drgary wrote:If you lock a portafilter filled with coffee into the group, the initial steam would release through the coffee cake and some of it would be cooled by the room temperature coffee particles. The coffee swells with water creating resistance so the flow of boiler water almost stops. Water that has been released into the group now heats the metal parts and the group acts as a heat sink, cooling the water to proper brew temperature. Coffee brewed this way tastes as it should.

That's essentially what I concluded in Ponte Vecchio Lusso brew temperature tests and added:

HB wrote: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.

I believe the difference in "brew experience" is especially noteworthy in dipper type lever espresso machines because they rely significantly on the grouphead to temper the water temperature. The Scace thermofilter flow rate is nice and even from the get-go because its "puck" doesn't have to absorb water, which reduces the time the grouphead has to exert its influence.

The Lusso's peak temperature with a thermofilter was around 207°F; I assume it didn't peak as high as depicted in your video because the Lusso's shot volume is so teenie tiny.

erics wrote:The adjustable check/relief valve prevents any flow through the thermofilter until a particular pressure is reached. I also used a smaller orifice to more closely replicate the lever flow.

I hold a folded cloth against the Scace outlet to prevent flow until the lever is lifted. Wearing an oven mitt is advised if you use this method. Ran a number of Scace tests when I first received my Bosco. The Bosco is a hybrid dipper. The group is mounted to the frame with a large tube feeding boiler water into a custom reservoir behind the group. Your shot water is pulled from the reservoir, not directly from the boiler.

Testing was done with a P'stat setting of 1.25 bar & a 2 hour machine warm up. With no initial warm up flush the shot water temp peaked between 196°-198°F & dropped rapidly into the low 190's by shots end. I only saw that large temp drop off (low 190's) before the first shot/flush of the day. After that if the group was idle for several hours & I didn't flush I'd see a peak temp in the 198°F range but a normal 3°-4°F temp drop during the shot. With a 3 second flush before you start grinding & shot prep the shot water temp peaked at 201° & slowly dropped off 3°-4°F during the shot. Pulling 4 simulated shots in a row with one every 2 minutes no flush was necessary after the initial one & the water temp peaked approximately .75°F higher with each shot with a similar 3°-4°F drop off by shots end.


Could be just the blends/Single Origins that I've used but so far I find that my best tasting shots are with the 201°F starting temp.

I wonder what the temperature is when using a naked probe attached to a fast thermocouple on top or in a puck of actual coffee. When I did this, I got about 201F on my strega without flushing.

Thanks, Gary, for sharing this information, which seems to be yet more confirmation that lever groups are complex systems that cannot be easily understood using pump-machine-derived assumptions or tools. I think the thermocouple-in-filled-basket technique remains the gold standard for understanding the effective temperature profile that these machines produce, and such tests have repeatedly confirmed what anyone's taste can show, which is that a properly managed lever group will not yield a burned-tasting cup.

Very interesting!

Here is what it looks like on a Faema Lambro (Zodiaco group, thermosyphon):



Here is a summary of the study:

"With this routine I let the group coast at 178F, insert a room temperature portafilter in, prepare the basket, insert a bottomless portafilter with the basket, do a 15 sec preinfusion (I know it is long preinfusion, but I need a longer preinfusion with the lower boiler pressure), preinfusion starts at 199 - 200F, raise the lever, extraction starts at 199 - 198 and goes down to 193F. At this point the group temperature is at 178 - 179F. Without any delay I can insert a room temperature portafilter and pull another shot in 2 minutes, enough time to dump a spent puck, wipe the screen and the basket, grind some coffee and prepare a new basket. I can do back to back shots all day long with basically no shot to shot difference (1F - 2F max).

So if I want a cooler sub-200F shot, and I am pulling a shot after machine has been idling, I walk up to the machine, insert a room temperature portafiler, prepare the basket, pull the shot. If I want a hotter, 200F - 201F shot, I don't insert a room temperature portafilter and pull the shot."

Here is a full thread: Faema Lambro Brew Temperature.

rpavlis wrote:We must further remember that we really are chromotographing coffee components when we make espresso.

Yes, of course!

JohnB. wrote:I hold a folded cloth against the Scace outlet to prevent flow until the lever is lifted.

You can also manually restrict the handle on a spring lever to produce the appropriate flow rate if it's too fast.

You can't restrict anything without an opposing resistance to flow, e.g. a coffee bed or needle valve restrictor. John's talking about filling the group and empty basket with water only.

TomC wrote:You can't restrict anything without an opposing resistance to flow, e.g. a coffee bed or needle valve restrictor. John's talking about filling the group and empty basket with water only.

If you restrict the handle movement, you lower the piston pressure from the spring, which reduces the flow rate through the Scace outlet. On some spring levers the unrestricted flow rate is much higher than the WBC protocol specifications for group temperature measurement.

Bob_McBob wrote:If you restrict the handle movement, you lower the piston pressure from the spring, which reduces the flow rate through the Scace outlet. On some spring levers the unrestricted flow rate is much higher than the SCAA protocol specifications for group temperature measurement.

Yes, but if you're after accurate temps in the basket, it doesn't serve any purpose to have the pre-infusion gush immediately thru the group and into the basket. That's my only point. What you're describing above will give you more reliable tail-off temps likely, but the initial gush of water will exceed the desired flow. Whatever you see on the Scace will not correlate to what's happening when instead there's coffee in there slowing down the flow of water from beginning till the end. The spring is not involved until the extraction (or a group that's filled with water). I'm only talking about the pre-infusion flush of water.