Finding Your Threshold of Taste, 2015

 

Introduction

 

     The objective of this experiment is to determine the lowest concentration of a substance dissolved in water which can still be tasted; the substances that will be used are sugar, salt, and vinegar.  Your threshold would be the lowest concentration value or percentage that you can still taste the solution.  In other words, if your threshold level is low (i.e. .001%) then you would be very sensitive to that substance (or you could taste that substance at very low concentrations).  If your threshold level is high (i.e. 10%) then you would not be very sensitive to that substance (or you would only be able to taste that substance at high concentrations). When you were very young, your threshold was low due to the fact that your taste buds where newly developing and very sensitive; there’s an opposite effect when you’re older, typically the elderly lose their taste buds.

 

Apparatii:

Stock Table: sugar (sucrose) salt (sodium chloride) vinegar (acetic acid) water (tap) paper towels 25 mL graduated cylinder (clean) * (for measuring 10 mL of vinegar)                                   spoon(s) electronic balance(s)

Student Table: (1) ruler (metric) (1) stirring rod (plastic) (5) standard coffee cups* (3) Dixie cups* for 2 students (1) pen/fine marker (30) cotton swabs for 2 students   * pre-measured 90mls and 10mls   Note: (4) more Dixie cups will be needed per student later

Procedure:

 

 

Making the Measuring Cups and the Dilutions: (see diagram of dilution handout)

 

  1. Make “pre-measured device cups” by doing the following:

       - use a metric ruler and measure 4 cm from the bottom of the “coffee” cups and then mark a line inside and outside the cups. The line will represent a 90 ml measurement.

       - use a metric ruler and measure 1 cm from the bottom of 1 “Dixie” cup and then mark a line inside and outside the cup. The line will represent a 10 ml measurement.

       - the other 2 “Dixie” cups will be used as “rinsing” cups: Label one cup with your name and the word “Rinsing Cup” with a pen/marker; do the same for your partner with the other cup; but with their name.

    

  2. Measure out 90 mL of water by placing it into each of your measured “coffee” cups.

 

  3. Label each “coffee” cup accordingly: 10%, 1%, .1%, .01%, and .001%

 

  4. Measure 10 grams of sugar using the electronic balance (as per instructed) and add the 10 grams of sugar to the “coffee” cup  marked 10%. Use a clean stirring rod, mix the solution well (try to dissolve completely). This will give you a 10% sugar solution.

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  5. Measure out 10 mL of the 10% sugar solution by pouring it into your measured “Dixie” cup.

 

  6. Place the 10 mL of the 10% sugar solution from your “Dixie” cup into the “coffee” cup marked 1%.  This will give you a solution of 1% sugar solution.

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  7. Measure out 10 mL of the 1% sugar solution by pouring it into your measured “Dixie” cup.

 

  8. Place the 10 mL of the 1% sugar solution from your “Dixie” cup into the “coffee” cup marked .1%.  This will give you a solution of .1% sugar solution.

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  9. Measure out 10 mL of the .1% sugar solution by pouring it into your pre-measured “Dixie” cup.

 

10. Place the 10 mL of the .1% sugar solution from your “Dixie” cup into the “coffee” cup marked .01%.  This will give you a solution of .01% sugar solution.

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11. Measure out 10 mL of the .01% sugar solution by pouring it into your pre-measured “Dixie” cup.

 

12. Place the 10 mL of the .01% sugar solution from your “Dixie” cup into the “coffee” cup marked .001%. This will give you a solution of .001% sugar solution.

 

13. You now should have 5 “coffee cups” labeled accordingly.

 

14. Arrange each “coffee” cup from the smallest concentration to the highest from left to right.

 

 

Tasting Procedure:

 

Sweetness

 

15. Gather 5 cotton swabs and some paper towel; also, fill your “rinsing” Dixie cup with water

 

16. Place each cotton swab into each “coffee” cup.

 

17. Have the one being tested on rinse their mouth with the “rinsing” Dixie cup and have them wipe their tongue dry with the clean paper towel.

     

      Note: Don’t put your tongue back into your mouth.

 

18. Have the other partner smear, coat, paint the .001% solution all around the tongue of the other partner.

 

      Then ask the following question at which time, place the appropriate mark in the Table on the data sheet:

 

      “Can you taste the substance being tested”?

     

      If “Yes”, place a (+) in the data chart in accordance to the threshold value / percentage

      If “Unsure”, place a (/) in the data chart in accordance to the threshold value / percentage

      If “No”, place a (-) in the data chart in accordance to the threshold value / percentage

       

19. Keep on doing the experiment for .01%, .1%, 1%, and 10% solutions (steps 15-18) even if you have reached your threshold level.

 

20.  You will switch partners and re-perform this test. (Note: Use the table on the data sheet to record your threshold level and your partner’s levels  (see Student  #1 and Student #2):

 

Note: The lowest concentration at which you can still taste is your approximate taste threshold for that solution.

 

Continuing the Taste Procedure: 

 

 

 

Salty and Sour**

 

21. Rinse the “coffee” cups “only” (pour any solution into the sink and “do not” use soap).

 

22. Throw away the “Dixie” cups that had previous solutions and obtain 2 more and re-mark 10 mls (the “rinsing” Dixie cup can stay with you)

 

23. Rinse the stirring rod.

 

24. Repeat the experiment with salt (salty) and then with vinegar (sour) **.

 

**   Note: To make a 10% solution of vinegar, use 10 mL of vinegar (measured from the cleaned graduated cylinder) and add it to your 90 mL of water in your 10% marked “coffee” cup.

 

25. Clean and return all materials.