Four things stand up at the end of this plate, and they are not the ones expected at the start.

The first is thermal, and it is the best established. An ordinary porcelain cup weighs, thermally, about as much as the espresso it receives, so that it takes from it half of its gap to ambient temperature in the seconds of serving. Preheating is therefore not an affectation, it is the only gesture in this whole plate whose effect can be calculated and counted in tens of degrees. And a light preheated cup is better than a heavy one taken from the shelf.

The second is perceptual, and it is small. The shape of the vessel shifts judgments by a few tenths of a point on ten-point scales, among tasters in a single session, amateurs and professionals alike. This effect is real, it is measured on 276 people, and it almost disappears with a trained panel that compares. One must be able to hold both results together rather than choose the convenient one.

The third is that the promise counts more than the physics. The most solid result of the whole literature on color is not that a yellow cup makes a coffee more acidic: it is that liking drops when the cup promised something other than what the coffee delivers. The vessel announces, and the drinker compares. It is a mechanism of expectation, not a mechanism of taste, and it is probably the essence of what a container does.

The fourth is a finding about method. On the points where the trade asserts the most, it does not measure. No experiment varies the geometry of the cupping bowl alone, though it is the only standardized coffee vessel. No maker of tasting glasses publishes the two diameters that would make it possible to verify the physical argument it invokes. No measurement of the volatiles above the liquid exists for a commercial coffee vessel, though it is the simplest experiment of the lot.

No blind sensory measurement exists on coffee in a metal vessel. And on perceived body as a function of rim thickness, which is the most repeated phrase of the trade, there is nothing at all.

What remains is what has been known for three and a half centuries and has never been refuted: a narrow opening retains the volatile essence of the brew. Dufour wrote it of a coffee pot in the seventeenth century. Nobody has yet measured it on a cup.