Preamble:

The Ponte Vecchio Lusso was one of the models tested during the Lever Espresso Machine Smackdown and the only one with a themosyphon design. The others (Olympia Cremina, Elektra Microcasa a Leva, La Pavoni Europiccola) bolt the grouphead directly to the boiler. I've owned the Microcasa and Cremina for years and am well familiar with their thermodynamics. The Lusso's thermosyphon design is well known among E61s, but unique among small lever espresso machines. I was curious how well it worked with such a small machine and 1st-line agreed to source a custom 43mm thermofilter from Greg Scace so we could explore it more fully as part of the Buyer's Guide.

Questions:

The thermofilter proved to be very helpful in refining the brew temperature protocol for the Lusso. In addition, I wanted to answer questions like:

1. The Lusso idles cold. What's the optimal flush amount before brewing?
2. After pulling a shot, how long before the brewhead cools enough to again act as a heatsink / thermal dampener?
3. What techniques could be employed to reduce wait time between shots?
4. Can flush amounts / delays be manipulated for more precise brew temperature?
5. How capable is the Lusso of "on the fly" repeatable brew temperature manipulations?

My inquiry began with the second question, how long must I wait between pulls before the grouphead is "ready" again, assuming no tricks like applying cool towels or locking in a cold portafilter. The video below captures my first confirmation that 3 minutes is the Lusso's natural rhythm:



As you see, the peak temperature is around 206 each time. Consistency is certainly good news; My other two levers would rise with each pull until the water flash boils immediately upon exit. But what about the water temperature rising so high above the desired brew temperature of ~201? Wouldn't that assure a bitter, burnt espresso?

Espresso imponderable:

Prior to the thermofilter's arrival, I had already gotten to know the Lusso quite well. It certainly didn't seem to run hot. When it took the road trip to Counter Culture one Friday morning for an informal side-by-side with their La Marzocco WBC three group, no one's comments even hinted at bitterness. Several attendees expressed surprise at how good the Lusso's espressos were (comments like tasty, smooth, good flavor, etc.).

I enjoy a good espresso imponderable. While it wasn't a mad obsession over the following months, I wanted to better understand why a small, unassuming working-class lever espresso machine avoided the brew temperature machinations of its far flashier cousins. Over the next two weeks, I'll share my thoughts and welcome your explanations of this espresso imponderable.

Background information:

For the benefit of those new to the group designs of these lever espresso machine designs, here's a brief recap:

For all of these espresso machines discussed in this post, the boiler is under steam pressure of approximately 1.0 bar, thus the water boils around 250 degrees Fahrenheit instead of the usual 212 at sea level. Subsequently the water must be cooled to brew temperature by the grouphead acting as a heat sink. But even if not brewing an espresso, the Cremina/Microcasa/Europiccola espresso machines will overheat when idle, simply by the conduction of heat from the boiler to grouphead. There are various tricks one can employ like wrapping a cool towel around the grouphead or locking in a cold portafilter to reduce the grouphead temperature. A thermosyphon design separates the grouphead and boiler; two thin pipes run from the boiler to grouphead and the difference in temperature of the water in the upper (hotter) and lower (cooler) leg of the loop creates a siphoning effect, drawing the water from the boiler to the grouphead and back. Because no thermosyphon is 100% efficient and because the grouphead radiates heat itself, the effective grouphead temperature is approximately the desired brew temperature. The length and diameter of the upper/lower legs of the thermosyphon loop can be changed to increase or slow the speed of the water circulation, which increases or decreases the effective grouphead temperature. While not directly applicable to the Lusso, the discussion of the thermosyphon of E51 espresso machines is presented in How I Stopped Worrying and Learned to Love HXs.

hbuchtel wrote:In addition to the Scace measurements, are the following possible or planned?

At some point, yes.

timo888 wrote:I'm not sure what the device is measuring. Water temperature? Metal temperature?

If the probe is measuring the temp of the water in the piston chamber .... the water in contact with the metal may be cooler than the water that is not. Or is it measuring temp directly above the puck, below the shower?

You can read about the thermofilter here. The thermofilter I used is a smaller version of the one below:

How long does the lever handle remain in the down position when you fill the chamber?

As shown in the video, not long at all. In actual use, I preinfuse for 3 seconds.

How long is the timeslice of the max-temp reading? That is, if the temperature reaches n degrees for a nanosecond, does that temp become the maximum reading? Or does the temperature have to be steady for several seconds in order to register? Is there a way to adjust (lengthen) the timeslice?

The Fluke 54-II shown in the video is quite sensitive; the max reading timeslice is probably less than 1/2 second. I recorded the readings, but haven't plotted it out since it's an obvious U-shaped curve.

Preinfusion aside, the Lusso will be operating at ~7 bars I think. So the lower pressure, vis-a-vis 9+ machines, has an ameliorating effect upon the temperature.

We measured a maximum pressure of 6 bar trailing off to 4 bar, consistent with other home spring lever espresso machines. Good point about the brew pressure/brew temperature relationship, it's worth investigating further (e.g., using Greg's rotary pump with programmable pressure profile).

peacecup wrote:Can't that be done with a full portafilter? The water would be filling the grouphead, which is designed to sink heat. As it is now its basically coming from the boiler and hitting the probe.

Granted, that very upper layer of the puck will be hit by that hot water, the remaining water in the piston chamber will be cooling to under 206, and probably right down to the optimum range.

It's a common misconception that the thermofilter simulates a coffee puck (the same point came up during the review). That's not its purpose. Greg designed it to measure the consistency of the brew temperature, and in that regard, the Lusso performed quite admirably. Measuring the puck's "brew experience" is more difficult. Where do you place the probes? Can your readings be compared to mine? The thermofilter measures the water temperature at precisely the same location below the dispersion screen. It's a great tool for optimizing your routine, but its readings should not be strictly interpreted as the actual brew temperature for the reasons Tim cited, among others.

Can you get 1st-line to send you an Export to try also? I'm convinced that the PV group design is a better heat sink than are the other standard home levers. It would be very useful to test the direct-connection Export, because it has a lot of attractive features (portability, easy empty-boiler, lower price) for those of us who don't often brew for large parties.

I asked at the time the Lusso was shippped, but Jim didn't have one to spare. I will ask him again, though no formal buyer's guide for the Export is planned.

Timo,

That's an interesting question. I've never used a spring-lever before, but it seems like if you were making a normal shot you would hold the lever down more than Dan was in the video with the thermofilter, and I would expect that time would definitely mitigate that high-temp water from penetrating the puck the way it does there.

In any case, it sounds like a moot point. As Dan says, the thermofilter is for verifying consistency rather than drawing conclusions about temperature profiles during actual brewing. The Lusso wins big time there, and the cup results indicate that that 206F spike is either not there, or it doesn't negatively effect the cup--so whether it's there or not is not likely to actually matter, is it?

I agree, brew temperature reproducibility is an important contributor to exceptional espresso, but I've yet to see any blind taste tests demonstrating the superiority of one profile over another. Jim's writeup of the Elektra Semiautomatica drove this point home:


From Elektra Semiautomatica - Appendices

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 find the thermofilter very helpful for shortening the learning curve, but I treat the temperature plots it helps create as something to offer insight into why a particular espresso machine performs well, not predict that an espresso machine will perform well.

Yes, the boiler pressure is around 1.0 bar. The factory setting was 1.5 bar, which is probably in line with the brew temperatures you want. It was too hot for the coffees I use. Another possibility is to flush the group to raise the grouphead temperature for an on-the-fly adjustment. I haven't measured, but my guess is that a hard 3 second flush just prior to the pull would do it. For my usage, a very short half flush and then a minute delay for stabilization works best if the machine was idle; otherwise it's no more than a spritz to knock off the grounds, then lock, load, and pull without a delay.

timo888 wrote:At 1.1 bar or higher, if the thermosyphon is flushed once when the false pressure has been dealt with during initial heatup, the Lusso will idle at-temp, not cool.

As noted in the video credits, the boiler pressure was 1.1 bar for these measurements. BTW, how did you measure the brew temperature? Not that it makes a lot of sense to speak of "idles at temperature" when the brew profile is shaped like an inverted U.

timo888 wrote:If you do not purge the thermosyphon with a brief flush (an ounce will suffice) after the false pressure has been bled at startup, the Lusso's group will remain near room temperature even after a couple of hours.

I've never observed the Lusso's group remaining at near room temperature without an initial brief flush. I don't recall any of the other Smackdown participants mentioning it either. Maybe it is unique to your machine? We heard a few similar reports of thermosyphon stalls among Vibiemme owners. I don't doubt the reports, but I was never able to reproduce the problem.

When you say the Lusso "idles cold", are you speaking literally, i.e. referring to the room-temperature group and the need for a thermosyphon purge?

What I meant by "idles cold" is that the grouphead temperature drops to ~150F measured with a thermofilter (as shown in the video). Other machines I've measured in a similar manner idle around 185 to 195F. I haven't read the patent yet, but I assume the Lusso's cold nose design intentionally counterbalances the over-temperature steam boiler water during an extraction. After a long idle period, I find the Lusso performs best if it's given a short flush and then allowed to stabilize for a minute or so.

I measured that with my tongue: walked up to the machine after a few hours and directly pulled a tasty espresso with no warming flush.

Sorry, that doesn't match my experience. I used the Lusso for months without temperature measurements and the taste of the first shot exhibited classic signs of low brew temperature (sour taste, lighter crema color). This was later confirmed using a custom thermofilter. It takes very little effort to get the Lusso ready for brewing, but its walk up and pull brew temperature is too low for the blends I use.