How Warm Is Sweet Enough? - Scientific American

Key Concepts
Human biology
Senses
Taste
Smell
Food Science

Introduction
Have you ever tasted a piece of warm apple pie or a cup of hot chocolate milk—and then had them after they cooled? Maybe you even prefer to have these treats at room temperature. Why is this? Can flavor change even when you are not adding ingredients? Try this activity, and discover how temperature influences flavor!

Background
Our experience with flavor starts in our mouth. There the particles in food that are responsible for taste activate our taste buds. When these taste buds are triggered they send a signal to our brain, and we perceive a particular flavor. Humans have thousands of taste buds; they are mainly located on the tip and upper parts of the tongue. They help to distinguish at least five basic tastes: sweet, salty, savory (umami), bitter and sour—and provide information on the intensity of each of these.

Our experience with flavor does not end in the mouth. It is also influenced by our sense of smell. Food also releases scent particles. When these particles float into our nose they activate our smell receptors. These receptors send a signal to our brain, and we perceive a particular smell. Humans have several million specialized smell receptors; they are mainly located in our nasal cavity. When food is heated it releases a burst of these particles. That is why you can easily smell the delicious pie baking in the oven or a hearty soup cooking on the stove.

Our brain combines the signals from our taste buds with those received from our smell receptors to produce the broad sensation of flavor that we are familiar with. Scientists have found that taste buds work more efficiently at warmer temperatures than at colder ones. Does that make us perceive the flavor of warm food more intensely? Try this activity to find out!

Materials

• Ice cream
• Two small bowls
• Spoon
• Two pieces of milk chocolate
• Freezer
• Glass of water
• Volunteers (optional)
• Milk or chocolate milk (optional)
• Two mugs (optional)
• Microwave or stovetop (optional)
• A bitter- or sour-tasting food or drink, such as unsweetened tea, lemonade and so on (optional)

Preparation

• At least half an hour before you start the activity place one piece of milk chocolate in the freezer. Leave the other piece out at room temperature.
• Scoop a small amount of ice cream into a bowl, and leave it out at room temperature. Return the rest of the ice cream to the freezer.
• Do not consume sugary or strongly flavored food in the half hour before you start the activity.

Procedure

• Remove the piece of chocolate from the freezer. Break off a small piece, and leave the rest in the freezer.
• Place the small, cold piece on your tongue. Close your mouth and concentrate on the flavor. What does the chocolate taste like?
• Let the chocolate melt in your mouth. Does the flavor change as the chocolate melts? When is the flavor of chocolate the strongest?
• Rinse your mouth with water.
• Break off a small piece of the room-temperature chocolate and repeat the previous three steps with this piece. Is the initial flavor of this chocolate stronger compared with the initial taste of the ice-cold chocolate? Does the flavor change as this piece melts?
• Take more of the cold chocolate from the freezer, and compare the smell of the cold chocolate with that of the room-temperature chocolate. Does one smell more strongly than the other? Could the difference in smell account for the difference in flavor?
• Remove the ice cream from the freezer and scoop a small amount into a bowl.
• Compare the smell of the frozen ice cream with that of the room-temperature ice cream. Which ice cream produces the strongest smell? Is there a perceivable difference?
• Place a spoonful of frozen ice cream in your mouth. Close your mouth and concentrate on the flavor. What is the flavor like? Is it too sweet, just right or not sweet enough?
• Let the ice cream melt in your mouth. Does the flavor change as the ice cream melts? At what point do you experience the strongest flavor?
• Rinse your mouth with water.
• Taste the room-temperature ice cream. How is the flavor different from that of the frozen ice cream? Does it taste just as good? Why or why not?
• Extra: Ask volunteers to perform the same tests that you just did. Do they experience similar changes in perceived flavor that you did? Why do you think this happens?
• Extra: Taste more of the melted ice cream. Then without rinsing your mouth taste the frozen ice cream again. Does the frozen ice cream taste as sweet as it did the first time you tasted it? Did eating something very sweet first change your perception of the next item you ate?
• Extra: This activity compared ice-cold food with room-temperature food. Compare room-temperature milk or chocolate milk with warm versions. Be careful not to consume scorching-hot drinks! Is the smell of one stronger than that of the other? Does one taste sweeter than the other?
• Extra: This activity tests sweet food. Test if the same conclusions are valid for bitter or sour drinks or foods.

Observations and Results
Did you notice the flavor of food changes as it undergoes a change in temperature?

Our sense of taste is more sensitive to warm food than to cold food. That is why the frozen ice cream probably tasted just sweet enough, whereas the melted version probably tasted much too sweet. Similarly the frozen chocolate probably had very little taste until it warmed up in your mouth. The intensity of the taste increased as the food warmed up. The smell might have become stronger, but probably not drastically. If you tried the activity with food that had been heated, such as warm milk, you probably noticed that the intensity of the smell increased along with the intensity of the flavor.

Foods are prepared to be eaten at a certain temperature. When people prepare meals they aim for the temperature the food will be served at that gives the desired flavor. In addition to flavor, however, people also think about the texture of food. So if the flavor of your pepperoni pizza is too strong, or if you want your ice-cream to taste a little sweeter, cooling it or heating it might not be the ideal solution.

More to Explore
Some Foods Taste Different Hot or Cold, from Live Science
The Nose Knows Smell but How About Taste? from Science Buddies
Sensory Science: Testing Taste Thresholds, from Scientific American
Battle of the Senses: Taste Versus Smell, from Science Buddies
Tricky Taste Test: Do You Taste with Your Eyes? from Scientific American
STEM Activities for Kids, from Science Buddies

This activity brought to you in partnership with Science Buddies

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