, 2009, 8:46 am

...Sadly i don't have an x-ray apparatus...
Ask a dentist to help.He has.

#7: Post by **hbuchtel** » April 13th, 2009, 10:14 am

I wish folks here would write "my hypothesis is ..."

Regards, Henry

April 13th, 2009, 10:29 am

It is...

#9: Post by **drdna** » April 13th, 2009, 11:18 am

LGB wrote:Yes it is an interesting point you make (I've already read it elsewhere) and I'm pretty sure this must be what happens... Still I'd like to see a physical simulation or some other quasi-scientific research.

It is extremely well described in numerous experimental studies in the analytic and physical chemistry of laminar and nonlaminar flow of particulate solids. This is much more a concern to geologists and construction engineers than espresso makers. If you enjoy mathematics, you can find something here. Not the exact article I was looking for, but it gives you an idea of what you're in for.

One implication is that by pouring a slurry of coffee grounds and water, we can eliminate channeling. This works extremely well in the experiments I have done, but ends up acting like an extended preinfusion, so the resultant cup has a lot of drip coffee character. Oh man, that is getting off topic.

#10: Post by **Stuggi** » October 24th, 2009, 9:03 am

If look around a bit, there has to be an Italian university paper on this, they have one on everything else involving coffee.