Pressure profiles, preinfusion and the forgiveness factor - Page 2

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swines

#11: Post by swines »

I understand the fun of being able to quantify an item's performance. However, I'd like to know exactly how you think this information can and/or could be applied to making better espresso?

Can you relate the pressure ramp-up characteristics to better taste? If so, what or how does that mechanism work? Measurements for measurements sake are often interesting, but you can turn it into pseudo-science which then resembles the following for usefulness.


http://www.improb.com/airchives/paperai ... ansas.html

DavidMLewis

#12: Post by DavidMLewis »

HB wrote:Keep in mind that these measurements are taken with a portafilter that's already full
This could bias the results, since a real puck has an unknown amount of air-filled head space. In the real puck's case, it could be seeing a slower pressure rise because of this, assuming you mean "already full" of water in the quote above.

Best,
David

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HB
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#13: Post by HB »

swines wrote:However, I'd like to know exactly how you think this information can and/or could be applied to making better espresso?
I am not asserting that a particular pressure profile is superior, only that they are different. Previously I had assumed that a slow pressure rise would be more "forgiving," but I'm no longer convinced such a blanket statement is justified. However, the pressure profile does appear to influence the best techniques for a given machine. For example, the uber fast pressure rise of the Elektra A3 will punish overdosing by increased channeling; this isn't true for other machines like the La Marzocco. My theory is that the grouphead design is behind these differences, not the pump pressurization speed.

The case for temperature measurements has more practical application. I principally use this information to learn the machine's performance characteristics more quickly. How much to flush if the machine has been idle for 5, 10, and 30 minutes? Generally the first shot or two will run sour if the group isn't heated sufficiently. So how many flushes are necessary to warm it up? How much does the group temperature change, if any, when steaming and pulling shots at the same time?

That's a sample of the questions this sort of data helps answer. Of course you have to confirm what the graphs say with the actual taste. I agree with you, these measurements are not good predictors of the quality of the espresso. They are helpful leading indicators of consistent performance, but I treat them as suspect unless there is weeks of actual use to support the assertion that a machine has a "good" temperature profile.

(Not that I'm convinced there is such an animal. Slant L or humped temperature profile? I'm unpersuaded either is superior for all machines and all blends; holistic comparison is really what matters, the rest is engineering data to support what your tastebuds already concluded.)
DavidMLewis wrote:This could bias the results, since a real puck has an unknown amount of air-filled head space. In the real puck's case, it could be seeing a slower pressure rise because of this, assuming you mean "already full" of water in the quote above.
I absolutely agree. My original motivation for this experiment was to determine if the Elektra A3 had a preinfusion cycle comparable to the E61 expansion chamber or other means for slowing the pressure rise as some offline discussions had suggested. Based on watching how quickly the initial beads formed (around 3 seconds), I didn't think so, but couldn't resist a high-tech way of confirming. Apparently the Elektra designers didn't think a slow pressure build-up was crucial, and judging from the quality of the extractions, I believe they're right.

From the thread Rotary pump cup clarity achievable with a mod ?
AndyS wrote:Dan, what is it about the A3 that made its "preinfusion" different from the others?
and this thread:
HB wrote:Or offer what you think might be other key contributors to the forgiveness factor?
AndyS wrote:Physical factors in the grouphead (headspace above and below the dispersion screen, water spray pattern, etc).
I recall that you added a preinfusion cycle to your heavily-modified Silvia. Based on these results, I wonder if modifying the grouphead itself to increase the space above the dispersion screen would improve Silvia's forgiveness factor? Interested in machining a few channels in the grouphead in the name of experimentation?
Dan Kehn

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AndyS

#14: Post by AndyS »

AndyS wrote:Physical factors in the grouphead (headspace above and below the dispersion screen, water spray pattern, etc).
HB wrote:I recall that you added a preinfusion cycle to your heavily-modified Silvia. Based on these results, I wonder if modifying the grouphead itself to increase the space above the dispersion screen would improve Silvia's forgiveness factor? Interested in machining a few channels in the grouphead in the name of experimentation?

No problem sir! I'll turn her upside, fill the group with conc. nitric, and let her sit for a day.

In the name of experimentation, sir! :wink:
-AndyS
VST refractometer/filter basket beta tester, no financial interest in the company

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HB
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#15: Post by HB »

Funny guy. OK, maybe that is a lot to ask. How about this: Would you explain how you modified Silvia to add preinfusion, and whether it improved her forgiveness factor? Both Mike and I were reminded of Silvia's fussiness during the PID'd Silvia versus Brewtus comparison and attributed Brewtus' better showing to the E61 expansion chamber. Now I'm thinking that's an overstated value.
Dan Kehn

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AndyS

#16: Post by AndyS »

HB wrote:Would you explain how you modified Silvia to add preinfusion, and whether it improved her forgiveness factor? Both Mike and I were reminded of Silvia's fussiness during the PID'd Silvia versus Brewtus comparison and attributed Brewtus' better showing to the E61 expansion chamber. Now I'm thinking that's an overstated value.
Dan, as you know, the word "preinfusion" is tossed around a lot, but everyone uses it differently.

Years ago I put in a time delay relay that allowed the 3-way to open for a few seconds before the vibe pump came on. The coffee would get "preinfused" by the boiler vapor pressure. Damned if I know if that made her more forgiving. I didn't notice any difference at the time, so I took the relay out.

Sometime later I installed a rotary pump, and then a ways after that, a needle valve to regulate the time it took for the extraction to come up to full pressure. With the valve wide open, it would only take a second or two. With the valve tightened, you can control it so that that it takes 3 seconds, 5 seconds, or whatever. That way, I could get a "gradual infusion."

Some call this "preinfusion," others don't.

I think that the extractions are more forgiving when the rampup takes 4-6 seconds as opposed to 1-2 seconds. I think the 1-2 second extractions go blonde sooner. But I would caution that this applies to my machine, with its particular group head design. Other group head designs may perform differently.

And as I told you on the phone today, the REAL interesting part of this is that there's a significant difference in the grinder setting required to maintain 25-30 sec shot timing between the fast and the slow rampups. And the fast rampup requires a <gasp> COARSER setting, by about one notch on the Mazzer Mini collar. Presumably this is because the fast rampups slams the crap out of the coffee cake, compressing it like a 500lb gorilla tamp.

Again, this phenomenon occurs on my particular machine. Barry Jarrett could not duplicate this effect on his LM, but Rene confirmed it on a Reneka Techno.
-AndyS
VST refractometer/filter basket beta tester, no financial interest in the company

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HB
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#17: Post by HB »

HB wrote:As a practical matter, vibration pumps are "slow" to move water compared to a rotary pump, even at no resistance and even slower once there is resistance. Rotary pumps have much much higher flow rates independent of the resistance that you see almost instantaneous pressurization.
I've never had two essentially identical machines except for the pump type to test - until now. Chris Nachtrieb agreed to loan us a Quickmill Anita for EspressoFest (the group, boiler and pump are the same between the Anita and Andreja). Putting the Anita and Vetrano under the close scrutiny of Sean Lennon's pressure profiling kit (thank you Sean!) produces the charts below:

Image
Two E61 espresso machines, two different types of pumps

Anyone care to guess which one is the rotary pump E61 (Vetrano) and which is the vibratory pump E61 (Anita)?
Dan Kehn

lennoncs

#18: Post by lennoncs »

Right=Anita

Sean

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HB
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#19: Post by HB »

lennoncs wrote:Right=Anita
Sorry Sean, left = Anita, right = Vetrano. I was surprised too, but looking at the earlier profile of the Brewtus' vibratory pump, it's almost exactly the same curve. My guess is that the rotary's faster flow rate is producing the very distinct expansion chamber "knee."
Dan Kehn

lennoncs

#20: Post by lennoncs »

Doohh!

Interesting, I would have thought the lower volume of the vibe would have shown a knee.

should have looked back at my own curves too...they show the same thing, now that I am actually looking at the slope.


Neat


Sean