So, there has been some discussion around here lately of the temperature profile on various Pavoni machines. Matt Hoffman has reported that, on his crazily modified second generation Pavoni EP, he could obtain a declining temperature profile with a set of cooling fins attached to the grouphead, but that without it the temperature profile was humped. Gary Seeman, meanwhile, reported that when he measured brew temperatures on an Elektra MCAL, they fell and then rose! All this while I had assumed that, for reasons of pretty basic physics, most lever groups should offer declining temperature profiles, as the cooler group absorbs heat from the water throughout the shot. But clearly things are more complicated -- for one thing, the coffee cake may cool preinfusion water faster than the hotter grouphead cools the remaining shot water---so I decided to do some measurements of my own on my favorite lever, the Caferina.

The Caferina (along with its sister machines, the Co-Fer & the Nea Lux) was the inspiration for the first generation of Pavoni Europiccolas, which is a very popular group design around here there days. It is heavily built, with an internal brass sleeve in which the piston travels, which can be pre-heated by half-pumps of the lever, which move boiler water into the space between the sleeve and the outer wall of the group. So what I'm documenting here should be applicable to at least the first generation of Pavoni machines as well.

In my first few trials, following a similar approach to how I normally pull shots, I observed either a rising-then-flat or a humped profile rather than a flat or declining one. Here's a representative "initially rising, then flat" profile. (If folks would find it easier, I can post pics, but given the limits of the Roastmaster app they are not as clear as one might wish.) For those who use similar equipment, I heated up the machine until it vented, then left the switch on minimo while prepping the basket. I flipped back to massimo, waited for the venting to become vigorous, and then I pull the shot. At that point, the group temp, measured at the side of the bell, was in the high 180s. All temperatures are measured in F.

T0. Pre-infusion begins. Exterior of group (measured at the lower left side) is at 188F.
T=10s. Pre-infusion is complete. Exterior Temp (ET) = 188, Brew Temp (BT) = 187.
T=20s. ET=191, BT=202
T=30s. ET=191, BT=202.
T=40s. ET=191, BT=203.
T=50s. ET=192, BT=202

The BT kept declining from here on out, but in almost all cases I would have pulled the cup by now, so for our purposes this is a quickly rising, then flat, profile.

What happens if I leave the boiler pressure/temperature lower by leaving the switch at minimo, and doing a few half-pumps to get the group up to temp? I got a pretty stable preinfusion temperature in mid 180s, and then when I started to pull the shot the temperature swung up to 203, then 204, then back to 203, then down to 201 after 40 seconds of pulling. So depending on how slow of a pull I would be using, this would either be a rising/flat, or a humped, profile.

Finally, I tried to rig the game in favor of a declining profile by pulling with the hottest boiler and the coolest group I could manage simultaneously. I started cold, waited for the boiler to start venting, and then pulled the shot with the ET measuring 152(!). I would never do this in normal use, but I was curious. This time I got a very similar brew temperature curve as in the previous examples, except that the whole shot stayed cooler after preinfusion. T10=179 (that was when I started to pull), T20=185, T30=186, T40=187, T50=184.

So, to my great surprise, my data seem to show that even the brass sleeve machines tend towards either rising-then-flat profiles (with short-to-medium duration shots) or slightly humped profiles (for slower pulls). If anyone has any requests for follow up testing, now that I've got the rudiments worked out, let me know.

Any and all testing you do will be read and appreciated. Did you pull these all at the same psi and what psi were they pulled?

You are measuring (like Matt Hoffman) the brew temperature with a probe just below the the shower screen. Does it deliver a temperature during pre-infusion? That would be interesting to know.

Mark,

Great report. Thank you! Now I know what's happening in my brass sleeved Europiccola. Since you offered, I would love to see the graphs, even if they're not the best resolution.

day wrote:Any and all testing you do will be read and appreciated. Did you pull these all at the same psi and what psi were they pulled?

I do not know the PSI because the Caferina has no manometer (and no sight-glass on which to install the standard Pavoni version of one). I could probably jury rig something on the steam-wand if people are really curious. My guess, based on using a second-gen machine with a similar OPV system, would be in the neighborhood of 0.7-0.8 bar, for what little that is worth.

Chert wrote:You are measuring (like Matt Hoffman) the brew temperature with a probe just below the the shower screen. Does it deliver a temperature during pre-infusion? That would be interesting to know.

Yes, the standard pre-infusion temperatures were around 185-190F in my tests.

drgary wrote:Mark,

Great report. Thank you! Now I know what's happening in my brass sleeved Europiccola. Since you offered, I would love to see the graphs, even if they're not the best resolution.

Sure, here are some of them. Brew temperature is in green, group exterior temp is in red.

The first one is a long, boiler-pressure preinfusion, followed by a fast ramp up to full pressure:



The second is from a shorter preinfusion followed by a more gradual ramp up to pressure:

Interesting, but it seems to me you are missing the most relevant measurements, the boiler temp (or pressure) and the decline in brew temperature from time 0-10. I imagine most of the action (delta temp) occurs when the temperature differential between the boiler water and the group metal is greatest.

The relevant question to me is:

How can one gain accurate and precise control over brew temperature with a home lever? This depends on the boiler temp, the group temp, and time. The taste of the resulting espresso will depend far more upon this than it does upon a 1-2 degree hump or dip in brew temp over a 30 sec pull.

My 2 kronors...
PC

I did a lot of testing today. My first two pulls were in the 85-86 degree C (group) and the water on the puck was 92-93 and 95-98 at 9-10 psi. My third started at 102 dropped to 95 and went back to 101. After that it didnt matter what I did. I dropped the group to 65 with a nice bath, i lowered psi to 5...shot after switching off...even waited like 15 minutes... Prein fusion was still at 102 and wouldn't come down, even though I had bar and group so low. I think the connecting tube between the group and the boiler, and the top of the group, get so hot that without directly cooling them with some method (will test with towels wrapped in ice for now but have some ideas coming together) that it is impossible to pull a shot properly for quite some time, and that initial appearances may be deceptive without getting readings at the puck.

Are you getting similar results? And please post psi as it means much less wo knowing the temp of incoming water

RIght. Herein lies the problem of pressurized home levers. The only temperature measurement that counts is brew temperature, and the problem lies in how to cool it effectively.

In theory, longer dwell time in the group (i.e. preinfusion time) will cool the water further because there will always be a temp differential between group and boiler water. As the group heats and it's capacity to sink heat to the outside environment diminishes, dwell time will need to increase to compensate.

In my short time with the Pavoni I noted that the group sank heat more slowly than does my Ponte Vecchio group. I attributed this to differences in surface area:volume ratio, but I'm just guessing there. Anyway, those heat sink devices used on some Pavonis ought to increase the rate of heat transfer.