The guys at Slayer did a little piece on the Vita BOSCO.
http://www.slayerespresso.com/2008/05/12/caffe-vita-leveraging-the-bosco/#more-132
Some interesting points made, particularly about lever machines, HX boilers, and temp stability. Sounds like the ideal lever machine would be double boiler or open boiler with no steam capability.
I'd like to see one with saturated groups too. Temp stability is such a critical issue that you'd think someone would design a machine around that, not some esoteric feature that has little impact on the quality of the coffee in the cup?
Commercial levers have more (or as little depending how you want to look at it) thermal stability through metal mass than an old e61. I would say the average group off of one of my commercial levers weighs just over 25 lbs (I just established that with a disassembled group in one hand and a 25 lb weight in the other), with the average e61 weighing in around 10 lbs. That is a lot more metal. You need to hook up one of your PIDs to a lever !
I agree that the thermal mass of those huge groups is impressive - I thought the Rancilio/CME lever group was going to cause a hernia. But I'm not convinced that thermal mass and temp stability are the same thing. That 25 pound hunk of metal is just as easily stabilized at too high or too low a temperature, rather than the ideal brew temp. If it has a thermal siphon connected to the HX it'll be too hot if it sits idle. If it's just hung from the boiler, it'll be too cool as the heat is wicked away into the atmosphere.
Ideally, the group is the same temp as the brew water and no heating or cooling flushes are necessary. That's not the reality I've witnessed in lever machines, except in a commercial environment where the machine is in continuous use. That's why I'd like to see a fully saturated group fed by the brew boiler, not the HX.
