The Multisensory Perception of Flavor: How Our Senses Shape What We Taste
As I am fond of saying, we taste more than what’s just in the food when we eat: flavor, as I and many other believe, is in the mind. Aside from how food looks, smells, sounds, and feels, the sensory information we gather from the eating environment, not to mention our own emotional state and personal beliefs, all play a role in the final perceived flavor of the food.
With my background as an experimental psychologist, I am often at odds with sensory scientists who strive to turn the human being into an objective sensory instrument. Sensory panels are trained extensively to evaluate the sensory attribute intensities as precisely and consistently as possible in controlled laboratory conditions. While this is crucially important for product development, most of us don’t eat in white sensory booths. The real world is messy, and I am specifically interested in how our conception of food is shaped by all its surrounding information: packaging and labelling, background ambience, and individual differences.
Understanding the interaction between taste and smell has important applications in the food industry. Taste provides basic information about foods, such as sweet, salty, bitter, sour, and umami. It has been suggested that up to 80%-90% of the flavor of food comes from smell. A person without a sense of smell can detect sweetness, saltiness, or bitterness in their food but would be unable to identify complex notes in it. Through evolution, the human brain has developed a complex network of sensory abilities that have allowed us not only to survive but also to thrive in diverse environments. While taste allows us to discern basic flavors such as sweet, salty, bitter, sour, and umami, smell adds an additional layer of information that enriches our sensory experience and alerts us to the quality and safety of foods. Despite its importance, the study of flavor perception has been a relatively neglected field. This is partly due to the complexity of controlling sensory stimuli and the rapid adaptation process of study subjects. This phenomenon is due to retronasal perception. In the case of soba, its aroma is too subtle to be effectively perceived through orthonasal means, especially when served cold.
Following on from ecological theories of perception, such as the one proposed by Gibson, this paper reviews the literature on the multisensory interactions underlying the perception of flavor in order to determine the extent to which it is really appropriate to consider flavor perception as a distinct perceptual system. We propose that the multisensory perception of flavor may be indicative of the fact that the taxonomy currently used to define our senses is simply not appropriate.
An innovative example of how this knowledge can be applied is Air Up, a company founded by Lena Jüngst and Tim Jäger, inspired by the book Neurogastronomy: How the Brain Creates Flavor and Why It Matters by neuroscientist Gordon M. Shepherd. Air Up uses the science of retronasal olfaction to offer a unique flavor experience through its water bottles. The magic of Air Up lies in its ability to “bring flavor” to water using flavor pods. The nasal receptors interpret this flavored air as if it were flavor, although the water itself is not flavored. Recent studies have shown that congruent food odors can be intensified by certain flavors, such as sweet, but not by others, such as bitter or sour. A recent study explored this possibility by testing two additional flavors: saltiness and umami, which signal the presence of minerals and proteins. A practical example of this phenomenon is observed in the use of dry bonito broth, rich in umami, in Japanese cuisine. This broth enhances the palatability of a low-salt diet thanks to its characteristic aroma.
The Influence of Cup Color and Weight on Coffee Evaluation
Earlier this year-before COVID-19-I gave a talk on the “Multisensory Perception of Flavor” at the EU edition Sensory Summit. As part of my talk, I conducted several live studies with audience members to investigate the influence of cup color and weight on the evaluation of coffee.
What Do We Know About Cup Color and Weight?
The correspondence between color and taste is one of the most studied. We tend to associate specific colors with specific tastes: for instance, red/pink is typically associated with sweetness, green with acidity, and black with bitterness. Not only do we tend to find red-colored foods and drinks to be sweeter (at least, in the context of sweet foods), but evidence has shown that foods tasted in red or pink bowls or cups could also taste sweeter compared to those from white containers. In another example, the same strawberry mousse tasted 15% sweeter when served on white compared to black plates. In the realm of coffee, Fabiana Carvalho, a coffee sensory researcher from Brazil (and a colleague at the Crossmodal Research Lab!), has recently published a study demonstrating that cup color can significantly influence the sweetness, acidity and liking judgements of special coffee.
Compared to color, we know much less about how the weight of servingware might affect food perception. A series of studies from the Crossmodal Research Laboratory in 2011-12 revealed that yoghurt samples served from a heavier bowl was rated as more satiating, liked more, and expected to be more expensive. A few years later, it was demonstrated that greater weight-regardless of whether it be boxes of chocolate, cans of soft drinks, or even bottles of liquid soap-increased perceived fragrance/flavor intensity as well as a consumers’ willingness to pay.
The Experiments
I will talk here about two experiments I conducted at Sensory Summit EU, one involving the manipulation of cup color, and the other with cup weight. For the color experiment, roughly half of the audience received coffee in a white paper cup while the other received coffee in a black paper cup. The cups were otherwise identical except for color. For the weight experiment, the coffee samples were all served in white paper cups, except we discretely attached metal washers to the bottom of some of the cups to make them 20 grams heavier (Fig. 1). As in the color experiment, roughly half of the audience received coffee in the normal cup while others received coffee in the heavier cup.
The brewed coffee used in both experiments were identical, from a single-estate in Tarrazu, Costa Rica. For both experiments, people first tasted the sample of coffee, then used 1-9 scales to rate the coffee’s aroma intensity, flavor intensity, acidity, sweetness, bitterness, body, and aftertaste (Fig. 2). The questionnaire was administered online via the Qualtrics platform, and people responded on their phones. After dropping incomplete responses, data from a total of 113 audience members (50 women, 63 men, aged 16-65 years, average age = 37) were analysed. A Coffee Knowledge Test (adopted from Croijmans and Majid, 2016) administered at the end of the live experiments revealed that mean coffee knowledge was 5.5 (SD = 2.0) out of 8, showing that attendants had on average a very high level of coffee knowledge.
The Results
So, did cup color alter how the coffee was rated by our expert audience? (Fig. 3) Across the sample of Sensory Summit EU participants, we found that, contrary to what we understood from previous experiments with strawberry mousse, serving the coffee in black versus white cups did not significantly influence its perceived sweetness or bitterness. However, there was a significant difference in perceived body, where the coffee served in the black cup was significantly full in body compared to the white cup. When it came to cup weight, we did not observe any differences in aromatic or flavor intensity, as we might have expected based on previous work with soap containers. However, there was a significant difference of cup weight on aftertaste, where the aftertaste was longer when the coffee was served in a heavier cup.
| Attribute | Cup Color (Black vs. White) | Cup Weight (Heavier vs. Lighter) |
|---|---|---|
| Sweetness | No significant difference | No significant difference |
| Bitterness | No significant difference | No significant difference |
| Body | Significantly fuller in black cup | No significant difference |
| Aftertaste | No significant difference | Longer in heavier cup |
What Does This Tell Us About the Importance of Coffee Cups?
The results in these live experiments demonstrate that, even for experienced coffee tasters, the color and weight of the cup influenced their evaluation of the coffee itself. More specifically, the coffee served in a black cup was rated as fuller body compared to the same coffee in a white cup, whereas the coffee served in a heavier cup was rated as having a longer aftertaste compared to in a lighter cup. We expanded on previous research by using more nuanced attributes such as body and aftertaste, which goes beyond the usual consumer questionnaire of liking (and maybe basic taste) questions. I was able to do this because most attendants were knowledgeable about coffee, as verified by the Coffee Knowledge Test.
That said, it is also plausible that experts are less influenced by extrinsic factors, being more used to judging coffee objectively. Given the relative expertise of the audience present, the question remains whether consumers might be similarly influenced in their sensory perception?
Beyond the obvious lack of ecological validity in the study (i.e., drinking coffee from paper cups in an auditorium is not the same as drinking it at home or in a café), it should be noted that one reason why we did not see more differences in the color experiment is that the white and black cups were both white on the inside, therefore creating the same stark contrast with the black coffee. How might the results be different if the cups were also black on the inside (similar to the cup color studies conducted by Fabiana Carvalho)?
I initially designed these live experiments to create a more engaging experience for the seminar attendants. The fact that audience members were able to answer questions on their phones meant I was able to show preliminary results at the end of my talk instead of waiting for months or years for publication in a peer-reviewed journal. I am a strong believer in involving the public in research, and thanks to the Sensory Summit EU, I was able to take the opportunity to test a relatively large sample (N = 113) of coffee experts at once, which would have otherwise been difficult. I am hopeful that, given the enthusiasm of the specialty coffee community, more research will move out of the laboratory in the future.