Mark Prince did some testing with the Breville Double Boiler and found that it had this much temperature stability. The Breville PID is incredibly accurate. Kind of strange to think that a $1200 machine has better temperature stability than some DB machines which sell for double that price. Here's his post: Click Here (plus.google.com)
In all honesty, I don't think that 1 F temperature accuracy is that important. 1 C temperature accuracy is more reasonable. Maybe I'm a little ignorant, but do you really think that you could tell the difference between a shot which was brewed at 203 F as opposed to 200 F?
2) Temperature profiling. I certainly want to control how much the temperature drops while brewing. Being able to control the shape of the temp vs time curve is even better.
Every machine is designed with a repeatable, consistent temperature profile. A DB will deliver water differently than a HX will. Larger heat exchangers behave differently than small heat exchangers. I think what you are asking for is kind of like a car with 500 Horsepower that gets 50 miles to the gallon. It just simply isn't possible.
Now, I do recall reading some threads on HB about people experimenting with lever machines and using ice packed around the grouphead to deliberately drop the brew temperature while the shot was being brewed, but not only was this a bit of a hack, doing this won't always lead to a better shot. In fact, it could make it worse.
There should be some measure of reasonable temperature consistency across the shot so that the machine produces the same temperature drop every time as a baseline.
The only way I could see building a machine which could drop the brew temperature over the course of the shot would be to put in a water chiller and modulate its output to cool down the brew temperature on demand. I don't honestly see that being very practical at all.
3) Pre-infusion/slow pressure ramp up. It provides more consistent good taste for me.
Vibration pump machines already do this to some degree, but it's not very controllable. The La Spaziale Dream has controllable pressure profiling. It's one of the cheapest machines on the market which has this capability. Otherwise, you would be looking at purchasing a machine with a manual saturated group, like the La Marzocco GS/3. These machines allow someone to completely manually control how much pressure is applied to the puck in an infinite manner. Think of a dimmer switch for pressure. It seems to me that the GS/3 is the "Entry Level" for these types of machines. After that, you are now in "new car" price territory.
I don't know about you, but IMHO spending as much on an espresso machine as a brand new stripped down Hyundai Accent seems a bit nuts to me. (I'd like to apologize in advance to anyone reading this who actually owns a Synesso or a Speedster.)
4) Flow profiling. I want a specified extraction ratio and time - x grams of coffee in y seconds. Without having to throw away a few shots to adjust the grind to get there.
You know, I'm not sure if you are being serious with this one. Imagine a portafilter with a small hole on the bottom of it with an adjustable aperture. That's how you would regulate flow. In saying that, I just described a pressurized portafilter.
The whole point of making espresso is to control flow by adjusting dosage and grind of the puck. By changing the thickness and consistency of the puck, you regulate the water flow through it and force the water to brew all of the right aspects of the puck. As soon as you take that away, you're not making espresso anymore.
Garbage In, Garbage Out, for every step of the process. From Beans to grinder, grounds to machine, coffee to cup.
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