It has always seemed to me that knowing the temperature of espresso as it emerges from the machine is a really important thing. After a search this morning I found a piece of brass bar stock that measured about 25mm in diameter. I cut it to what seemed the best length, and bored it out and tapped 3/8" BSPT through the cylinder. I turned down the one end to make a spout, and then I bored a 4mm hole at an angle to receive a thermometer.



I deliberately cut the 4mm hole at a slight upward angle to prevent the thermometer probe from falling out and to prevent espresso from coming out along side the probe, though I made it a precision fit.

As soon as I finished it, I tested it! The thermometer read 94 degrees toward the end of the shot.

(If anyone else make a thermometer well like this, remember to be sure to put the hole for the thermometer in such a place that it is on the RIGHT side of the machine, because of the left handed La Pavoni portafilter.)

rpavlis wrote: I deliberately cut the 4mm hole at a slight upward angle to prevent the thermometer probe from falling out and to prevent espresso from coming out along side the probe, though I made it a precision fit.

Hi Robert,

I'm planning to make some measures for a premill La Pavoni as well. I use 1mm probes though. Is your probe sensitiv/quick enough?

You wrote 94C at the end of the shot. What was themp at the start or in the middle pls?

Gabor

One would be better off with a slightly faster probe than the one I use. This one has a stainless steel cover, and stainless is a poor conductor relative to most metals. It takes it about three seconds to get within a degree of the final temperature when placed in water 40 degrees above ambient.

I have left the probe in the machine from turn on. The heat conductivity to the probe point below the portafilter is slow when all the heat coming to it is by conduction through the group and portafilter. It rises from about 24 to 26 by the time the pressurestat turns off. After the steam wand and group bleed it shoots up to about 50, and then it quickly falls back to about 40. During the next 3.5 minutes while I am waiting for the group to get up to temperature it rises to about 54 degrees. I always make the first shot by putting the basket into the portafilter, raising the handle to release a bit of water, lower slightly, and then put the portafilter in place, and then pull the shot immediately. I pull the lever until only about 2 or 3 grams of espresso emerges. The temperature stabilises at about 50-60 while I raise the lever fully again. As the shot begins the temperature stays around 60 for several mL as the coffee and filter basket are soaking up the heat from the water. Then after perhaps 10 or 15 grams the temperature soars quickly to a bit over 85, because of thermal lag it has to be even faster than it appears. Then the temperature tends to rise slowly, and by 30 grams or so it gets to about 93. Immediately on finish the shot without the espresso running over the probe the temperature falls.

With a second shot the temperature profile is similar if I simply put the loaded portafilter on the machine and raise the handle then. It gets too hot if I use the technique I use for the first shot.

With a more makeshift system, I learned that a ten second dip in a ramekin of room temperature makes subsequent shots similar to these too. (One needs to pull the handle half way up to get enough cooling doing this.)

Smaller probes would provide less thermal lag. I have one from a microscope heated stage I built, but it has only a glass tip, and wire leads would short out if I used it.

rpavlis wrote:It has always seemed to me that knowing the temperature of espresso as it emerges from the machine is a really important thing.

Robert,

This question is more from curiosity than skepticism, because I know you think about these things carefully. What do you think that will tell you to improve your shot-making?

The important thing is that measuring the temperature of the shot's temperature while it is being made lets you know exactly how well the measures taken to control temperature have worked in a rather quantitative way. This information can be used in subsequent shots. Flavour is not a good guide because different coffees taste very different. Temperature measurement with thermometer wells is the standard way to set up laboratory instruments that need thermal check points. The arguements for using them here are at least as strong as thy are in instruments.

I should try to talk the University laboratory manager into saving a broken 100 mL graduated cylinder for me when students break one instead of discarding it. I could saw it off to the right length and measure volume accurately. I have never seen a kitchen measuring device that is worth messing with because of poor precision. Then I could make a graph of eluted volume vs. temperature.

It also turns out that one can use the initial portafilter temperature to correlate to the final temperature. It would be better if I could find a faster responding temperature measuring device than the one I have been using, though its response is fast enough to be very useable.

You could coat the individual leads of the thermal bead you have with lacquer (fingernail polish) and that would insulate them to allow use in the effluent stream.

I have been using the spout thermometer well now for a week. It really does help the procedure to watch the temperature of the espresso as it emerges from the machine. During any pull there is a sudden point where the temperature jumps above 90 degrees. To me the best espresso seems to result when the final temperature is very close to 93 degrees.

On the 1974-2000 group models at least, if one put the portafilter on the group during the air bleed, and leave it there afterward, one can watch the temperature of the group rise as heat diffuses through the group and down to the portafilter. I have found by making at least 15 cups this way that when the portafilter reaches the temperature of 53 degrees, I must immediately remove it, put the tamped coffee in the filter basket into it, raise the handle until a bit of steam is emitted, lower it until it stops, and then install the portafilter, and fill and then pull the shot. Every time I did this for the first cup, the final temperature was always between 93 and 94!!!!! This seems the way to get the perfect first cup!

The perfect second cup seems to result from pulling it within five minutes, with no further temperature measurements.

I have not found a convenient way to use this for later cups, but I seldom make more than two at a time, so I have not worried about this much yet. I do know, however, that a ten second ramekin of cold water drawn into the group before each shot after the second seems to result in close to the 93 or so, from just a couple of tests.

Since this thing seems so great to me, I am attaching a second image of it, this one close up.

I've been taking temperature readings with an infared thermometer on my LP Pro just to see what is going on. It's interesting to see what readings I get when moving the laser from boiler through the group and down to the PF. The top of the grouphead seems to be the hottest with the temp dropping 30* by the time I get to the bottom.

Dear Rpavlis,
Your efforts in this regard are greatly appreciated. You have been a source of valuable information to me and, I can read, to many others who are on the La Pavoni learning curve.
I, too just finished a project to record the temperature coming out of the PF. Since you tinker way better than I do, it had to be sewed on with stainless steel filament wire. Not to hijack your post, so it is posted in the 'Espresso Machines' section of this forum under the heading A Poor Man's Scace Device. It was originally intended for the La Pavoni, but I am adjusting the pstat of a Londinium and I am interested in the results of that, first.

Not to be a PIA but drgarys question is mine also. The major mod that drastically shortened my learning curve for finally getting consistently good shots out of the La Pavoni was knowing the boiler and group temperatures to a better and more responsive degree that a pressure gauge and OE temperature strip could tell me. I put one thermocouple on the group bell andanother on the boiler at the height that the downtube draws water:


These show me the target temperatures that prompt me to pull the shot. By comparison, the PF measurement will only tell me what I accomplished after I committed to it. The PF value is not useless. For an experienced used such as yourself, it may allow fine-tuning of technique. For a beginner, however, it is more important to be able to know when to pull the trigger, and I find the 'bell and boiler' readouts more useful to learn from.
Parenthetically, you can see that the Europiccola has a pressure gauge on the top of the sight glass and you can just see the edge of the OE temperature strip on the front of the group profile photo. I am noting the coarser behavior of the gauge and temperature strip and hope to be able to use these alone after I take the TC probes off - like training wheels.
Buckley