AndyS wrote:David, if I understand you correctly, you're NOT saying that the gicleur produced the bitterness, but that the on-off-on preinfusion cycle produced the bitterness. Yes?

Any further thoughts on how the gicleur affected things?

Hi Andy,

Without the gicleur, the preinfusion seemed necessary to reduce the frequency of channeling if I wasn't quite careful. With it, and the resultant longer dwell times, the preinfusion causes the bitterness. That may be due to the fines getting a chance to overextract before the pressure migrates them into a cake or out of the basket altogether; I also seem to get a similar bitter edge if I rap the portafilter to settle the grounds before tamping, suggesting again that at least with my machine and grinder I'm generating fines that are best moved out of the way. The gicleur seems a definite plus on this machine for lots of practical reasons, and the espresso seems to me to be a bit smoother as well. As you know, when you change one thing, it often means altering other parts of the system or practice to get the most out of it before you can judge whether it's helped or not. This is the sort of thing that makes science so hard for people who attempt to actually learn something from it.

Best,
David

another_jim wrote:I'm not sure how much difference gicleurs versus E61 pressure cylinders versus line pressure, no pump preinfusions make. But I think there might be a simple water volume difference between groups. E61s in all their versions have a lot of volume between the 3 way release point and the top of the puck, whereas the Silvia and little Elektra groups do not.

Seems like that's the utility of Al's "water debit" measurement, it takes the water volume differences into account.

another_jim wrote: I don't know about other groups. A classic E61 has around 10 seconds of dwell time; but it could be a lot of that is just taken up filling the various nooks and crannies in the group; and that the actual puck-absorbing-water time is about the same as in other groups.

Hard to imagine that an E61 with a rotary pump couldn't be set up for a lot less than 10 sec dwell time. But I have almost zero experience actually doing this.

DavidMLewis wrote:Without the gicleur, the preinfusion seemed necessary to reduce the frequency of channeling if I wasn't quite careful. With it, and the resultant longer dwell times, the preinfusion causes the bitterness.

Perhaps the gicleur plus the extra preinfusion cycle provide something like a preinfusion on top of a preinfusion, which throws the shot out of whack.

DavidMLewis wrote:Hi Andy,

Without the gicleur, the preinfusion seemed necessary to reduce the frequency of channeling if I wasn't quite careful. With it, and the resultant longer dwell times, the preinfusion causes the bitterness. That may be due to the fines getting a chance to overextract before the pressure migrates them into a cake or out of the basket altogether; I also seem to get a similar bitter edge if I rap the portafilter to settle the grounds before tamping, suggesting again that at least with my machine and grinder I'm generating fines that are best moved out of the way. The gicleur seems a definite plus on this machine for lots of practical reasons, and the espresso seems to me to be a bit smoother as well. As you know, when you change one thing, it often means altering other parts of the system or practice to get the most out of it before you can judge whether it's helped or not. This is the sort of thing that makes science so hard for people who attempt to actually learn something from it.

Best,
David

I'm of the opinion that pre-infusion styles are good to have in one's bag of tricks. My results with George Howell's Brazil Daterra were best with no-pre-infusion at all, but with 0.6mm gicleurs installed on my LM Linea. My usual diet of dry-processed Ethiopians (that's swearing in George Howell speak) seem to like relatively low pressure pre-infusion, followed by fairly quick, but smooth ramping to full pressure.

-Greg

another_jim wrote:The original group had an adjustable tensioner for the preinfusion spring. I'm sure in Italy they have an assortment of springs and jets to get whaever the barman wants.

Requirements for spring assortments etc depend on the volumetric flow rate supplied by the pump, of course.

-Greg

i find it interesting how there are so many of these interesting tech discussions that take place but its rare to see anyone talk about what counts - results!

so, lets summarize:
-we know we can flow fast, or flow slow.

-fast flow with a fast ramp will cause a lot of extraction. im assuming it (the shot) will also blond faster, and taste more acidic.

-slow flow with a slow ramp will produce the least amount of extraction. im assuming this will cause over extraction and a bitter taste.

-more preinfusion can be bad. (this is most easily on a lever machine imo. this isnt a tea bag, we dont need to steep the coffee! lol)


so, where does this lead us? what TASTED better? i cant serve graphs to my guests.
on my machine, varying pump pressure, boiler pressure, flush time and grind does a minimal amount to change things.

i think each machine has an inherent design that its meant to maintain, regardless of how we try to change some parameters.

AndyS wrote:Last time the results suggested that increasing pump pressure above ~8 bar actually decreased the extraction rate, and I wanted to verify this result.

I have experienced this when I really crank down on a lever machine, and it appears others have as well, as discussed on this thread: http://www.home-barista.com/levers/how-does-la-pavoni-professional-compare-to-silvia-t4847.html
along with some interesting remarks on preinfusion that seem germane to this discussion.

Alchemist wrote:Here is my take on pre-infusion. I am a organic chemist, run HPLC columns, have packed probably hundreds of low pressure resin columns, and conditioning (pre-infusion) of your matrix is positively what you do. No if ands or buts. If you don't you get a collapsed bed, channeling, and generally crappy elution results. The puck is nothing more than a short HPLC column where water is your eluent and the soluble solids are your analytes. If you don't pre-condition your column, you don't have a chance of consistency and quality day in and day out.