akallio wrote:Because there is some offset between boiler temperature and brew temperature, brew boilers can go above 100 C. However I am not sure what happens when brewing starts. Opening the passage from boiler to the group should release the pressure and drop temperature to 100 C, but on the other hand pump starts to push in new water and the system is quickly pressurised again. I guess there is more than 100 C in the boiler when brewing, because machines with several degrees of offset are still capable of producing boiling brew water. Non-pressurized kettle would thus limit the maximum brew temperature, but not necessarily too much. Or I might be completely wrong here...

Another issue is that the pump should be capable of handling boiling water, because pressure needs to be created after the kettle. And there needs to be another pump for filling the kettle. Maybe having a pressurised boiler is not that bad after all?

But I had suggested an unpressurized kettle, not a boiler under pressure, for the brew water, with temperature set precisely for desired brew temperature. The thermoblock would only have to raise the temperature from brew temperature to vapor, not from room temperature or colder mains temperature.

You don't need boiling water to produce espresso. The pump would create the brew pressure. As for filling the kettle, that could be done under mains pressure.

But I had suggested an unpressurized kettle, not a boiler under pressure, for the brew water, with temperature set precisely for desired brew temperature.

That would dictate saturated group, because there is not much room for offset. Naturally saturated group is not a bad thing, but quite the opposite.

The thermoblock would only have to raise the temperature from brew temperature to vapor, not from room temperature or colder mains temperature.

I guess this is the big question: can a thermoblock produce lots of dry steam from (preheated) water? If not, then a boiler is needed in any case. Typical thermoblocks sure can not, but it seems that no one really knows if building such a thermoblock would be feasible in principle? At least in theory it should be?

Steam thermoblock would require a dedicated pump (assuming simultanous use), but that's not a biggie of course.

You don't need boiling water to produce espresso.

If the temperature offset between the group and the heat source is more than, say, 5 degrees, then you do.

The pump would create the brew pressure. As for filling the kettle, that could be done under mains pressure.

Yep, in commercial setting there's no problems here. Making a tanked prosumer version would be a bit difficult: kettle needs to integrated into group and tank would need to be placed above it for gravity feed. It would make the machine very tall. Or space under the group very small.

This idea about a boilerless machine is intriguing. However I am not sure that a machine with a kettle, a thermoblock and 2 pumps is more straightforward than one with a boiler and a pump.

akallio wrote:That would dictate saturated group, because there is not much room for offset. Naturally saturated group is not a bad thing, but quite the opposite.

Almost every gravity fed lever has a saturated group. The Brunella has, the MiniGaggia has and also the Zerowatt. The Peppina doesn't, but the offset is 1 degree and the Caravel has a semisaturated group. No problems there.

Yep, in commercial setting there's no problems here. Making a tanked prosumer version would be a bit difficult: kettle needs to integrated into group and tank would need to be placed above it for gravity feed. It would make the machine very tall. Or space under the group very small.

Don't be ridiculous. You could just fill the kettle with a jug. No reservoir necessary.

Don't be ridiculous. You could just fill the kettle with a jug. No reservoir necessary.

Good point.