Sensory Science: Testing Taste Thresholds
During the holidays, we often find ourselves surrounded by a wide variety of taste sensations. Have you ever wondered how well we sense different tastes? People are generally able to discern five basic tastes: sweet, umami (also known as savory), salty, sour and bitter. Is it easier to detect some of these flavors at low concentrations compared to others? In this science activity, you (and possibly your friends and/or family) will find out by exploring your taste thresholds for sweetness, saltiness and sourness. Get ready to find out how low you can go!
Our sensory system for taste is remarkably sensitive. Not only can we detect substances at extremely low concentrations, we can also differentiate between molecular compounds that are closely related. For example, for some molecules we can distinguish between different stereoisomers, which are molecules that are made of exactly the same components, but are mirror images of one another. The artificial sweetener aspartame is an example of this – it tastes sweet to us, but its stereoisomer does not.
This amazing sensitivity is made possible by our taste buds. Taste buds, located on small bumps on the tongue called fungiform papillae, are each made up of about 50 to 150 taste receptor cells. On the surface of these cells are receptors that bind to small molecules related to flavor. Through sensory nerves, the receptors relay the taste sensation information to the brain. This entire process allows us to discern five basic tastes.
- Measuring spoons
- Water, preferably distilled
- 12 paper or plastic cups
- Permanent marker
- Kitchen scale or measuring spoons
- Granulated sugar, or sucrose
- Table salt
- Cotton swabs
- Paper towels
- Piece of paper and pen or pencil (optional)
- Taste test volunteers (optional)
- Pour six tablespoons (Tbsp.) of distilled water into a paper or plastic cup. Add 10 grams of sugar (or about 2 ½ teaspoons [tsp.]) and stir until the sugar is dissolved. This gives you an approximate 10% sugar solution. Label the cup.
- Pour two tsp. of the 10% sugar solution into a new cup. Add six Tbsp. of water to it and stir. This gives you a 1% sugar solution. Label the cup.
- Repeat this dilution process (diluting two tsp. of the previous solution in a new cup with six Tbsp. of water) to make 0.1% and 0.01% sugar solutions. These are called serial dilutions. Be sure to label the two new cups. What do you think is the lowest concentration you’ll be able to taste the sugar in?
- Repeat these steps (using clean utensils) to create salt solutions that have concentrations of 10%, 1%, 0.1% and 0.01%. Label the cups. For 10 grams of salt, you can use 1 ¾ tsp. of salt. What do you think is the lowest concentration you’ll taste the salt in?
- Again repeat the steps (using clean utensils) to create vinegar solutions that have concentrations of 10%, 1%, 0.1% and 0.01%. Label the cups. Use two tsp. of vinegar initially. What is the lowest concentration you think you’ll taste the sour vinegar in?
- Rinse your mouth with plain water and wipe your tongue dry with a clean paper towel. Dip a clean cotton swab into the 10% sugar solution and smear it all around your tongue. Can you taste the sweetness?
- Repeat the previous step to test the 1%, 0.1% and 0.01% sugar solutions, rinsing your mouth and wiping your tongue before testing each solution. Which solution is the lowest concentration at which you can still taste the sweetness? This is your approximate taste threshold for sugar. You can write this down to remember later.
- Rinse your mouth with plain water and wipe your tongue dry with a clean paper towel. Dip a clean cotton swab into the 10% salt solution and smear it all around your tongue. Can you taste the saltiness?
- Repeat the previous step to test the 1%, 0.1%, and 0.01% salt solutions. Which solution is the lowest concentration at which you can still taste the saltiness? This is your approximate taste threshold for salt. You can write this down.
- Rinse your mouth with plain water and wipe your tongue dry with a clean paper towel. Dip a clean cotton swab into the 10% vinegar solution and smear it all around your tongue. Can you taste the sourness? Repeat this process to test the 1%, 0.1% and 0.01% vinegar solutions. Which solution is the lowest concentration at which you can still taste the sourness? This is your approximate taste threshold for vinegar. You can write this down.
- Were your taste thresholds (the lowest concentration at which you could still taste the flavor) the same for all three tastes, or did you have lower thresholds for some of them? Did the solutions that were 10-fold more concentrated taste 10-times stronger?
Extra: Try repeating this activity using several volunteers. Compare your results. Do some people generally have lower thresholds than other people? Is there variation in which taste has the lowest threshold for people in the group?
Extra: Recruit several volunteers in different age groups to take this threshold of taste test. Does taste threshold change predictably with age?
Extra: In this activity you used 10-fold serial dilutions to roughly establish your threshold of taste. Design a test to determine your threshold with higher precision. What exactly is your taste threshold for sugar, salt and vinegar?
Observations and Results
Could you taste all of the 10% solutions, but none of the 0.01% solutions? Did the sugar solutions have the highest threshold, meaning you could only taste it in the more concentrated solutions, compared to the salt and vinegar solutions, which had lower thresholds?
For the sugar, salt and vinegar solutions, the 10% solutions should be detectable by nearly everyone who tries the test, while almost no one should be able to detect the 0.01% solutions because the concentrations are too low. The different basic tastes (sweet, salty and sour) have different thresholds, or concentration levels, at which they can be detected. In other words, it’s easier to detect some flavors at low concentrations compared to others flavors. Taste thresholds can vary from person to person. You may have seen that the sugar solutions were harder to taste at lower concentrations compared to the salt and vinegar solutions. In other words, the sugar solutions may have had a relatively high taste threshold compared to the salt and vinegar solutions. You may have also seen that the vinegar solutions had a lower threshold compared to the salt solutions (meaning the vinegar was easier to taste at lower concentrations), but this difference can be minor and may require testing many individuals to see a clear trend.