gscace wrote:OK, I gotta try to nip this misconception in the bud. (snippage)
WRT 110V machines doing well enough on the tests, my Astra Gourmet can keep up at all duty cycles. It suffers from needing cooling flushes to get the temp down like any e-61 machine, but it can keep up with very short duty cycles just fine. I did some calculations on a perfectly efficient system a while ago that showed you needed 800W of heat to brew a double shot a minute, which is the fastest WBC duty cycle (10 sec wait, 15 sec dose / tamp, 25 second shot, 10 sec to knock out the puck and flush the screen). A 50% efficient machine would need 1600W heating element. The Astra's is 2kW, so you'd expect it to keep up. 1400W machines may not.
Also, the LM GS3 can keep up no problem. Not only can it keep up, the machine needs pretty much no flushing ritual at all, according to the data I have and that got posted on HB.
Ken, I disagree with your comment that the importance of temperature stabilty has not been proven. It most certainly has been studied and conclusions have been drawn that form the basis for various standards of espresso. The question is more properly "what is the stability requirement?" and that is a much harder question to answer. The opinion of pro baristas who are very highly regarded in the industry, that have tested the GS3 claim that they can taste the difference in 0.3 F changes in setpoint temperature. My own measurements put the reproducibility of the GS3 at around a half degree. Taking the square root of the sum of the squares of 0.3 and 0.5 gives you 0.6, which is prolly a good guess on what actually makes a meaningful difference. That doesn't mean that one shot brewed 0.6 degrees different is gonna suck compared to another one, it just means you can taste a difference. There are only a couple of machines out there that can produce that level of reproducibility and one of them is still a prototype. So we ain't there yet when it comes to reproducibility. With regard to temperature profile, the argument that flat line is good or bad is pretty meaningless really. It's a long way down the road before anyone's gonna develop a machine with variable profile that can test the argument, if one blindly assumes that we care about the temperature above the cake. The temperature inside the cake varies with time and position in the cake. It is most assuredly not constant during the brew cycle. The reason that we oughtta be concerned with flat line temperature above the cake is that given the technology that we use to pull this stuff off, a flat line is more likely to give you reproducible brew temps from shot to shot that can get within a factor of 2 of the minimum detectable difference temperature.
OK, I better go do some work now.
-Greg
Greg,
You are a scientist and I doubt that if you reread your last paragraph you would really conclude that XYX pro baristas claiming they can taste 0.3 degree F changes in shot temperature constitutes "proof" in any sort of scientific sense.
I read the instructions for the WBC test as carefully as I think anyone could, and the pace of shots that you describe above is different than I interpreted. For one thing, I thought shots were supposed to be measured over THIRTY seconds, which in reality means you have to run the shot for 31 or 32 data points since the first two measured temps are often the same because the brew water hasn't gotten down to the temperature sensor in the first second. I did not put two identical numbers in for the first two measurements, so I needed an extra number in order to have 30. My interpretation when you have two identical numbers for the first two seconds measured is that one hit the datalog button on the fluke a hair of a second too soon so it was not really data but junk. Also, you are counting one of the ten second intervals twice, I think. In the last 6 shots it is, simulated dump of puck/flush screen (10 seconds), 10 second wait, 15 seconds dose, followed by shot. The way I did this, which is how I read the procedure, amounted to 1 double shot plus two small "cleaning" flushes per 50 seconds, which is well beyond the rated shotmaking duty cycle of my machines. Whether they could have "kept up" with 25 second instead of 30 second or 31 or 32 second shots I don't know. Maybe I tried too hard to follow the rules as I read them.
In any event, I think being able to control brew temperature is cool and desirable. I don't know how many temperature points within the typical range (Andy says it is 196 to 204, and since he's smarter than anyone else I know, that's a range of 8 degrees F). Do we need 3 repeatable temps in this range, 5, 7, 37? I don't know. I do know that I'll have to see some blind tasting results from these pro baristas and others who claim extraordinary tasting acuity by shot temperature, before I will accept as scientific fact a need for 25 or 27 different temps in this range (one every 0.3 degrees F).
ken
p.s. I'll be offline for a few days and won't see your response until then, most probably.
