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Flavour Perception

In this activity, students learn that our perception of flavours can be affected by our sense of sight. What we see influences what we taste!

Distinguishing tastes

In a world of lime-flavoured tortilla chips, 100s of different jellybeans and countless flavors of ice cream, our sense of taste might seem to exist purely for pleasure. Instead, the ability to distinguish bitter from sweet does far more than help us choose between light and dark chocolates.

Sweetness is a signal that what we are eating will give us energy, while bitterness can warn that we may be about to swallow something toxic. In our primordial past, long before nutritional labelling, using such cues was essential to survival, as it still is for animals living in the wild.

Identifying tastes is the brain's way of telling you about what is going into your mouth, and in some cases, keeping you safe. One example is drinking milk that has gone off and turned sour. When the milk hits the taste buds, they send nerve impulses to the brain: "Milk coming in—and it tastes weird.” Once the brain unscrambles the nerve impulses, it recognizes the taste as a potentially dangerous one, and you know not to drink the milk.

Taste buds

How do you know how something tastes? Each taste bud is made up of gustatory cells (taste-sensing cells), which have sensitive, microscopic hairs called microvilli. Those tiny hairs send messages to the brain, which interprets the signals and identifies the taste for you.

The average person has about 10,000 taste buds and they are replaced approximately every 2 weeks. As a person ages, some of those taste cells are not replaced. An older person may only have 5,000 working taste buds. That is why certain foods may taste stronger to children than they do to adults. 

Tricking taste buds

Some things can make your taste bud receptors less sensitive, such as cold foods or drinks. An ice pop made from your favorite juice does not taste as sweet as plain juice. If you suck on an ice cube before you eat a food you dislike, you do not notice the bad taste. The way food is prepared also makes it taste different: compare raisins and grapes; boiled, scrambled and poached eggs; potatoes that have been mashed, baked, roasted, boiled and fries.

If food has a different colour than normal, the brain will get mixed signals from the mouth and the eyes. The food will seem to taste different. In fact, food companies add colour to food to influence what it tastes like. People like to see foods in colours that they expect. Without colour additives, colas would not be brown, margarine and cheese would not be yellow or orange, and mint ice cream would not be green. Colour additives are recognized as an important part of practically all foods we eat.

Objectives

  • Outline how the body’s taste buds detect different tastes.

  • Identify and explore the five basic senses.

  • Explore the connection between different senses.

Materials

  • Per Class or Group:
    different samples of food colouring
    drinks that are clear or pale coloured (e.g. club soda, tonic water, strained white lemonade, apple juice, tap water)
    large glasses or jugs
    paper cups
    eye droppers (optional)
    paper and pens

Key Questions

  • Why is blue food weird?
  • Why could the colour of a food item affect its taste?
  • How could you improve your sense of taste for this activity? (Close your eyes!)

What To Do

Set up

  1. Pour each liquid for testing into a jug.
  2. Add a couple of drops of food colouring to each jug to dye the liquid an uncharacteristic colour. For example, lemonade can be dyed purple to look like grape juice.

Activity

  1. Get the students to stick out their tongues and look at their neighbour.
  2. Explain that the bumps they see on the tongue are called papillae and most of them contain taste buds. Taste buds have very sensitive microscopic hairs called microvilli. Those tiny hairs send messages to the brain about how something tastes, so you know if it is sweet, sour, bitter, salty, or savoury.

Optional: Further explain that when you chew food, the food releases chemicals that immediately travel up into your nose. These chemicals trigger the olfactory receptors inside the nose which also send signals to the brain. The olfactory receptors and the taste buds work together to create the true flavor of the food you are eating.

  1. Show the students the jugs of coloured liquids and tell them to taste each one in turn and guess the flavour of the drink. This can be done by dropping samples onto their tongues with the eye droppers.
  2. Reveal the identities of the coloured drinks and see how many students guessed correctly. Explain that colour association can alter basic taste sensations and determine the acceptability of food. People naturally prefer red, yellow and brown food like ripened fruit and vegetables. Experiments have shown that people dislike blue coloured food. Further tests have shown that people also have difficulties tasting food which is “wrong” coloured like green coloured strawberry yogurt. If food has a different colour than normal, the brain will get mixed signals from the mouth and the eyes. The food will seem to taste different.

Extensions

  • Use the same liquid, for example soda water, in separate jugs and add increasing amounts of sugar (or salt). Dye each jug a different colour and see if the students can guess the order of sweetness (or saltiness).

Other Resources

Science World Bonus | Why is Cheddar Cheese Orange?