Pressure profiles, preinfusion and the forgiveness factor - Page 2

[mteahan]

Dan,

Why is the rapid ramp up of pressure problematic (potentially) for the Elektra yet not so with the Marzocco? The GS with PI won't channel if used properly, but the Marzocco is inefficiently jetted and is one of the most sensitive machines to espresso pack density and quantity I have ever encountered. I am tempted to credit the infatuation with tamp style and process with the inherent unforgiving design of the LM head. The jet on my GS is a crimped copper tube--not very exact.

??

Michael

[HB]

Why is the rapid ramp up of pressure problematic (potentially) for the Elektra yet not so with the Marzocco?

That was my original point: I assumed that rapid ramp up of pressure would be problematic based on my experience with E61s. The experiment documented in this thread says to me that quantifying the forgiveness factor isn't as simple as plotting a pressure profile.

I have some limited experience with La Marzocco commercial equipment thanks to Counter Culture Coffee opening their espresso lab to the public every Friday. They twiddled with the gicleur diameter on their machine and I noticed an improvement in the forgiveness factor (though not everyone agrees on this point, as noted in The problem is on the handle side of the portafilter). I think the extended dwell time introduced by a smaller gicluer and Andy's suggested contributors ("Physical factors in the grouphead (headspace above and below the dispersion screen, water spray pattern, etc).") are more important than the pressure profile.

[mteahan]

Nothing is as simple as . . . . anything really.

The pressure profile must take into account the jet (gicleur). While this affects the ramp up pressure in the head, it is more a flow issue. Once the backpressure develops in the portafilter, the jet has little effect on applied pressure. Only a PI system can maintain a lower initial PI pressure as the puck begins to saturate with water.

My experience has been that mechanical PI systems are more forgiving, and decreasing the jet size will encourage a PI effect on a Marzocco. Marzoccos have usually been prone to flood the portafilter very quickly, which is the probable cause of inconsistencies with the Marzocco system. Decreasing the size of the jet helps, but since it was never designed to thermo-compensate, fiddling with the jet should be in conjunction with a temperature evaluation over the brewing cycle to make sure nothing changes. If the jet is sufficiently downstream, it won't, but I don't recall where the jet would be on a Marzocco.

What we think we know about brewing espresso is based upon a series of assumptions that go back so far, no one can recall the origins. Much of the work here and with many of the home users is testing the foundations of those assumptions, which is refreshing. Ken's work with his Cimbali Jr. is very cool; and not just because it re-enforces the theories I have held for quite a while.

If we can begin to test without these pre-conceived notions of what is necessary to evaluate a machine, that would be really interesting.

Michael

[AndyS]

If we can begin to test without these pre-conceived notions of what is necessary to evaluate a machine, that would be really interesting.

To what preconceived notions do you refer? Can you be specific?

[barry]

If the jet is sufficiently downstream, it won't, but I don't recall where the jet would be on a Marzocco.

on the inlet fitting at the neck, although the banjo bolt can be bored and tapped for one, too.

[Jepy]

Anyone ever used this one Marzocco group?

[lino]

I'm no expert, but that looks a little like a preinfusion chamber...

And, no, I haven't used it.


ciao

lino

[Jepy]

Maybe it was going to be their answer to the E61 pre infusion style. I wonder if it ever made it off the drawing board

[lino]

That also sure looks like the hard way to load the PF handle...


ciao

lino

[Jepy]

It says patented in 1997. I wonder if the PI chamber had an effect on temp stability.

[malachi]

That also sure looks like the hard way to load the PF handle...

I totally missed that at first! Very funny. Wonder if the drawing was done by one of the folks in the ESI parts dept...

[lennoncs]

...Wonder if the drawing was done by one of the folks in the ESI parts dept...

When I had a patent drawing done, the drawing conventions set forth by the patent office are still based on pen and ink illustrations done 100 years ago....it was so bizzare seeing a modern carbon fiber part rendered in that way.

[hbuchtel]

Dan, would it be possible to hook up all this equipment to your Lever machine?

It would be really interesting to compare the ramp up of pressure to the other types of pumps.

Henry

[HB]

Lino and I have discussed this possibility for his Peppina since it has all the requisite fittings:


From Has anyone ever PID'd a lever machine?

Measuring the ramp up pressure of a lever machine against a blank portafilter would only be mildly interesting (I would expect to see an initial pressure around the same as the boiler pressure, then nearly straight up to max pressure). Neither Steve nor I have volunteered to tap the grouphead our respective Olympia Cremina / Elektra Microcasa a Leva in the search of the truth, however he did offer a close approximation in Olympia Cremina 2002: The evolution of design using an ordinary bathroom scale:



Of course this trick wouldn't work for the Microcasa, but presumably one could guesstimate the pressure profile by measuring the brew pressure at the top and bottom of the spring's travel. As I recall Lino's mechanical calculation, the Microcasa's spring is capable of putting out around 6 bar and tapers off to around 4 bar. A lot less than I would have expected.

[Jepy]

I've been using this as my at the group pressure reader. Not a cheap gauge, but worth it, as I 've measure some of the quality cafes around here and seen that the Marzocco gauges are reading higher than this devise. Which brings up another point. As we get more and more into pressure profiling, and studies, when can we do away with the "Bar" measurement? Or at least use it after reading in PSI first. 14.7 PSI per Bar, just a whole lot easier to read small amounts.

John

[barry]

14.7 PSI per Bar, just a whole lot easier to read small amounts.

nope. 14.508 psi/bar

[Jepy]

nope. 14.508 psi/bar

Oops, sorry. I guess I should proof read, You get my point though, smaller increments....

[AndyS]

Oops, sorry. I guess I should proof read, You get my point though, smaller increments....

Don't get your point. Who cares whether the measurement is 134 psi or 9.24 bar? Since everyone's been using "bar" for years, why change now?

(image of Mirage Idrocompresso)

[Jepy]

It's not that I care what the numbers are 134 Vs 9.24(grey arrows), visually it's easier to read from the gauges I've found. I've been profiling my pressure for a while now, and seen how different coffees sweet spots can differ if only slightly. For example(subjective of course)Hairbender, pre-infusion 19 psi top pressure of 127psi Vs. Lighthouse Roasters Espresso blend pre-infusion again at 19psi, but tops out at 122. Both of these also have a ramp down pressure.

The pictured gauges are of similar pressure ranges, all marks should be roughly the same. What would you rather be reading from? I've cataloged quite a bit of data on different profiles for different blends, and wouldn't go back to bar myself. Next I'll be using the computer to data log, but still like to have the analog visual of my gauges.

John

[battlecry]

I just finished installing a (wet) pressure gauge on the Silvia with a few loops of copper tubing to reduce the line pressure variations and provide some thermal isolation for the gauge. It hit me that, except for the thermal isolation and protection of the gauge, maybe I should have installed the copper coil just downstream of the pump, before the boiler, so as to provide a damping effect to the complete brew apparatus, not just the gauge.

Would such a coil, or perhaps a water-hammer type damper, provide a steadier pressure rampup and brewing pressure profile?