Temperature, Pressure, and ...?

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MJW
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#1: Post by MJW »

In one of the Bench articles about the Lusso, Dan made a comment in the context of the Elektra's temperature curves that were reported by Jim.
On plotted paper, the Elektra looks more like a $200 Krups than a $2000+ wonder espresso machine. Its cup results are consistent and undeniably good to very good. In an offline discussion, Greg remarked that brew temperature and brew pressure are only two metrics of more than a dozen that are proven to significantly affect the cup. [...]
I'm curious about the metrics Greg refers to, especially any such metrics that cannot be derived from the temperature and pressure curves.

Presumably like everything else these metrics have been discussed to death at some point in the past; anyone have any pointers to previous discussion? Thanks in advance.

jonr
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#2: Post by jonr »

I would distinguish between brew temperature and pressure (single number for each as seen in the quote) and brew temperatures and pressures (ie, full profiles over time). The former are definitely not sufficient metrics for a machine.

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[creative nickname]
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#3: Post by [creative nickname] »

There has definitely been discussion, in various threads, about the perceived differences between different pressure-production systems. Vibe pumps, rotary pumps, and mechanical levers all move water in different ways, which might account for taste variations between these machines.

Basket diameter and depth has also been discussed as an important variable; some owners of small home levers (me included) think that their small baskets, filled with a deeper column of coffee, are more forgiving of small variations in grind size that would produce shot defects on a pump machine.
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another_jim
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#4: Post by another_jim »

When you take pressure and temperature measurements, you measure one spot of the machine or basket. This is true even if you are graphing that spot over time. If the rest of the puck is doing something very different than the spot you are measuring, your measure is not a good estimate of what is happening over all. Moreover, if there is a great deal of random variation in what is happening in the puck, the shots are not going to be very controllable or consistent.

The Elektra Semi is not a particularly precise machine in terms of temperature or pressure. But the group head design goes to extraordinary lengths to make sure the entire puck is getting exactly the same treatment. So if you pack and distribute the coffee properly, you will get consistent shots. This is is also true of all lever machines; a puck sized column of water directly over the puck does that automatically. But it is not necessarily true of pump machines, where the water is fed to the brewing zone over the puck through relatively narrow tubes. Here, the way the water is dispersed as it enters the brewing zone is of critical importance. Some group designs do it very well; others do it very poorly.

If you don't grind, dose and pack the puck well, you get uneven brewing. A group with poor water dispersion brews just as unevenly as a poorly prepped puck. You can add pressure profiling, PIDs, double boilers and all the other bells and whistles, you can have it ace every measuring test in the world; and the shots will still be screwed up.
Jim Schulman

jonr
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#5: Post by jonr »

another_jim wrote: If the rest of the puck is doing something very different than the spot you are measuring, your measure is not a good estimate of what is happening over all. ...you can have it ace every measuring test in the world; and the shots will still be screwed up.
Measuring and comparing multiple positions in the puck is easy enough to do. Do you have any data to support that such variations occur and are significant?

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erics
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#6: Post by erics »

Measuring and comparing multiple positions in the puck is easy enough to do.
I disagree. It is time and $ consuming, not to mention some fabrication skills that few possess.

And then, to what end? The temperature of the water presented to the coffee is a very reasonable benchmark.
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another_jim
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#7: Post by another_jim »

jonr wrote:Measuring and comparing multiple positions in the puck is easy enough to do. Do you have any data to support that such variations occur and are significant?
It would require a grid-like mesh of pressure and temperature sensors at various levels of the puck, with measures reproduced over several different machines, to understand the effects of water distribution on flow through the puck. If this is easy enough for you; I'd be delighted if you did it.
Jim Schulman

jonr
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#8: Post by jonr »

If the rest of the puck is doing something very different than the spot you are measuring
Sounds like an unlikely and unsupported theory, at least in terms of machine design. Basket shape and tamping technique sound like more likely things to cause flow variations across the puck.

MJW (original poster)
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#9: Post by MJW (original poster) »

Jon given your accomplishments with the Gaggia I bet if Quick Mill sent you a thermoblock we'd have a nice advance in espresso machines within a month!

What about computer simulation? At first, this doesn't seem like a way to evaluate existing machines. But, in principle one could carefully model the MCAL's geometry & materials, and attempt to simulate what the water is doing. Probably there is chaotic behavior, and the simulation may only be good for a qualitative understanding that could lead to better or cheaper designs, rather than an exact characterization of the machine.

jonr
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#10: Post by jonr »

Thanks. It will be interesting to see how well ZPM does with computer control of their thermoblock. Given that it has mass and flow can vary quickly, precise temp control sounds challenging.

I suspect that you are right about simulation.

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