> The bottom line of the team’s experiments and mathematical modelling is that to get the most reproducible shots just use less coffee and grind it more coarsely.

This seems to go against conventional wisdom, which says that less coffee will reduce brewing time and a coarser grind will also reduce brewing time, and consensus seems to be that you want a brewing time somewhere between 20 and 30 seconds. Or did I misunderstand something?

Anyway, the reasoning seems sound, so I'm going to have to give this a try.

For an entire book about the topic, see "The physics of filter coffee" by Jonathan Gagné.

Also

> This can be achieved using an espresso machine (figure 1), or with smaller contraptions at much lower pressures such as a moka pot or AeroPress.

Please, just stop. They're not even remotely close.

In the pour-over section, the authors hit on a good point about height and creating a vortex in the slurry. Water temperature and flow rate are important variables too. Combined with the coffee grounds' quality (i.e. grind consistency) and whether it has fines or lots of chaff will also dictate how long it takes to draw down and therefore whether the pour height's effects will change if static.

I do like the advice grind coarser and extract with more water -- that's made my V60 coffee quality fairly consistent, but everyone's mileage will vary based on how they like their coffee and the roast profile.

There are so many other variables that didn't get a mention: Coffee varietal

Water hardness (and even which other ions are present in the water) and its effects on acids and other compounds that highlight certain varietal's defining characteristics.

Vessel temperatures.

The filters used (materials, paper thinness).

Pouring patterns (circular, concentric, hypotrochoid, more?)

The filter shape and material.

Even the grinder used conical vs. flat burrs and high RPMs vs. low RPMs creates palpable flavor profile differences.

The rabbit hole goes deep and continues to expand.