Scace 2 & Synesso

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Scace 2 & Synesso

Postby jdavidwaldman on Mon Aug 17, 2009 2:26 pm

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.

Different 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?

Do we want the temp to stay the same throughout the entire extraction? Is this an advantage of the HX? SO confused. Thx.
... but how does it taste?
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Re: Scace 2 & Synesso

Postby Robert Goble on Mon Aug 17, 2009 3:34 pm

Talk to Mark David, but several things are going on,,,

Coffee acts as a heat sink, absorbing thermal energy throughout the duration of your shot. Mark calibrates the temps and tunes the machines at the factory to perform with coffee in the portafilter so that there is temperature stability through the shot with coffee.

The Scace 2 has different thermal absorption properties than coffee in a pf.

Using a scace requires a real understanding of what you are trying to measure. You have to develop a measuring protocol that you follow religiously (eliminating variable that affect data).

You can then take relative measures.... at points within the protocol and use that as your reference data.

You can then apply that data -- but you have to be sure what and why you are measuring for it to be of any use.

R.
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Re: Scace 2 & Synesso

Postby nick on Mon Aug 17, 2009 6:16 pm

Coffee is hydrophilic. It wants the water. Not as true with the space in the Scace. I actually have a theory that once the Scace gets going, there is (or are-plural) air bubble(s) trapped in the upper area, sometimes leading to bad readings.

Here's what I do (credit to B-LUD from CCC): hold the Thermofilter under the group, use the group to fill the Scace 'basket' with water, and while the pump is on, insert the portafilter. You'll get a higher-than-normal reading, but it might make more sense vis-a-vis the temp ramp-up and such. It's just an idea, and needs further testing, but try it out and see what you think.
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Re: Scace 2 & Synesso

Postby gscace on Wed Aug 26, 2009 7:27 am

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.

-Greg
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Re: Scace 2 & Synesso

Postby naznar on Thu Sep 03, 2009 9:40 am

The brew group stability of the Synesso is totally dependent upon both the setting of the brew group and the setting of the steamtank. The Synesso was designed to run at a steamtank pressure below 1.4 bar, holding brew group stability above 200F. Many around Portland have their steamtank pressure set higher, which increases the temperature of the prefeed brewgroup water. At a steampressure of 1.8 bars I feel pretty confident one cannot hold stable brew water below 201F, without restricting the flow through the heatexchanger tubing.

Using the Scace device to me requires measuring spaced on-off intervals to simulate a busy and slow bar, over a longish period of time. Synesso's calibration is usually 2F off from the Scace device, so Synesso tells me. I believe the Scace measures 2F hotter than if you were to use grounds and a drilled out basket w/bead probe to calibrate.

At the shops serving my coffee we are trying to stay super stable at 198F, so we have restricted the prefeed lines running through the boiler, and then had to recalibrate the PID offsets.
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Re: Scace 2 & Synesso

Postby James Hoffmann on Thu Sep 03, 2009 10:39 am

Why would anyone want to set their pressure that high? I can't imagine people need more steam than 1.4 bars?
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Re: Scace 2 & Synesso

Postby Robert Goble on Thu Sep 03, 2009 11:30 am

Hey Naznar

You are right in that the Synesso is tuned (ie - engineered) for the diameter and length of the HX tubes to provide temperature stability at certain atmospheres (ie, elevation) working with certain temperatures and pressures (water volumes). And that this can be "tuned" by using teflon inserts to both restrict the HX tube diameter but also insulate it from heat transfer so that it doesn't arrive too hot in the brew boiler. Usually this tuning is only required at high elevations or extreme conditions.

As Greg has pointed out --- there are lots of variables at play that you have to understand in order to create a proper and useful scace protocol for your equipment.

As for Portland's alleged high steam pressure --- I heard that they can steam milk for a single macchiato in .243 seconds...
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Re: Scace 2 & Synesso

Postby naznar on Thu Sep 03, 2009 2:46 pm

From what I understand the Synesso was designed around brew temperatures over 200F. The diameter and length of the stock heat-exchanger tubes were based around this. If you want to keep super stable below 200F either you drop the steamtank pressure/temperature, or reduce the area inside the heatexchanger (by slipping teflon tubes inside the SS heatexchanger tubes.).

Robert- I believe the certain temperatures that the Synesso was designed for to be about 201F or higher. So basically if you want to go lower without sacrificing steampower the best option is to de-tune the heatexchanger, and then re-calibrate the PID offsets.

One of the reasons for the 1.8bar pressure is perhaps some folk switching from stock Synesso steam tips to the small hole high pressure low volume tips, which steam much slower. So in order to increase the speed of milk steaming steamtanks were turned up, this of course adds to the problem of stability at lower temperatures.
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