Quintessential to any high school biology class is the colourful illustration known as the tongue map. Adorning human anatomy textbooks for decades, this map neatly sections off the tongue into four segments, each with specialised taste receptors. The tip detects sweetness, the back bitterness and the two sides salty and sour tastes respectively. This simple concept of taste is not only taught in school, but is also the basis for special wine glasses designed to deliver a full flavor experience.
There’s one fatal flaw to this seemingly simple conception of taste: it is patently false. The first issue arises with the number of sections, and therefore tastes, that the map depicts. There are actually five known tastes, not four! The fifth taste is known as umami, which was first proposed in 1908 but not officially recognized until 1985. It is a savoury, ‘meaty’ taste that produces a mouthwatering and long-lasting sensation on the tongue.
How do these tastes arise? Well, your taste buds contain receptors that detect different chemicals, and these interactions result in brain signals that allow us to perceive taste. For example, umami is perceived when glutamate is detected by taste receptors. This is why lots of Asian dishes, containing monosodium glutamate (MSG), have the umami taste. Similarly, sweetness is experienced when sugars interact with your taste receptors, saltiness is due to sodium ions (sodium chloride is table salt) and sourness detects acidity. Scientists even suspect that there may be a sixth taste due to receptors that detect fatty molecules.
The tongue map arose from the incorrect notion that different taste receptors were localized to certain parts of the tongue. This misconception spread as a result of a psychologist misinterpreting a diagram in a German paper from 1901. In fact, this diagram was intended to show that there are tiny differences in how quickly different parts of the tongue detect a certain taste. This was taken out of context and restated as there being a difference in sensitivity.
Despite research showing that all parts of the tongue perceive all five of the basic tastes, this myth has persisted. In reality, we still have lots to learn about taste receptors – it was only in 2007 that we figured out exactly which receptors were responsible for bitter, sweet and umami tastes. A recent study in 2006 also found that receptors for each of the different tastes are located in distinct cells – that is, there are cells containing only sweet receptors, and other cells containing only sour receptors, and so on. But these cells are spread evenly across the tongue.
So you can forget about the fictitious tongue map and expensive flavour-administering wine glasses, and instead focus on just enjoying the taste sensation of your meal of choice – whether it be sweet, sour, bitter, salty or umami!