Adrian,
I've been struggling with the choice of Vivaldi Mini and Duetto. Am trying to get information on intra-shot temperature. I have an Andreja Premium now and have a digital thermometer in the E61 group head. I'm trying to figure out how much of the drop in temp during a pull is due to the HX vs. due to the large external group head itself.
What did you wind up buying, and did you ever get the info on intra-shot temp for the two machines (you said it was available for the Duetto but I haven't been able to find it)?
Thanks



...split from The Effect of Nonvariable Preinfusion on Intrashot Temperature Stability by moderator...

I own the La Spazziale Mini Vivaldi II. I measured the intrashot temperature with a simple modified portafilter. The temperature is reasonably stable during the shot. Preinfusion methods of various physical types, such as those offered by the Vivaldi or Duetto (E61) yield a similar improvement in intrashot temperature stability, although the slope of the curves are characteristic of the physical devices involved. The Duetto information can be found here.

There is no question that the profile curve of the intrashot temperature change is linked to the flavor of the espresso produced. My opinion on this is that this is a minor effect when compared to grind, dose, distribution, etc. It is probably more important to provide temperature stability because it eliminates a variable more than anything else, since the effects of the other variables can then be more clearly discerned. That is to say, it won't make a "sink shot" into a "god shot" but it will allow you to explore the flavor nuances of your espresso when it is properly made.

I think this has been demonstrated fairly well by the sometimes counterintuitive results obtained with the Dalla Corte Mini. We cannot view these machines as simple checklists of parts. They behave as complete and idiosyncratic systems. Frankly any of these machines is going to give you a good cup of espresso and allow you to have a very high degree of control over the extraction process.

I personally opted for the La Spazziale since it is very easy to use in a push-button idiot-proof way. I chose this over the Duetto because in a certain sense the Duetto is an answer to the question: "Is there a PID-controlled dual boiler E61 group machine?" but this is not necessarily a logical question to ask.

In your case, already owning an E61 group machine, if you have a great deal of familiarity with it, and simply wish to eliminate the HX aspect, the Duetto would be a reasonable choice. What you really have to do is ask what you want to get out of your espresso machine and choose one based on that idea.

Here's a link to a pretty comprehensive analysis of the Duetto that examines intra shot stability and the effect of the HX.
http://www.home-barista.com/espresso-machines/temperature-study-of-alex-duetto-t7950.html

[edit] sorry, didn't notice adrian already posted link. Shouldn't post before first cup of coffee.[/edit]

Between those two machines, things like looks, usability and price will quite probably prove to be more important than intra-shot temperature stability (which will be good with either). I would recommend getting the one that best fits your kitchen, routines and wallet. Differences in temperature stability will be dwarfed by how those machines are used, so it's best to get the one you are personally more happy with.

I have two machines with identical groups, one HX PID and one DB. Just when I think one machine is showing a decided advantage on a particular coffee, a change of /[in a] coffee nullifies the advantage.

Intra shot stability undoubtedly has an effect, but it is also probably extremely difficult to quantify.
The images below show two shots, one 20s and one 30s measured with a TC in the center of the puck on the PID HX.



Same shots with reduced temperature scale. Notice the difference in the group profile on the 'denser' puck.
[Note : these informal measurements were not rigorously controlled.]



Choosing a machine based on a graph might be a fool's errand.

Vive la différence !