The Sense of Flavour lavour is one of the most complex sensory experiences available to human beings, yet it is also one of the most frequently misunderstood. Common usage treats flavour and taste as synonyms — we speak of the taste of coffee, the taste of strawberries, the taste of salt. In fact, taste is only one component of flavour, and not the dominant one. Taste, strictly defined, refers to the sensations produced by chemical compounds interacting with receptor cells on the tongue and oral cavity, and encompasses only five primary qualities: sweetness, saltiness, sourness, bitterness, and the savoury richness known by the Japanese term umami. Flavour, by contrast, is a multisensory construction of the brain that integrates taste with olfaction, texture, temperature, and even vision and sound. The dominant contributor to flavour is smell — specifically the retronasal route by which volatile compounds released by food in the mouth travel upward through the nasal passage to the olfactory receptors. When we bite into an apple and experience what we call its flavour, the sweetness and mild acidity we detect with our tongues are only a fraction of the experience; the complex, distinctive quality we associate with apple — which distinguishes it from a pear or a grape of similar sweetness — comes overwhelmingly from the hundreds of volatile aroma compounds detected through retronasal olfaction. This explains why food loses most of its flavour when we have a cold: nasal congestion blocks the retronasal route, leaving only the basic taste sensations intact. Texture and temperature interact with taste and smell in ways that significantly alter the flavour experience. Fat is not one of the five basic tastes, but fatty foods are perceived as richer and more satisfying in part because fat carries fat-soluble aroma compounds, releasing them more slowly and extending the duration of the flavour experience. Temperature affects both the volatility of aroma compounds — warmer foods release more aroma — and the sensitivity of taste receptors: sweetness is perceived as more intense at higher temperatures, which partly explains why ice cream and cold beverages need more sugar to taste as sweet as equivalent room-temperature products. Vision plays a surprising role in flavour perception. Research by the psychologist Charles Spence has demonstrated that the colour of a food or drink powerfully conditions what flavour consumers expect to experience, and that these expectations in turn shape what they actually perceive. In a now-classic experiment, wine experts given white wine that had been coloured red with an odourless dye described it using the
vocabulary typically applied to red wine, apparently perceiving flavours that were entirely a product of visual expectation. Similarly, the shape and weight of cutlery, the colour and material of plates, and the ambient sound of the eating environment have all been shown to influence flavour perception in controlled experiments. Individual variation in flavour perception is substantial. Approximately 25 percent of the population are classified as supertasters — individuals with a higher-than-average density of taste receptor cells who perceive bitter compounds in particular with considerably greater intensity than the majority of people. Supertasters often find strongly bitter foods, including broccoli, grapefruit, and dark chocolate, aversive. At the other extreme, some individuals have very low sensitivity to bitter compounds and may find foods that supertasters find intolerable entirely palatable. These genetic differences in taste sensitivity have implications for nutrition, since supertasters tend to consume fewer bitter-tasting vegetables despite their established health benefits. The food industry invests enormous resources in understanding and manipulating flavour. Flavour scientists work to identify and reproduce the volatile compounds that define the distinctive character of natural foods, enabling the production of artificial flavours from combinations of synthetic compounds. The development of flavour enhancers — compounds that amplify existing flavour without contributing strong flavours of their own — has allowed the production of processed foods that deliver high levels of palatability with relatively low quantities of the costly natural ingredients they replicate. Critics argue that this technology has contributed to the epidemic of ultra- processed food consumption, which is associated with poor nutritional outcomes.