We know that information travels to our chemical senses (taste and smell) much more slowly and lingers after the stimulus has gone. Simple logic will therefore suggest that the time-course of the transduction is less critical than for hearing and vision. A matter of taste Gustation (taste) is relatively simple in that it encodes only five dimensions of the stimulus: sourness, sweetness, saltiness, bitterness, and ‘umami’, which is a taste similar to monosodium glutamate. The receptors for taste – our taste buds – are on the surface of the tongue. Different types of chemical molecules interact differently with the taste buds specialized for the five different taste sensations.
Salty sensations arise from molecules that ionize (separate into charged ions) when they dissolve in the saliva. Bitter and sweet sensations arise from large non-ionizing molecules. Sour tastes are produced by acids, which ionize to give a positively charged hydrogen ion. The umami taste is produced by specific salts such as monosodium glutamate. The mystery of smell Olfaction (smell), on the other hand, is shrouded in mystery. We do not understand much about how the receptors in the nose respond to different trigger molecules carried in the air that we breathe. It seems a fair assumption that these airborne molecules interact with specific receptors to elicit certain sensations. Unlike the other senses, there is a vast array of receptor types, possibly up to 1000. Subjectively, it seems that smell elicits certain memories and is notoriously hard to describe verbally. The flavour of a food is conveyed by a combination of its smell and taste. Flavours re described by a complex set of references to substances that possess elements of these flavours. For example, wine experts talk about the ‘nose’ of a wine, meaning its smell; the early taste sensation is the ‘palate’, and the late taste sensation is the ‘finish’. The tasting terminology is esoteric and has a poetic quality, with words like ‘angular’, ‘lush’, and ‘rustic’.