How Do We Taste What We Eat?
Taste is one of those senses that we take for granted - until we get a cold. Then, it seems that we can't taste anything. How we perceive taste is a complicated chemical process, and, it is closely linked to the sense of smell. Further complicating the issue is the idea of flavor. Taste is the information that our taste buds can tell us about what we eat. It is only one aspect of the flavor of a food. Flavor is a composite profile of a food based on its smell, mouth feel and temperature as well as its taste.
Remember the map of the tongue that your seventh grade science teacher passed out to you in class? Remember the areas for sensing sweet, salty, sour and bitter? Well, forget that. It turns out that the entire tongue, upper palate and even the inside of the cheeks have taste buds that can determine all of these flavors. While it is true that some areas of the tongue are more sensitive to certain tastes than others, the "tongue map" falsely leads people to believe that there is a strict differentiation among the different receptors, and this just is not the case.
What About Those Bumps?
Many people think that the bumps on the tongue are the taste buds. This is incorrect. Taste buds exist in groups of 50-250 inside the little "bumps" on our tongues, called papillae. There are four different types of papillae, two concentrated towards the front half of the mouth and two towards the back of the mouth. These four types of papillae do not indicate four discrete areas of taste, however. Although perhaps more sensitive to one taste over others, all taste buds can detect all basic tastes.
The tongue can detect five tastes: sweet, salty, sour, bitter and umami (savory). While you are probably familiar with the first four, umami is a taste that is relatively new to the Western palate, although the Japanese have known about it for decades. Umami is based on the detection of glutamate. Many foods, including the seaweed that some Japanese broths are based on, naturally contain glutamate. You have probably heard of "MSGmonosodium glutamate" is the lab-derived chemical that enhances tastes"”it makes things taste more like what they are; while umami is a taste that is hard to define, it is sometimes described as "meaty".
What Happens When We Taste?
Here is what happens when we taste. First, we must smell - whether as a conscious deep sniff before eating, or just as scents waft up our nasal passages. Smell triggers an increase in saliva production in the mouth and a low-level increase in digestive acid production in the stomach. This prepares us to taste and digest our food. To taste anything at all, foods must be dissolved. Try putting a bit of food on your dry tongue. You won't taste a thing.
Once food enters the mouth, its chemical components find their way to the taste buds. Some taste buds react most to the presence of sodium ions, and you will taste "salt". Others react mostly to sugars, acids, alkaloids or glutamates in the food resulting in tasting "sweet", "sour", "bitter", or "umami".
Studies show that humans are hard-wired to like certain tastes and to reject others, most likely for survival. Sour and bitter tastes can indicate food that is bad, under-ripe or even poisonous. Sweet, salty and savory tastes indicate "good" foods. A sweet taste indicates foods that can give us energy"”infants crave sweet foods, and lactose in milk is sweet. A salty taste indicates foods that can help us replace electrolytes lost through sweat or urination, and savory tastes can lead us to foods containing amino acids that the body needs.
Taste Versus Smell
Humans only recognize five tastes, but we can recognize thousands of smells. It is the way the brain puts together the tastes with the smells, temperature and mouth feel that creates our perception of "flavor". As much as 85% of the perception of taste comes from the sense of smell. Smells travel to the brain in two ways, up through the nostrils as you bring food to your mouth, and again through the "back door" once food is in the mouth, as some smells make their way up to the scent receptors through the pharynx.
While vanilla ice cream and apple pie both register as "sweet" on the tongue, their flavors are different because their smell, mouth feel and temperature are being processed at the same time as the tastes. The end result is the flavor of ice cream versus the flavor of apple pie.
When "smell" is taken out of the equation and mouth feel and temperature are similar, it is no wonder that an apple and an onion "taste" the same.