I got to thinking.... and am too lazy to pop open my Izzo Duetto IV and have a look, but even if I did that I still can't see how I won't end up with a question, so I thought I'd ask it anyway.

The original Faema I believe was a HX design. In it, the E61 group thermosyphon is powered by steam temperature water. Is this right?

If that is right, then I would expect my Izzo Duetto IV to connect the E61 thermosyphon to the steam boiler. (this is the bit I could check myself but am too lazy). If it did that, you'd have steam temp water powering the thermosyphon, which will then cool a bit through the head and when you pull boiler water through it you get stability and everyone's a winner.

BUT. If if did that, then what's the point of having a switch on the side of my Izzo to switch the steam boiler off? If you do that then the thermosyphon wont' work and you wont' be able to brew coffee, and for sure you won't be able to steam - i.e. no point being able to switch machine on this way as it won't do much.

So I'm 99% certain in a at least in my Izzo E61, the thermosyphon is connected to the brew boiler. But that is way different to the Faema/HX. I can see how powering the thermosyphon with steam temp water makes sense - it's a big old lump and it probably cools to something a lot closer than in temp than the brew boiler at equilibrium.

But how do you power the thermosyphon from the brew boiler? Then aren't you guaranteeing the brew water hitting the puck will be cooler than the temperature in the boiler because the group head powered by the thermosyphon will be cooler?

Or is it that all this is taken care of through the PID display which is actually not really telling me the true temperature inside the brew boiler which is necessarily higher to power the thermosyphon? But then you might as well only have one boiler - so that can't be it.

Either way I get to a place that doesn't make a lot of sense to me! Can someone help?

Tks in advance!

Double boiler units connect the E61 thermosiphon to the brew boiler. The boiler operates at a somewhat higher temperature than the desired brew temperature. Controllers usually have an offset adjustment to have the display show a number that is close to what the brew temperature will be, rather than the boiler.

I think you're misleading yourself a bit...

The thermosiphon loop in the E61s is a closed circuit that includes the heat exchanger, the grouphead (outside the mushroom, there's no flow down through the gicleur when the brew valve is closed) and the upper and lower pipes connecting the head to the heat exchanger.

So, when in use, in-between shots, the thermosiphon loop is using the "brewing temp" water in the heat exchanger as the lighter weight water which rises to the upper pipe and flows toward the head, heating the head and displacing the cooler, heavier water out through the lower pipe back to the heat exchanger.

Of course, in a heat exchanger machine left to idle, the heat exchanger can't help but overheat because it's suspended in the steam boiler, so yes, it is powered by the steam boiler, but in a cafe while the machine is being used to brew every minute and a half, the Heat Exchanger doesn't have many opportunities to heat to steam temp.

Thanks Both
That all makes sense. So the display is actually showing Izzo's estimate of the temp of the water that ought to be coming out of the group when brewing, rather than the boiler temp which due to the E61 lump of metal cooling needs to be higher than that, but probably not as high as the steam boiler.

Thanks again!

If you're interesting in checking or adjusting that offset setting, one way to do it without expensive equipment is described on H-B at Getting accurate shot temperature displays on PIDed double boilers without a thermometer

I've used a Vibiemme DB for fifteen years. It has no offset and displays the boiler set point when adjusting the boiler temperature and the current water temperature at the sensor otherwise. Although I prefer metric, I use Fahrenheit as the adjustment on the PID is 1° and 1°F ≈ 0.56°C, allowing finer increments.

ALL offsets are approximate as they are non-linear. By that I mean a 1° change in boiler temperature does not equal a 1° change in brew temperature. PID parameters will also affect the brew temperature. IMO, PID parameters are location specific and I have tuned mine to different values in Oregon than used in California. It's cooler, more humid and the line voltage is almost always 120 ++ whereas LA was always 118 -- and far more variable throughout the day and seasons.

Over the life* of a coffee, I might adjust temperature ±2°F depending on how it ages.

Bottom Line: Adjust by taste and fogetaboutdanumbers


*I purchase, parcel and freeze five pounds that lasts about as many weeks.

cafeIKE wrote:I've used a Vibiemme DB for fifteen years. It has no offset and displays the boiler set point when adjusting the boiler temperature and the current water temperature at the sensor otherwise. Although I prefer metric, I use Fahrenheit as the adjustment on the PID is 1° and 1°F ≈ 0.56°C, allowing finer increments.

Very interesting. I'm curious - have you done the flash boiling test in the video posted earlier in this thread to check? And what does your display temp read? How much warmer do you think your boiler is than brew? There's no way I can gauge that with my display which I've now learned shows a factory calibrated "estimate" of the brew temperature.

I guess the other quandary of mine was why the original Faema powered the thermosyphon with steam temperature water. And I think the answer here is that the optimal thermosyphon temp is a function of shot frequency. The more shots you pull, the more thermosyphon power you need to maintain group temp. The original Faema was designed for a coffee shop and probably for back to back shots you need more power and steam temp water is probably not a bad trade off. Whereas in home machines the likely shot frequency is a lot slower and therefore you move the thermosyphon source from steam boiler to brew boiler but run that hotter.

In fact I bet Ernesto Valente's design process was "I'm making a HX machine. Therefore the thermosyphon will be powered by steam temp water. What size/shape lump of metal do I need to deliver an optimal brew temp for back to back shots?. And then he played around machining different group head shapes to arrive at the E61. But inherent in the E61 shape/size design is an assumption about shot frequency and ultimately that's a compromise. The only way to not have that assumption is a Decent approach which is an altogether different beast.

Thanks all!

The flash boiling test is altitude sensitive.

I was an engineer, so had the tools to measure. Life begins at the sixth decimal point.

Display temperature reads 217°F for current coffee, Tony's Classico. Eric's thermometer reads about 195°F mid shot. I like medium roasts and adjust temperature by taste. Range on the display has gone from 210° to 225°F for outlier coffees. I seldom measure or use Eric's thermometer.

Thermosyphons were invented in the 1800s. Espresso early 1900's. Groups were pretty well defined by the late '50s.

The e61's claim to fame was slow mechanical pre-infusion so the puck is not hit with full pressure.

In certain cases, and with some (many?) E61s, you may want the steam left on even if you are not using it. If the E61 passes the brew boiler tube through the steam boiler to preheat the brew water, and you are serving multiple guests, the preheating of the water has the potential for more consistent results.

Commercially viable double boilers were introduced by La Marzocco in the early 70s. Their saturated group's temperature stability was and continues to be excellent.

It's more a question of why double boilers use E61 groups. I think the list runs out quickly past low cost and appearance.

Intra-shot temperature agility wasn't "a thing" until the last three years or so. Initial theories seem to be contradicted by explorations. Part of "lever flavor" may be due to their inherent, repeatable temperature profile.