Smell

Smell—also called aroma or olfaction—is often considered the most important of the three components of flavor. It is the most predominant, and is certainly the most complex. Humans perceive only five basic tastes, but they can smell hundreds—even thousands—of distinctly different aromas. Most aromas themselves are complex. For instance, there is no one single coffee molecule. Instead, coffee aroma consists of hundreds of separate chemicals.

To produce smell, molecules must be volatile (that is, they must evaporate and escape from food) to reach the top of the nasal cavity. This is where millions of olfactory cells (smell receptors) are located. The olfactory cells are immersed in mucus, which consists mostly of water, so aroma molecules must be at least partly water soluble as well as volatile. To reach the olfactory cells at the top of the nasal cavity, molecules travel either directly from food through the nose (ortho-nasal pathway) or up the back of the throat (retronasal pathway) as food is chewed and warmed in the mouth (Figure 4.6).