well just to dredge up an old thread. It seems that you can separate the espresso journey into steps (excluding steam toys).
Step 1 - Single boiler dual use systems. I suppose one should look for units that can be upgraded to step 2 use. The most famous entries at this level would be the Gaggia Classic/Baby series and the Rancilio Silvia. They have good internals and record of durability. The 3 way solenoid is a nicity that most seem to value. There are other entries that can be found for a good price - Isomac Venus/Maverick/Giada Le'Lit PL041, . Skill is needed to get extraction at the proper temp. Usually requiring temp surfing.
Step 2 - This is the reason to be somewhat careful about the machine one purchases as a step 1 unit. If you are somewhat mechanical (or know someone who is), you can upgrade some of the SBDU's with a PID to get a more consistent brew temp. Some people buy SBDU's with the intent of adding a PID right away and some buy units already PID'd. I get the impression that you want a unit with pretty good innards to make it worthy of the additional investment of time and $$. Some people can be quite happy for a long time with this kind of unit. We will have to see how long B/Java stays here after his latest round of upgrade-itis.
BTW, I am surprized that B/Java (Mr happy-with-stock-Silvia) was able to go through this little episode of upgrading with little fanfare and less humor at his expense. B/upgrader got off easy this time around.
Step 3 - Heat exchanger seems to be the next step (cost wise at least). The motivator for moving to this step is "need for steam". People seem to get frustrated when trying to make a bunch of milk drinks in a row and want the instant steam provided by an HX machine. Temp surfing as done with this machine seems a lot easier and consistent than on a SBDU unit.
Step 4 - Double boiler units with separate boilers for steam and brewing seem to give the ultimate control over steam and brew temps. For most this is at a much higher $$.
then there are lever machines that really don't fit the progression.
Do I have it right?
I agree with what you said, but would clarify it a
bit more. Any espresso machine that is properly tuned has the capability of making good espresso. What is properly tuned? Control of the brewing temperature in 1°F increments, and control of brewing pressure at or near 9 bar pressure.
With the above in mind, I'd rate the necessity of an adjustable OPV & PID as being far more important than a 3-way valve, which contributes nothing to the quality of the shot. There are other factors: boiler size & material, heating element power, group design, ..., that contribute to the quality of the machine; but these are far less important than the ability to tune the brew temp & brew pressure.
