jdavidwaldman wrote:So we just got a Scace 2 and I am using it to try and understand our Synessos. If this has been exhaused elsewhere, please re-direct me. (We also have one of the first WBC Competition Aurelias, but, unfortunately, not enough electricity to run them side by side.)
I read the thread concerning pressure and think I understand - interestingly, our machine gauges in at 100-101 PSI while the machine gauge says 9-point-something (125 or so psi). We adjust to taste, so, no big deal. I'll leave pump where it is.
The pressure values that you observe make sense. You should see lower pressure at the group since there is significant restriction to flow along the path from internal gauge to the group. Your observation that taste is the most important criteria is correct. The measurement results give you the ability to quickly return to machine to the optimum settings if something changes down the road.
[quote="jDifferent story regarding temp - it ramps from 198 (the PID setting for brew group in question) to 206-207 by the "end of the shot" (say 25 seconds). Within initial 6-7 seconds, we are at 202-203. What are you finding with other machines, whether HX or PID? I'll give Mark a call, but curious what you have discovered in your cafes/labs/roasteries. Is this broad temp swing abberational or "acceptable" for a PID? I am confused. I thought well-designed PID meant what you dial in is what you get, or, is the temp, in fact, elevated due to pressure? - which begs the question, in light of recent pressure profiling experiments, is the pressure the only way to really keep the temp where you want it? (So, what's the true benefit of PID in this context?) Is the Scace 2 accurate for Synesso architecture?[/quote]
WRT the 198 degree setting - I'm guessing that Mark programs an offset into the PID controller. In the real world there's no way in hell that you can gain temperature on the way to the group unless you add heat to the water somehow (remember that temperature is a measure of heat in a substance). There are, however, parts that cool off if the machine is idle for any significant length of time. For LM, this is mainly the lower surfaces of the group that are not "wetted" and the dispersion screen. I'm guessing it's similar for Synesso. So those parts need to be heated up if the machine has been idle.
WRT the difference between coffee and the plastic insert of Scace devices - This is a pretty complicated issue. The temperature probe measures the local temperature of water as it hits the probe. If the water flow past the probe is sufficiently quick, and the distance between relatively cool surfaces and the probe is sufficiently large, then there will be no affect on the probe due to relatively cool surfaces. In the Scace, the distance between the probe and the internal surfaces is larger than would be the case if one were to lay a thermocouple on top of a bed of cool coffee. So temperature measured by the Scace should more accurately reflect what is actually coming out of the group. On the other hand, the filter basket and portafilter of the Scace will pull heat out of the group if they are cold. Presumably you keep your portafilters in the group so that they stay hot. you should similarly warm up the portafilter of the Scace.
Coffee has thermal conductivity approximately equivalent to wood and most plastics. So its ability to absorb heat is similar. On the other hand, there is waaaaay more surface area exposed to water in a packed coffee cake than there is in a Scace. So the coffee can absorb heat much more quickly than the insert in a Scace. In the Scace, the surface of the insert heats pretty quickly. Then the heat migrates a long way through the material, so the Scace insert heats up much more slowly. Again, this shouldn't be a problem since we're really interested in the temperature as it hits the coffee cake.
You might ask why we're only interested in temperature at this point, and my answer is because things get waaaaay more complicated if you want to begin discussing temperature buried inside the cake. Coffee at the top of the cake and in the center heats up much more quickly than coffee at the bottom and on the sides. Eventually the temperature profile in the cake reaches some sort of equilibrium. So there is a time-dependent, and position-dependent component to brewing temperature profiles inside the cake. That shouldn't really bother us too much if we're consistent in our preparation. Given that we are consistent in our dose and tamp, we should get the same temperature profile every time in the cake if the upstream temperature (the one reported by the Scace) is the same every time. This assumption is valid because the thermal properties of water are invarient - they're a fundamental property of water.
If you're not doing so, I'd suggest that you heat up the Scace by leaving it in the group for 10 minutes of so before you start doing any serious measurements. Then use the Scace exactly as you would pull shots. Pull it out for 10 seconds or so immediately before pulling a simulated shot. Flush the group exactly as you would when making coffee. Pull your simulated shots for the same time as you shoot for when your grinder is adjusted correctly. Pull sets of simulated shots at a frequency that is reasonable in your shop - prolly 1 extraction per minute is a practical max frequency.
With regard to the increasing temperature - The temperature is increasing because something in the flow path is absorbing heat. It's either the portafilter surrounding the Scace, or something exposed within the machine. The exposed plumbing on Linea AVs is particularly bad in this regard. You should run simulated shots at 1 shot per minute to see how the machine behaves when its running at full chat.
[quote="jDo we want the temp to stay the same throughout the entire extraction? Is this an advantage of the HX? SO confused. Thx.[/quote]
Well that's a million dollar question, and there are plenty of folks who will tell you with great certainty what the answer is. For example, i'll tell you with great certainty that the current limitations of espresso machine design make it pretty damn hard to answer this question in a way that will stand up to rigorous peer scrutiny. The current state of the art wrt reproducibility relies on massive groups that are actively heated by electric heaters, thermosyphons, so-called "saturated groups". The engineers who designed these group get good reproducibility by striving to maintain constant temperature, so the temp profiles that they produce are flat. As soon as you try to add heat to, or remove heat from the water during the extraction (increasing or decreasing water temperature), you change the temperature of the surrounding metal, and then the apple cart gets tilted because things ain't in equilibrium no mo. It's really tough to maintain reproducibility now, so any presumed advantage in taste gets confounded by the machine's inability to produce the same temperature distribution every time.
With less certainty, but with lots of conviction, I'll tell you that if you pose that question to an engineer whose business is designing espresso machines, the answer you get will be dependent on whether the engineer designs double boiler or hx machines.