The cupping bowl, the only coffee vessel to be standardized

Extraction first. Liang, Chan and Ristenpart measured on their cupping trials an equilibrium yield of 23.9 percent, within 0.6, on caffeinated coffees, and 22.2 percent on decaf. That is above the 18 to 22 percent window aimed at for a beverage. How they measured must be stated: the coffee was brewed in a twelve-ounce glass, about 180 grams of water at 99 degrees on 9 to 14 grams of grounds, crust broken at the fourth minute, then ten more minutes before filtration.

The figure therefore describes the beverage at the end of a session, not at the moment of the first spoonful. The authors themselves point out a possible bias, these coffees having been brewed on the very day of their roasting, without degassing.

The same work incidentally gives a result that justifies the width of the normative ranges: at equilibrium, in full immersion, the yield is insensitive to the brew ratio, the grind size, the roast degree and the temperature between 80 and 99 degrees. A bowl of 210 milliliters and a bowl of 340, dosed at the same ratio, therefore give about the same beverage. What counts is the identity among the cups of a session, not the absolute value.

Temperature next. The SCA protocol has the tasting run from 71 to 21 degrees. The ISO standard, on the same product, skims the surface grounds and has the tasting between 50 and 55 degrees. The two standards do not put the same liquid in the mouth.

Finally, the direct comparison. Di Donfrancesco, Gutierrez Guzman and Chambers had thirteen coffees from Huila evaluated by two routes: four cuppers following the SCA protocol, and six trained judges tasting the filtered beverage served between 60 and 65 degrees. The two data sets overlap little. Only one pair of attributes stands out positively, and two correlations are negative. The cuppers moreover used 59 different terms, of which only four were used by more than two evaluators to describe the same coffee. The authors conclude that the two methods cannot substitute for each other.

This last result should not be over-interpreted, as it changes the vessel, the brewing, the temperature and the panel all at once: the share of the container cannot be isolated in it. It establishes only this, which is enough: the cupping score and the profile of a cup drunk are not the same object.

And there remains a hole, the most astonishing of the plate. No published experiment varies the geometry of the cupping bowl alone. The trade's phrases about the wide bowl that cools fast or the tall bowl that holds the aromas are consistent with physics, but they have not been measured on this object.