From Scientific American:
Have you ever wondered why some foods or drinks taste sour whereas others do not? You might know that your tongue is picking up all kinds of flavors, including salty, sweet, bitter and sour. But what makes something taste sour? The sour taste is actually influenced by the pH and acids present in foods. In this activity you will find out how sour different foods are by testing foods and drinks for the presence of acids with baking soda. What do you think is the sourest food you can find in your kitchen?
Taste is detected by taste buds that line the tongue and other parts of the mouth. The human tongue has an average of 10,000 individual taste buds! Inside each taste bud are as many as 100 receptor cells. Each receptor is best at sensing a single sensation and sends signals about it to the brain, which then identifies sweet, salty, bitter, sour or umami. Different receptors are triggered by different chemical compounds (or molecules) present in the food. The sour taste receptors are triggered by acids, or more specifically hydrogen ions (H+), and therefore are the tongue’s acid detectors.
What does it mean for something to be acidic or basic? It all has to do with ions. In water (H2O) a small number of the molecules split up to form hydrogen ions (H+) and hydroxide ions (OH−). Pure water and solutions that have an equal number of hydrogen ions and hydroxide ions are neutral—that is, they are neither acidic nor basic. An acid is a substance that donates hydrogen ions. Because of this, in an acidic solution there are more hydrogen ions than hydroxide ions. This means the more acidic a food is, the more hydrogen ions are available to trigger the sour taste receptors. A base …