I've posted several threads about temperature surfing La Pavoni manual lever machines, although I haven't called it "temperature surfing." Essentially with these machines and the similarly designed Olympia Express Cremina, one can partly raise the lever and introduce steam or hot water into the group without infusing the coffee cake. This offers the ability to start at a precise temperature and control the range of overshoot, tuned to a particular coffee, and it can usually be done without adjusting the PSTAT.

So, I was curious about whether I could do that with my Elektra Microcasa a Leva (MCAL). I attached a thermometer to the group that I've acquired for my Cremina and discovered that apparently this can't be done with the MCAL. With the lever depressed enough to introduce water, that water starts pre-infusing the puck. At the most one can do a longer preinfusion to brew hot for a bit longer, but this is nothing like the versatility offered with La Pavoni manual levers or the Cremina. Perhaps one clue to this is the weep hole at the back of the group, which isn't supposed to retain water that isn't flowing to the coffee cake. And, the water that enters the group does so through a dipper tube that draws water from low in the boiler. So this group isn't steam heated.



Here's the thermometer attached in long and close view. I employed a very nice lab clamp purchased on eBay, and used a Taylor 608 "Elite" instant digital read thermometer. I really like adapting this thermometer for reading group temperatures. It's more attractive than the plastic ones. The back pinches off for changing the battery, and removing the back also removes the sheath from the wires on the heat sensor. They're not glued to the sheath. The back of the thermometer also has a button to switch between F and C temperatures. And, it's inexpensive. It took me all of 15 minutes to adapt and attach this thermometer, cutting the metal sheath part way so I could clamp the thermometer on the sheath and have the wires flexible for being held to the group with a portafilter gasket o-ring. I used Radio Shack heat shrink tubing to protect the loose wire of the probe.





I'll leave the thermometer installed long enough to pull successive shots and measure group temperature stability. MCALs have a reputation for the group overheating but in small volume use I haven't experienced that issue. This is probably helped by the Teflon gasket I've installed between the group and the boiler. I'll post more on that soon.

From examining both MCAL groups and diagrams it seems that these groups are heated by conduction through the mounting flange and the short but fairly tall piece of metal between the group and the flange. It is also heated by the incoming water for each shot that is at about 120 degrees whilst inside the boiler. I suspect the MCAL engineers must have either made calculations or experiments to determine exactly how much metal to put in which area so that just enough heat tranfer can occur to balance heat loss.

They seem to have been reasonably successful.

This is really dramatically different from either of the two La Pavoni principles:

The first is the 1961-1973 and post 2001- type. Their heating depends on bringing extra hot water besides the water used for the shot into the group by having a water space between the piston wall and the group wall.

The second is the 1974 to 2000 type. Heating here is brought about by allowing the space above the piston to be always in contact with live steam, keeping the top of these at the boiler temperature.

When any of these designs are executed to make espresso machines there are some very complex parameters. I am not sure that the dimensions and parameters are always right!

Nice addition, Robert.

I see the MCAL as designed for the group to be a heat sink and the boiler to provide the heat. The La Pavoni and Olympia Cremina and similar designs are more complex and can be temperature surfed. Yes, those groups are heat sinks but the water or steam in the group provides more versatility and perhaps more heat "instability" to those who don't figure out how to use that to their advantage.

Well some of this due to two other design constraints on the Elektra, the most important being that the spring has to go somewhere and the second being that a piston with lower mass will hold less heat.

The cavity on the Cremina certainly allows you to speed warm-up at the beginning of the day and allows some temperature surfacing, though I'm not convinced it makes a big difference to the so-called overheating issues (which can generally be "overcome" by an appropriate pressure stat setting and somewhat less hasty approach to life). I am certainly very sceptical of any claims that the two small channels create any significant thermosyphon effect.

Hi Michael:

Not quite sure what you are saying about the thermosyphon effect. With Pavoni and Cremina I'm pointing toward the ability to keep the temperature in check with a moderate PSTAT setting (or toggling switches on a Pavoni without PSTAT). This means some half pumps can be used to bring the group up to brew temperature and a variety of coffees can be made in a row. If you've got a favorite coffee and have your P or C's PSTAT optimized for that, you can walk up and pull a shot without much fuss, no half pump needed -- assuming one has followed Robert's early instructions to purge air from the machine.* As far as cooling the group goes, yes a reasonable pace of living makes overheating less of an issue or modest cooling efforts should suffice if the PSTAT isn't set high.

I'll digress off topic for a bit and then get back on topic.

In general I'm thinking about how to more easily control temperature on home levers so there are few sink shots. I feel I've achieved this with the Pavonis I've tried (1990 and Millennium) and Cremina using group thermometers. I'm thinking about how to do this with the MCAL and machines of similar design, even commercial levers. With the latter temperature is mainly controlled via regulating boiler temperature. Where the machine has a PSTAT that's hard to get at this can limit choice of different coffees one samples in a row.

For a machine where the main point of control is the boiler and where the PSTAT isn't easily accessed, I'm thinking the most convenient control system may be a PID, simply for the ability to dial in a number. So the PSTAT becomes an added safety feature and it's set relatively high. The PID is used to regulate temperature and doesn't need heroic mods to be put into use. For instance I've found some plug and play units where I may attach the probe to the outside of the boiler and correlate that temperature with the desired manometer reading. The machine gets plugged into the PID, which turns on and off to get to desired temperature. I'm remembering how much the PID eased temperature settings on my single boiler Isomac Amica E61 machine.

Back on topic, for this thread I want to better understand group and boiler temperature on my pre 2005 MCAL, how they relate to each other and can be most easily adjusted for different coffees. I'm going to measure whether my group buffered by a Teflon gasket easily overheats with five shots in quick succession. I also want to measure temperature at the coffee cake versus that on the outside of the group so I can more easily target temperature for the coffee I'm preparing.

* I've added the vacuum breaker boiler cap to my Cremina, which eliminates the need to purge the steam wand. Otherwise see his excellent thread on Dalton's Law.

michaelbenis wrote: I am certainly very sceptical of any claims that the two small channels create any significant thermosyphon effect.

drgary wrote:Not quite sure what you are saying about the thermosyphon effect.

The Cremina has an upper and lower port into the cylinder, which would lead one to think that they might support a thermosyphon action. Michael is right, though - since both ports lead back to the dipper tube there really can't be any thermosyphon action.

In the Cremina and the Pavonis you have water and/or steam (plus initially a little air) above that upper seal, and when you do half-pumps, keeping the piston seals below the chamber's inlet port, you will cause that water/steam to circulate between the group and the boiler, so this is an effective way to heat the group. (In the Gaggia Factory users manual they recommend doing two or three half pumps before preparing the first shot.)

On machines like the MCAL, there is no boiler-fed water/steam above the piston's upper seal - it's just air, and is ported to the atmosphere via that little hole that you see in Gary's picture. So you would expect that half-pumping would not circulate any water or steam between the group and the boiler.

However, on all these machines you can use small open port flushes (you do that before you dose and lock) to bring a group up to the proper temp. That's what I've always done on my Pavonis - it wastes a little water but I think is more effective than half pumps, especially on the millennium. But I infer from Gary's posts that he likes to get the group temp just right AFTER the PF is dosed and locked in, using half pumps. I bet that won't work on the MCAL - but I guess we'll see.

homeburrero wrote:However, on all these machines you can use small open port flushes (you do that before you dose and lock) to bring a group up to the proper temp. That's what I've always done on my Pavonis - it wastes a little water but I think is more effective than half pumps, especially on the millennium. But I infer from Gary's posts that he likes to get the group temp just right AFTER the PF is dosed and locked in, using half pumps. I bet that won't work on the MCAL - but I guess we'll see.

Hmmm...now that's an approach I hadn't considered. I'll have to try it!

With the Millennium I have no problem getting it to temperature with half pumps. The only reason I can see for an open port flush is to have minimal overshoot during a shot, so that's another method to use where a coffee has a narrow brew temperature sweet spot.

With the MCAL half pumps don't work and an open port flush doesn't raise group temp any more than occurs with pre-infusion. The best I could do was a couple of Fellini moves (recocking the lever) at the start of the shot but the temperature rise isn't dramatic there either. This is telling me that brew temperature is governed primarily by boiler water temperature.

Next I'll try multiple shots in a row to investigate any overheating. I'll also put thermocouples on the outside of the group and on the coffee cake to find out how external group temperature corresponds with actual brew temperature. I'll get to these additional tests over the next few days.

Meanwhile I'm enjoying dialing in the MCAL again and will try with the larger booster spring too. During the lever fest last month we compared lever resistance on a new MCAL versus mine and mine was pretty soft even with the small booster spring installed. And then there's a thread where a newer spring is put in an older MCAL like mine and it apparently works.

Measuring Temperature Outside the Group and in the Brew Chamber

For the next phase of this study I removed the group thermometer and attached thermocouples to a dual port data logger, recording that with Artisan roasting software. I keep some undrinkable coffee beans in the freezer for tests like this, so at least their gave their all for a noble cause. I ground five 16 gm doses and tamped them into double baskets so I could pull them quickly in a row without any effort to cool the portafilter in between. Here's how my setup looked. Room temperature was 75F.



Here's a closeup of the TCs attached outside and inside the group.



Testing Five Shots in a Row

I pulled my first shot and someone rang the doorbell for a package delivery (!). That's why you see a delay there. But here's how temperature varied over the course of five quick shots. The red tracing is temperature outside the group, the blue was a thin wire thermocouple threaded over the lip of the portafilter and inserted in the coffee cake. The last temperature rise is from a group cleaning flush. Looking at this graph one would think temperature is unstable. Keep in mind my MCAL has a Teflon gasket installed between the group and boiler to make it more stable than an unmodified machine.



Here's the manometer setting, a bit over 1 bar.



Unaided Temperature Recovery Time

If I pull a shot and let the group recover by itself, it takes several minutes to return to starting temperature where the outside of the group cruises at about 172F.



How My Routine Ensures Temperature Stability

But I never experience overheating. Here's why. When I finish a shot I rinse the portafilter under the sink. This is a stock portafilter with the bottom chopped out. It's not as massive as a Richard Penney portafilter or an unchopped MCAL portafilter. I inserted a filter basket to simulate my usual routine but didn't have any coffee in it. It took about half a minute to return to the prior group temperature. Even if I'd started the shot earlier the cooler portafilter would have kept the shot cooler. For someone pulling several shots quickly without access to a sink, a cup with room temperature water would be sufficient.



Impressions

This brief look at MCAL temperature tells me that I've got a temperature stable machine as long as I rinse the portafilter under cool tap water. Or, if I take several minutes between shots as I often do, no cooling is needed. During an H-B meet-up at my home awhile back, this machine was running and people would occasionally pull shots and it didn't overheat.

I'm a strong advocate of group thermometry with a La Pavoni or Olympia Cremina manual lever. Not so with an Elektra Microcasa a Leva. My results earlier in this thread also tell me it's not worth getting live readings of outside group temperature since this machine can't effectively be temperature surfed (unless one is changing coffee while pulling multiple shots in a row). The best instrumental temperature indication is boiler temperature, as indicated by the manometer. Correlate this with how your coffee tastes and you'll know you've got it dialed in.

This:

drgary wrote: I'm a strong advocate of group thermometry with a La Pavoni or Olympia Cremina manual lever. Not so with an Elektra Microcasa a Leva. My results earlier in this thread also tell me it's not worth getting live readings of outside group temperature since this machine can't effectively be temperature surfed (unless one is changing coffee while pulling multiple shots in a row). The best instrumental temperature indication is boiler temperature, as indicated by the manometer. Correlate this with how your coffee tastes and you'll know you've got it dialed in.

Is only valid if:

drgary wrote:Keep in mind my MCAL has a Teflon gasket installed between the group and boiler to make it more stable than an unmodified machine.

And you space your shots accordingly to let group cool down.

I had stock MCAL and "controlling" temperature without any thermometry is impossible for me. By controlling I mean getting shots brewed with acceptable temperature of about 200F.

That Teflon gasket is really the key. Good information here.