http://blog.coffeereview.com/espresso/p...densation/

I 'm wondering if this idea will gain any traction here. It seems to me to be implausible that you would taste a difference. Have others heard of this before and, if so, do you apply the principle?

The entry is only a year old, but probably recycled; it sounds like the stuff he was writing five years ago.

Overly complicated distributing and tamping rituals are now out of fashion; they do not accomplish anything other than stopping channeling, and longer experience with bottomless PFs has made reliable dosing and distribution procedures ever simpler.

When you turn on the pump for a shot, and before the espresso comes out, the fines are migrating towards the bottom of the puck, creating a barrier to the flow. Turns out, there is not much need to help the process. At least, according to our current ideas.

This reminds me of the idea of putting the portafilter/filter basket on a vibration table to settle the grinds in the basket. I've never tried this, but it would seem that doing this would naturally result in the fines and the bottom and the coarser particles at the top.

On the other hand, if you adjust the grinder from fine to coarse while grinding, you'll still get fines, maybe even more fines along with the coarse particles but your target grind size will increase towards the top of the basket.

Coffee waste would be tremendous on a grinder that adjusted during the shot. It would have purge a gram or few to clear the coarser grind from the end of the previous shot.

When hopper dosing, the first 2 or 3 shots vary every morning due to stales from the day before.

another_jim wrote:When you turn on the pump for a shot, and before the espresso comes out, the fines are migrating towards the bottom of the puck, creating a barrier to the flow. Turns out, there is not much need to help the process. At least, according to our current ideas.

I've always wondered whether this is just an assumption or something we know to some certainty? Any support for this idea?

I know the longer I low-pressure preinfuse, the faster the flow. Shots with no preinfusion are very much slower flowing no question about it. I know this is used sometimes to explain fines migration, but is there other things we know that support this idea?

I once stopped shots at various points and sliced the puck into sections and brewed them. Early in the shot, the lower sections of the puck actually brewed stronger than the regular coffee, since solubles had migrated own from the top layers and not gone into the cup.

The literature reports many experiments with results along these lines. This leads to a model of percolation where solubles and fines travel along the flow path, being reabsorbed and re-emitted by the coarse particles along the way.

I have observed that commercial lever machines require finer grind levels than most pump machines, and assumed that this was due to the long preinfusion times. I'm glad you've observed the same thing and can confirm. However, I'm not sure how this can be explained in terms of fines or solubles migration.

another_jim wrote:I'm not sure how this can be explained in terms of fines or solubles migration.

IIRC, the explanation I read said that fines would get more time to "puff" with longer PI times thus becoming not as small anymore and wouldn't migrate much. Now that I think about it, I'm questioning if fines can actually absorbs water when irrigated and puff?

On second thought, I think what I read was about bigger coffee grinds puffing and trapping fines, and not what I wrote earlier.

The second one makes sense ... if it's true. I suppose I can do more espresso interuptus and send the pucks to John for his SEM.