THE PROCESS IN MOTION

Three cups, twenty-three minutes

Start the scene or choose a stage. The animation simplifies the mechanism; what follows gives the details and the available references.

▶ Play the process01Three ounces in three cups02At the start, the ceramic takes the most03Twenty-three minutes later04Preheating is not enough

Three ounces in three cups

An engineering firm pours three ounces of espresso into three cups, a 17.4 gram cardboard cup, a 553 gram ceramic and a polystyrene cup, and records the temperature for twenty-three minutes. It is not a reference, but the test follows the reasoning of thermal mass.

Read the stages without animation

1. Three ounces in three cupsAn engineering firm pours three ounces of espresso into three cups, a 17.4 gram cardboard cup, a 553 gram ceramic and a polystyrene cup, and records the temperature for twenty-three minutes. It is not a reference, but the test follows the reasoning of thermal mass.
2. At the start, the ceramic takes the mostThe coffee starts at 81.6 °C in the cardboard, which takes almost nothing from it, and at 80.5 °C in the polystyrene. In the ceramic, it starts lowest, at 78.6 °C, because its thermal mass exceeds that of the coffee several times over.
3. Twenty-three minutes laterThe cardboard ends lowest, at 38.9 °C, because it insulates nothing; the ceramic at 41.7 °C; the polystyrene highest, at 46.6 °C, because it is light and insulating at once. Only the start and the end are given here: between the two, the curve is not provided.
4. Preheating is not enoughA hot water rinse can bring the ceramic only to 57.4 °C, against 77.4 °C for the cardboard: its mass keeps it from being preheated. No published, peer-reviewed measurement quantifies the difference in the cup between cold service and preheated service.

To remember: the heavy cup takes at serving, the insulator keeps afterward; the light cup takes nothing and keeps nothing.

Read the full article and its sources ↓

Preheating is constantly recommended and almost never quantified. Only one standard mentions it, ISO 6668 on the preparation of green coffee samples, and it merely notes that warming the cup while the water boils may be desirable or necessary. It is a note, not a requirement, and it gives no value.

An engineering firm published a comparative test which, though not a reference, follows exactly the reasoning of the previous chapter. Three cups receive three ounces of espresso, with readings over twenty-three minutes. The 17.4 gram cardboard cup starts at 81.6 degrees and ends at 38.9: it starts highest because it takes almost nothing from the coffee, and it ends lowest because it insulates nothing.

The 553 gram ceramic starts at 78.6 and ends at 41.7: it starts lowest because its thermal mass exceeds that of the coffee several times over. The polystyrene starts at 80.5 and ends at 46.6, because it is light and insulating at once.

The same work calculates that a hot water rinse can bring the ceramic cup only to 57.4 degrees, against 77.4 for the cardboard. The ceramic mass is such that it does not let itself be preheated easily, which is the exact flip side of its advantage. No published, peer-reviewed measurement of the difference in the cup between cold and preheated service was found, and the figures that circulate come from commercial sites, with no protocol.

As for porosity and the transfer of taste from one coffee to the next, the commercial formulation is almost always false. It is not the body of the cup that touches the coffee, it is the glaze, which is a layer of glass. As long as it is continuous, even a very porous earthenware lets nothing through. The problem appears when the glaze cracks, a defect called crazing: a network of microcracks then opens capillaries toward the body, and that is where stains and residues settle. No instrumental measurement of aroma carry-over in a crazed cup was found. The claim is plausible and not measured.

Where regulation does settle the matter, on the other hand, is leaching. The 1984 European directive on ceramic articles in contact with food sets, for a hollow article of under three liters, migration limits of 4.0 milligrams per liter for lead and 0.3 for cadmium. A compliant glaze is a verified barrier, not a promise.

ISO 6668:2008, clause 8.5; Glew Engineering, “Thermal Analysis of Espresso Cup Materials,” parts 1 and 2; ASTM C373-18, water absorption measurement method; Directive 84/500/EEC as amended by Directive 2005/31/EC