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).