At the time I didn't elaborate on my assumption that "fast pressurization means poor preinfusion", but thanks to Sean Lennon, I'm able to present some interesting data for your consideration. First a little background...Plainly stated, dialing in the temperature and extraction was too darn easy. In retrospect, I realize that I carried an unstated assumption into the evaluation: Fast pressurization means poor preinfusion (wrong!). This bias originates in my experience with vibration pump E61-type machines, which pressurize much slower than a rotary pump's blink-of-an-eye 2-3 seconds.
Yesterday morning the doorbell rang. When I opened the door, there was a large black pelican case with triple seals sitting on my porch, looking decidely serious. It was nice and sunny. I thought, "Hmm-m, what is this?" Sean had e-mailed me the day before telling me to expect a package. He didn't tell me what to expect. Whoa, an espresso machine Mr. Wizard tester kit! I'll leave the specific hardware description to Sean, the important thing is that with this gear, you can create combined pressure and temperature profiles with data points captured easily at 20 per second. That adds another dimension to an analysis, plus the capture rate is a lot better than my own setup plugging along at one data point per second.
Lino stopped by this afternoon to help me answer one question that puzzled me for months: The Elektra A3 appears to ramp up in pressure in seconds, so why isn't it "unforgiving"? Was there something different about its pressure increase? Was there an interval that should be rightly called preinfusion, however brief it might be? We took a stock thermofilter and tee'd in a transducer (translates pressure into an electrical signal). Now we could record the ramp up in pressure. Of course, it's not the same as a real coffee puck since dry coffee would act as a cushion, but it does give us a means of roughly comparing the machines' initial pressure characteristics.
Guess which one is the A3:
Comparisons of the pressure profile of three espresso machines (temperature omitted for clarity)
Keep in mind that these measurements are taken with a portafilter that's already full, so the ramp up is more rapid than normal (each vertical gridline is one second, each horizontal gridline is 10 PSI). Nonetheless, the A3's profile in the middle stands out as starkly different from the other two - the pressure rockets up in barely one second, which is consistent with the rapid onset of its extraction in actual use.
What I learned from this experiment is that pressure ramp up may contribute to the "forgiveness factor" we attribute to the E61, but clearly it isn't the whole story. Care to guess what the other two machines were? Or offer what you think might be other key contributors to the forgiveness factor?