When we think of one of our favorite meals, we usually remember the taste in our mouth. But when you take a close look at what makes a taste special, most of the action is taking place in our nose and brain.
We begin by understanding sensory nerves, which are a combination of a receptor and transmitting nerve. The transmitting nerve’s role is relatively simple: it’s a wirelike cell that sends electrical signals back to the brain.
But the receptor end is more specialized. Every set of receptors has extraordinary properties to detect a single signal, and only if that signal is detected does the wire end of the sensory nerve initiate electrical firing to the brain. Receptors come in a variety of types that are triggered to fire when hit by light, the vibrations of sound, or even touch.
We have several thousand sensory nerve cells that we know as taste buds, and although they are mostly on the tongue, there are some on the roof of our mouth and possibly even one type in our lungs. These thousands of taste buds fall into five categories, as each bud can fire only in response to one of five signals: sweet, sour, bitter, salt, and umami.
However, even with this specialized role to respond to flavor, taste buds alone don’t account for our fondest food experiences. Our nose plays a major role.
The special sensory nerve receptors of the upper nose are the only sensory nerves that connect directly to the cerebral cortex. All others go through intermediary nerve structures, which is why smells can trigger very deep parts of our minds.
In contrast to the five categories of taste buds, there are about 1,000 separate types of receptors in the olfactory nerves of the nose. And about 3% of our entire genetic code is devoted to making them. We still do not know the whole story of our sense of smell, but we do know that each of these olfactory receptors responds to one type of chemical in the air of the upper nose.
So, let’s say that you are enjoying a very fine and complex dish that contains countless flavors. One sniff will set off many, many olfactory receptors, each delivering a signal that a specific flavor has been detected. The brain then reassembles the various signals from each discrete receptor to actually create an overall sense of the flavor. The current estimate of how many different, distinct aromas the olfactory power of the brain can distinguish is rising rapidly—1,000 trillion and counting.
An article called “Altered Tastes” by Maria Konnikova, published in The New Republic in February, featured the extraordinary possibilities that open up from our experience of eating and tasting. It turns out that our brains are fairly accurate about sizing up just how many calories are in a bite of food, but become quite confused with flavor hints, such as color. For example, it is hard for someone to detect an orange flavor in a green food.
Other fascinating influences on flavor include encapsulation (where a burst of flavor is released by a quick crunching bite), temperature (food can taste sweeter if it is warmer, even if little or no sugar is present), delivery (flavor can actually vary if delivered by the right or the left hand), and environment (music and visual cues can change our experience of a food).
But that’s not all—coolness and hot spiciness are sensations experienced by a set of nerves entirely distinct from the taste buds and the olfactory nerves. These nerves are called chemesthetic, and the cool of mint and the heat of Tabasco appear to be related to a chemical trick. The sensory nerves that fire when temperature drops and when it rises, fire when around these compounds.
Curiously, neither mint nor jalapenos actually change the temperature of the mouth or body at all, they just make our temperature sensors fire. Perhaps most interesting is that if the nerves that detect heat fire intensively enough, the body will respond as if a real fire is happening, and inflammation (swelling and redness) happen for real.
So keep in mind that when we say something tastes good, we are really talking about our brain’s interpretation of hundreds of trillions of available flavors, and a vast degree of possible associations, textures, temperatures. Each bite is a universe of possibilities in a single moment for us to enjoy!