The graphical analysis of intrashot temperature stability has been documented for several modern espresso machines, including the La Marzocco GS3 and the E61-based Alex Duetto, each of which has a form of preinfusion. In general, we have seen that temperature stability is restricted to a range of about 2 degrees C during a shot, and that the total amount of variation decreases with shot duration.

The La Spaziale Mini Vivaldi 2 has a unique form of fixed preinfusion. Before doing an analysis myself, has anyone else had experience with intrashot temperature stability in this setting?

Thanks for your help!
Adrian

A convex temperature profile absolutely makes sense if one is having a discussion about roasting, but its purpose in extraction is less clear. Extractable solutes in coffee grounds will be removed (as they would be in any chemical extraction) above a given temperature. That is to say, all solutes removed at lower temperatures will be removed at a higher temperature as well.

A weak argument can be made that certain extractable elements will undergo chemical decomposition at a higher temperature and their presence will be preserved by the lower temperature portion of the curve. This is unlikely as we are dealing with relatively low temperatures and an aqueous solution.

More likely, one can argue that a convex curve will reduce the fractional amount of extracted solutes that would come off the column at higher temperatures, broadening the flavor profile somewhat. This becomes an issue in coffee blends with a narrow "ideal" zone, where a tall convex curve would yield espresso that is simultaneously sour and bitter.

Of course, all extraction temperature curves are in reality generally convex, with overlying temperature instabilities that can be greater or lesser. I am postulating that a flattened curve will be more likely to yield a sweet cup of espresso for more espresso drinkers, albeit perhaps less complex (and ideally one could control this curve for each individual blend).

More to the point, I am suggesting that fixed preinfusion reduces the risk of channeling but may increase the average intrashot temperature variation, altering the flavor profile of the resultant cup in a predictable way that may or may not be desirable.

another_jim wrote:The desirable thing is that the intra-shot profile is repeated for every shot.

Of course, as usual, Jim, you are dead on with this comment.

drdna wrote:... intrashot temperature stability ...

... has to be one of the most confusing terms in espresso. IMHO there ain't no such animal. Espresso extraction is a dynamic system that never achieves equilibrium during a shot.

At best, you can deliver hot water to the top of the puck at a specific brew temperature. But the puck starts out at room temperature and the grinds absorb heat from the water. This will always generate a temperature gradient in the puck, with higher temps at the top and lower temps at the bottom. As the shot progresses, temps will rise throughout the puck, up to (but never past) the brew water temp.

drdna wrote:More likely, one can argue that a convex curve will ... broaden the flavor profile somewhat. This becomes an issue in coffee blends with a narrow "ideal" zone, where a tall convex curve would yield espresso that is simultaneously sour and bitter.

This makes a lot of sense to me. To my knowledge, nobody has done a comprehensive study on this subject - kinda amazing, given the importance of brew temp in making espresso. There may be an optimal range of extraction temps for most blends, and it's possible that extraction throughout the entire optimal range yields a better taste than extraction in just one part of the range.

drdna wrote:Of course, all extraction temperature curves are in reality generally convex...

HX machines tend to deliver a "humped" brew temperature profile, but I don't believe this is true for single (or double) boiler machines.

drdna wrote:...I am suggesting that fixed preinfusion... may increase the average intrashot temperature variation...

I fail to see why this would be the case. If anything, preinfusion would prewarm the grinds and reduce the intrapuck temperature variation mentioned above. Why would the type of preinfusion make any difference?

The question was pretty simple:

The La Spazziale Mini Vivaldi 2 has a unique form of fixed preinfusion. Before doing an analysis myself, has anyone else had experience with intrashot temperature stability in this setting?

Naturally, you can post whatever you want about the terminology used, the effects and desirability of particular temperature profiles, etc, but that doesn't answer the question that was asked.

Cheers,

Luca

drdna wrote:The La Spazziale Mini Vivaldi 2 has a unique form of fixed preinfusion.

Please explain.

Hi!
It's a cylinder with a piston on a spring attached to group before dispersion block.
Here are two pictures.
If you don't know how the device works you can read these four posts.
It's not that hard to explain, but better to point there because of question-and-answer style which explains it step by step.

CoffeeOwl wrote:If you don't know how the device works you can read these four posts.

Thanks, Pawel.

drdna wrote:The graphical analysis of intrashot temperature stability has been documented for several modern espresso machines, including the La Marzocco GS3 and the E61-based Alex Duetto, each of which has a form of preinfusion. In general, we have seen that temperature stability is restricted to a range of about 2 degrees C during a shot, and that the total amount of variation decreases with shot duration.

The La Spazziale Mini Vivaldi 2 has a unique form of fixed preinfusion. Before doing an analysis myself, has anyone else had experience with intrashot temperature stability in this setting?

Thanks for your help!
Adrian

There are two basic problems in studying anything like this, which are:

You have to define precisely what it is you are trying to study and how you will study it, and then after defining how you will study it you must evaluate the results of what you studying in a way that will stand up to some sort of "scientific scrutiny."

The first is possible, but doing only the first makes it likely that the response to these results will be "So What?

The second is also possible but unless the testing is very limited to a very specific and repeatable question, the observations will not be believable and when someone else tries to repeat a similar study they will not get the same results.

As one of the few people on the coffee internet (with Jim Schulman) who has actually attempted to do this sort of research, my suggestion would be to have a very narrow hypothesis to test that can be tested with a simple comparison between two differing conditions. An example would be, for example, to hypothesize that one sort of preinfusion produced "tastier" shots than another. You would then need a "testbed" that would enable you to vary only that factor, with all other things being kept equal.

Once you succeeded in producing a test condition that could reliably produce the two (or three, at most) conditions you were testing, then you would need to verify that you were in fact producing the results desired, and then to test them in a blind or at least semi-blind condition that would enable you to say that one was "better" or "tastier" than the other.

Anything short of this will produce information that may be interesting, but that will probably not shed any real light on whatever it is that you want to evaluate. A casual perusal of this and other boards will show many attempts to study various factors in producing espresso shots, and with hardly any exceptions, very little or anything productive seems to ever come out of such "evaluations" unless they are very tightly focused.

ken

I absolutely agree with you, Ken. However, at this point it may be to early to even form a hypothesis, let alone consider the technical difficulty in isolating and changing a single variable. My feeling at this point is simply that there is too little data out there. If we see consistency in the characteristic curves generated in fixed preinfusion systems, then I think we can begin to consider what questions to ask.

Adrian

drdna wrote:...I am suggesting that fixed preinfusion reduces the risk of channeling but may increase the average intrashot temperature variation...

With a pressurized boiler whose water is greatly above desired brew temp, and so requiring a massive brass bell heat sink to mitigate the excessive temperature: if the puck is first warmed by the preinfusion, then the peak temperature at the puck/in the puck/throughout the puck could be significantly higher than it would have been without a preinfusion.

With an unpressurized boiler ("kettle") whose water is just a few degrees above desired brew temp, and so not requiring a massive heat sink (stainless steel collar suffices), the higher peak temperature after preinfusion will be far less alpine.

The unpressurized kettle would permit designs that allow for user-defined preinfusion times. Time being an important factor in solubility, I'd opt for a machine that allows as long a preinfusion as I might want, without the risk of, say, the HX heating up too much as I lingered during this phase, or the puck getting too warm. The hotter the machine, the more precipitous the slope of misfortune.

Conclusions drawn from a study of one class of machine (boiler) may not apply to other classes of machine (kettle).

drdna wrote:The graphical analysis of intrashot temperature stability has been documented for several modern espresso machines, including the La Marzocco GS3 and the E61-based Alex Duetto, each of which has a form of preinfusion.

GS3 can have pre-infusion but can also have no pre-infusion (up to you).