In Australia alone, around a billion cups of coffee are consumed in cafés, restaurants and other outlets each and every year [1]. Even Britain, a nation famous for its fondness for tea, has, in recent years, seen a dramatic rise in its coffee consumption, with an estimated 70 million cups drunk each day [2]. Given the economic incentive to keep consumers drinking coffee, café owners, restaurateurs, crockery designers and manufacturers ought, presumably, to be interested in anything that can help to enhance the multisensory coffee drinking experience for their clientele cf.[3].

The idea behind experiment 1 came about serendipitously. During a conversation between the first author (GV) and a barista, the latter reported that when coffee is consumed from a white, ceramic mug, it tastes more bitter than when drunk from a clear, glass mug instead; note that these two mug types are amongst the most commonly used vessels to serve coffee in Australian cafés and restaurants. In the present study, we therefore sought to establish the validity of this claim which, to our knowledge, has not been described previously. Indeed, as recently highlighted by Spence and Wan [4], there is a paucity of research on the psychological impact of the receptacles that we use to drink from.

The notion that the colour of the receptacle/plateware can impact taste/flavour perception might relate to Piqueras-Fiszman et al.’s [5] research putatively showing that colour contrast resulted in a red, strawberry-flavoured mousse presented on a white plate being rated as 10% sweeter and 15% more flavourful than when exactly the same food was presented on a black plate, see [6, 7] for an extension of this work; see [8] for an explicit attempt to evaluate the colour contrast account. While contrast represents one plausible explanation for such results, it is important to note that there are also several other possible mechanisms (e.g., priming) that may explain the influence of product-extrinsic colour on taste/flavour ratings. Taking the principal of colour contrast one stage further, and given the conversation with the barista, it was proposed that brown may be associated with bitterness (or, perhaps, is negatively associated with sweetness [9]). If taste were to be affected crossmodally by colour contrast, then coffee that is tasted from a white mug should be rated as somewhat more bitter than exactly the same coffee when consumed from a transparent mug instead.

It is possible that another contrast mechanism (i.e., simultaneous contrast) might affect the perception of taste [10, 11]. Here, if light, opaque, milky brown coffee were to be associated with bitterness, then a light blue mug/surrounding should intensify the brown of the coffee because blue is brown’s complementary colour [6, 12]. This, in turn, would be expected to elevate ratings of bitterness relative to the same coffee when served in a transparent mug. Some famous examples of the use of simultaneous contrast are Heinz’s™ use of a greenish-blue can to set off the red-orange colour of their beans and sauce and Cadbury’s™ use of purple packaging to enhance the colour of their chocolate.

Although many studies have been published on colour-flavour interactions over the years, see [13] for a review, very little has been published to date specifically looking at crossmodal influences on the perception of coffee. This absence is surprising given, as we saw above, how many cups of coffee are drunk every day. In terms of the limited research that has been conducted specifically in this area, Favre and November [14] offered 200 people coffee from four different jars, i.e., brown, red, blue and yellow. Seventy-three percent of the participants reported that the coffee served from the brown container was too strong, whereas 80% of women felt that the coffee served from the red receptacle had a richer, fuller aroma. The blue jar suggested a milder aroma to most and the coffee in the yellow container was rated as coming from a weaker blend.

Meanwhile, Guéguen and Jacob [15] had 120 people drink coffee from four different coloured cups (blue, green, yellow and red). The participants had to indicate which coffee was the warmest (in terms of its temperature). Thirty-eight percent of the participants reported that the coffee served from the red cup was the warmest, followed by yellow (28.3%), green (20.0%) and, finally, blue (13.3%). Note that these differences were statistically significant. In summary, the colour of the cup can be added to the list of factors that have now been demonstrated to influence various aspects of the coffee drinking experience. This list also includes whether or not the coffee had an eco-friendly origin [16] and any branding cues [17].

Based on previous work and anecdotal evidence, we explored the impact of the colour of a receptacle on people’s coffee drinking experience. If extrinsic cues influence a consumer’s experience of coffee, and if taste is affected by contrast effects, coffee tasted/drunk from a white mug should be rated as more bitter than from a clear mug instead. Given Piqueras-Fiszman et al.’s [5] and Stewart and Goss’ [7] work with strawberry mousse and cheesecake, respectively, we thought that it is possible that the brown-bitter association might be enhanced by colour contrast. However, and with regard to the colour of coffee and the colour of the immediate surroundings against which it is presented, simultaneous contrast might be at work. Specifically, the brown of the coffee may be intensified if the coffee is served from a light blue mug. It should be noted that factors other than contrast effects can influence perception. For example, the cup in which the coffee is served may affect us as a function of our perception of the general properties of the cup (i.e., cheap vs. expensive [18], flimsy vs. strong [19]). We have attempted to control these potentially confounding variables in the present study. That said, and to borrow from Piqueras-Fiszman et al. [5], if the colour of the mug affects the way in which people perceive the colour of the coffee, and the colour of the coffee affects the perception of flavour, then the colour of the mug (and any contrast effect that it elicits) would be expected to influence the perceived properties of the coffee (e.g., bitterness).