Despite its common usage, the term “flavor” can be difficult to define. In fact, people with different expertise tend to use the term “flavor” to mean slightly different things, even if they are all referring to food. Flavor chemists typically mean the aroma alone, many experts in sensory evaluation use flavor to mean the combination of taste, smell, and chemesthesis, while chefs tend to see flavor as a more dynamic experience that depends not only on the food per se, but also on its presentation as well the environment is which it is served. The International Organization for Standardization defines flavor as follows:
Complex combination of the olfactory, gustatory and trigeminal sensations perceived during tasting. The flavour may be influenced by tactile, thermal, painful and/or kinaesthetic effects.
However, none of these definitions really seems to fully cover the combination of sensations experienced when eating or drinking. The following is a summary of how the different senses experienced when eating and drinking interact and create the overall perception.
Taste and Smell
The results of many studies indicate the sensations of taste and smell interact. Odor ratings increase with increasing taste compound concentration, and taste ratings increase with increasing odor compound concentration. Rating increases are larger for harmonious taste-odor pairs, or taste-odor pairs that are typically encountered together, than for unusual taste-odor pairs. Adding sucrose to fruit juices will increase sweetness, decrease bitterness and sourness, as well as decreasing unripe odor ratings and increasing fruit odor ratings.
Studies have shown that some compounds typically thought of as taste stimuli, such as salt (NaCl), citric acid (sour), and quinine (bitter), can be irritating at moderate and high concentrations (Ever go swimming in the ocean? Ever get salt water in your eyes? Ouch!). Similarly, some odor compounds can elicit activity in the trigeminal nerve (which is associated with the perception of irritation), without creating sensations of burning or stinging, and can contribute to the perceived odor intensity. Irritants can alter the perceived intensity of odors and tastes, and tastes and odors can alter perceived irritation.
There is an increase in volatile components being released from a sample as it is heated. As a result, odors can become more intense as a given sample is heated. A food might contain volatile compounds that are below threshold levels at lower temperatures, but that are detectable as the food is warmed. When odor ratings are made orthonasally (by sniffing foods and beverages), ratings rise as the temperature rises. When odor ratings are made retronasally (once the samples are in the mouth), odor ratings rise with increasing temperature for solids but not for liquids. This is likely because once placed in the mouth, liquids more quickly come to the same temperature (body temperature) than do solids.
The impact of temperature on taste is less clear. Recent work has shown that temperature itself can elicit taste sensations, although it is unlikely the gustatory system was intended to respond to temperature. But parallels exist in other senses where a different type of stimulation can give rise to sensation. For example, if you press the heel of your hands gently on your closed eyes, you can see flashes of light. This does not mean that our eyes were designed to respond to pressure, but that an inappropriate stimulus can elicit a weak response from a sensory receptor by triggering cascade reactions within the receptor. Temperature seems to affect the gustatory system in a similar fashion.
Although sight is comprised of more than the perception of color alone, the visual impact of food and beverages on taste, smell, and flavor perception has focused on color. Uncolored and miscolored foods and beverages are identified correctly less often than appropriately colored items. This is likely because individuals seem to associate certain flavors with specific colors and when the colors are altered, identification is decreased. The stronger the color-flavor association is, the greater the impact of color tends to be. The impact of a particular color on a given taste has been inconsistent across studies, probably because tastes like sweet, sour, salty, and bitter do not have strong associations with particular colors. While we associate the color green with lime flavor, no particular color is associated with bitterness, saltiness, etc. Another general trend is that as color level increases, taste and flavor intensity increases. This is maybe due to our familiarity with beverages made from powders or concentrates, which become weaker in flavor and taste as they become weaker in color.
The nature and amounts of the volatile odor and nonvolatile taste compounds are major determinants of flavor. The texture of a food or beverage controls the accessibility of these compounds to taste buds and olfactory neurons, with that availability depending upon the breakdown of the food or beverage. Increasing a food or beverage's texture slows the diffusion of components to the sensory receptors while decreasing the texture will increase the rate of diffusion. This means that two items with the same amount of taste and smell compounds but different texture will differ in their perceived intensity and onset time, where the thicker-textured item will take longer to reach its peak intensity and its peak intensity will be lower than the other product's peak intensity. Recent research suggests tactile sensations themselves, not just the changes in the diffusion of taste and odor compounds with different textures, can modulate the perception of taste and smell.
While sound contributes to the experience of eating many foods, like potato chips, pretzels, and other crisp and crunchy foods, there is no evidence that it interacts with the perception of taste, smell, or chemesthesis. While the definitive research remains to be done, the interaction of sound with the chemical senses seems unlikely.
For more information, see Delwiche (2004), Food Quality and Preference