Have you ever tasted a lemon? To most people a lemon tastes very bitter or sour. So how do you get the lemon taste in foods without the bitter taste? The easiest approach is to simply add sugar. Sugar covers up the bitter acid taste of lemons by neutralizing the bitter acid taste. For example try lemonade with and without sugar, which tastes better?
Another ingredient added to foods for a better taste is salt. This ingredient is added to many processed foods to cover up the bitter acid taste of preservatives. Salt also covers up the sweet taste of sugar; so salt is added to make real sweet foods taste less sweet. For the opposite effect, sugar is sometimes added to tone down the salty flavor of processed foods.
Basically, real salty processed foods probably contain many preservatives. If too much salt is necessary to cover the preservative bitter taste, then sugar is added to make the food taste less salty. This brings into question the healthy aspect of processed foods.
Tonic water contains low levels of quinine, which has a bitter acid taste. Quinine was added to tonic water in the past in large amounts to help people prevent contracting malaria. Today's tonic water only contains a small amount of quinine for flavor. Reading the ingredient labels of tonic water helps determine the amount of quinine in the tonic water.
An interesting way to test tonic water for quinine is to hold a black light (UV) next to a bottle of tonic water – ff it glows blue, then it contains quinine. See the picture at the bottom of this article for an example.
Tonic Water Cover Up Investigation
This investigation will determine the effects of adding salt to tonic water to decrease the acid bitter taste of quinine in tonic water.
Materials – marker, masking tape, four drinking glasses, stirring stick, 16 ounces of tonic water with quinine for each station, salt, note paper and pencil/pen
Procedures – students do the following:
- Label the four glasses with numbers 1 through 4 and fill each glass with 4 ounces of tonic water.
- Put a pinch of salt in glass 2 and stir.
- Put 1/2 teaspoon of salt in glass 3 and stir.
- Put 1 teaspoon of salt in glass 4 and stir.
- Take a sip of tonic water in glass 1.
- Record the bitterness of the tonic water in glass 1 using a scale of 1 to 5, with 5 being very bitter and 1 being not very bitter.
- Take a sip of tonic water in glass 2 and record the bitterness level using the same scale.
- Take a sip of tonic water in glass 3 and record the bitterness level using the same scale.
- Take a sip of tonic water in glass 4 and record the bitterness level using the same scale.
- Students create a graph of their investigation, labeling the dependent and independent variables.
- Write a short story of the investigation which includes their hypothesis, variables, findings, and conclusion.
Questions to Ask Students –
- What happened to the taste of the tonic water in each of the four glasses?
- What evidence do they have to support their answer?
- 20 Questions to Ask Students in Science Projects provides additional ideas for questions to ask students regarding this investigation.
Extensions –
- Substitute sugar for the salt and conduct the investigation again.
- Students conduct the investigation using stations, for example: one station uses table salt, one station uses sea salt, one station uses processed sugar, and one station uses a sugar substitute. Have students cycle through each investigation station and a computer station with access to the Internet for research. See Web-Based Science Inquiry Learning Centers for procedures regarding setting up web-based inquiry learning centers.
Student Resources –
- Taste Buds – provides an overview of the purpose and use of tastes buds on the tongue.
- Your Tongue – provides a guide of the location of all taste buds on the tongue.
Determining how much sugar or salt to add in when cooking food is part of the chemistry of cooking. Learning how processed food manufacturers cover up undesirable tastes in food to make food tasty provides students with the opportunity to make a better informed decision about their diet.
David R. Wetzel - Dr. David Wetzel's experience includes more than 25 years in continuing, adult, and teacher education.
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