Color, weight, rim thickness: three very unequal beliefs
The trade takes three propositions for granted. The white cup makes coffee more bitter. A heavy cup makes a better impression. A thick rim gives body. They are not worth the same at all.
Color has been measured four times, with results that overlap only in part. The founding study, by Van Doorn, Wuillemin and Spence in 2014, starts precisely from a barista's remark: coffee served in a white cup would seem more bitter than in a clear glass. On eighteen volunteers divided into three groups of six, only one attribute moves, intensity, judged stronger in white than in glass. Bitterness does not move, even though its means range from 36.2 in glass to 55.7 in white: the gap is wide, the sample too small to settle it.
The same authors repeat the test with thirty-six volunteers and identical glasses fitted with colored sleeves. This time it is sweetness that moves, the coffee being judged less sweet in white, and intensity no longer stands out. Color therefore acts, but the internal replication changed target, which is the sign of a real but unstable effect rather than a solid one.
Weight has never been tested on coffee. The review by Spence and Carvalho states that it knows of no publication on the weight of the coffee cup. What exists is adjacent: Kampfer and coauthors glued 60 grams under soda cans, and the same drink is judged better in the heavy can; Maggioni and coauthors obtain the same direction with sparkling water. Nothing has been redone with coffee.
Rim thickness is the least supported of the three, and yet it is the one asserted with the most assurance. Two studies come near it, neither establishes it, and the detail is worth reading.
Why rim thickness proves nothing, and the color figures
Van Doorn and coauthors showed eight cups online to 309 people in China, Colombia and the United Kingdom, varying three characteristics: height, diameter and rim thickness. All the reported effects concern height and diameter. Low, narrow cups announce a more bitter, more aromatic and more intense coffee, wide ones a sweeter coffee. Rim thickness shows up in no effect. A reservation from the authors themselves: nobody drank anything, these are expectations raised by images.
Ichimura and coauthors had people taste: fifty-six subjects, unsweetened cold green tea, a glass with a thin rim of 1.2 millimeters against a thick rim of 2.8 millimeters, blindfolded. The thick rim increases perceived sweetness, the thin rim bitterness. Three reservations, all decisive, and all formulated by Spence himself in his 2024 review: the effect appears only in an analysis that had not been preregistered, that is, declared before the data were seen; the thickness was confounded with the weight of the glass, 159 grams against 228; and when that weight difference was neutralized in a subsequent study, the effect disappeared. It was moreover not coffee.
On the perceived body of coffee as a function of rim thickness, there is therefore no published measurement.
The other color figures, for the record. Guéguen and Jacob had 120 French people taste the same coffee in four colored cups, asking them which was the hottest: red 38.3 percent, yellow 28.3, green 20.0, blue 13.3. That concerns perceived temperature, not taste. Carvalho and Spence then tested 457 consumers in Brazil on four colors and two contrasting coffees: before tasting, pink signals sugar, green and yellow acidity; after tasting, liking drops when the cup promised something other than what the coffee delivers.
This is perhaps the most useful result of this whole literature, and it is not about taste: it is about the promise.
One last measurement, on texture rather than material. Lago and coauthors had 96 participants taste iced tea in cups with a smooth, neutral or rough surface. The smooth-finish cup was rated significantly sweeter than the other two, at identical actual sweetness. The surface one touches therefore matters, which is not the same thing as the material that touches the coffee.
In this plateThe 15 sections
- 01Three things we must stop confusing
- 02The handleless cup, and the holder that takes on the status
- 03The Ethiopian sini, and a ceramic route older than coffee
- 04Europe does the opposite: it adds a handle and removes the holder
- 05The tazzina, and what the texts really say
- 06Material: the question asked at the counter is the wrong one
- 07Preheating, porosity, and two beliefs to sort out
- 08Shape: the only solid measurement in the file, and its counterexample
- 09Color, weight, rim thickness: three very unequal beliefs
- 10The cupping bowl, the only coffee vessel to be standardized
- 11Contemporary shapes: what we buy is a well-drawn hypothesis
- 12Asia, and vessels made for the nose
- 13The disposable cup, which is a plastic object
- 14The largest survey ever made, and why it does not settle the matter
- 15What can be said in the end, and what cannot
The table of contents, with the first sentence of each section