How Sour or How Sweet is Your Lemonade?
Summary
Introduction
Cooking is a fun and rewarding activity, allowing you to be cook and a scientist at the same time, experimenting with endless taste combinations! The five tastes humans can experience are: sweet, sour, salty, bitter and umami. But have you ever experienced some combinations that were delicious and others that were downright yucky? How do cooks come up with delicious recipes, and even more amazingly, how can they replicate the same exact flavors over and over again? Does science have anything to do with it? This activity will show how cooking and science can yield a delicious partnership.
Background
Food has taste because specific chemical particles found in the food activate taste buds in our mouth. Some tastes are created by one specific small particle (like the hydrogen ion, H+, for the sour taste) while other tastes are activated by several long complex particles (for instance, sucrose, sucralose and saccharin all induce a sweet taste). Cooks play around with the five tastes that humans can identify to create well-balanced delicious food. In this activity, you will experience how combining a sweet and sour taste creates an interesting experience.
Cooks use ingredients from nature, like lemons, which show a natural variability in the amount of taste-inducing particles they contain. One lemon might be more sour than the other. How can they reproduce a delicious taste over and over again while their ingredients show variations? The secret lies in the instruments they use. A more scientifically minded cook focuses on precision and prefers more exact instruments over the measuring spoons and cups that a typical cook uses. A scale is one example. It measures the mass of sugar, which is directly related to the number of sugar particles (or sweetness-inducing particles). Similarly, instead of adding a teaspoon of vinegar to balance the sweetness of a drink, a scientifically minded cook might direct you to add vinegar until you reach a specific pH. The pH of a liquid indicates how many hydrogen particles (or sour-inducing particles) are in the liquid. In other words, a pH meter can directly measure the number of sour-inducing particles in the fluid. This allows them to reproduce exactly the same taste-inducing food, over and over again.
Materials
- Three glasses
- Optional: Sticky notes or other ways to differentiate the glasses
- Water
- Measuring cup
- White crystal sugar
- Measuring spoons:
- A teaspoon
- A ¼ teaspoon
- Mixing and tasting spoons
- White wine vinegar; other types of vinegar will work, too, but might not provide an equally pleasant taste.
Preparation
- Differentiate your three glasses; this can be done with sticky notes reading ‘Sugar water’, ‘Sugar and vinegar water’, ‘Vinegar water’ or by placing different colored spoons in each glass.
Instructions
- Measure one cup of water and add it to the first glass. This will be the glass for sugar water.
- Add one teaspoon of sugar to the glass of water and stir until the sugar is dissolved. Taste the sugar-water solution. Does it taste sweet, pleasantly sweet or too sweet?
- Repeat the previous step four more times in the same glass, each time adding 1 teaspoon of sugar, mixing and tasting. After how many teaspoons did you find the sugar water pleasantly sweet?
- You have now added a total of five teaspoons of sugar. This is approximately twenty-five grams of sugar, or 4.4 1022 sugar particles. Do you find this amount of sugar in one cup of water unpleasantly sweet? Knowing 1 cup (about 240 ml) of soda has about twenty-five grams of sugar, why do you think most people find soda tasty, but find this sugar water yucky?
- Pour half of the sugar water from the first glass into a second glass. Be as precise as you can. This will be the glass for sugar and vinegar water. Set the leftover half cup of sugar water aside for later.
- You will now add vinegar to the sugar-water solution, a quarter teaspoon at a time. How much vinegar do you think you will need to add before the drink tastes nice, or do you think the sugar-water-vinegar solution will never taste nice?
- Add a quarter teaspoon of vinegar into the second glass, mix and taste the solution. How does it taste? Is it better than the pure sugar water?
- If your solution does not have a pleasing tasting yet, add another quarter teaspoon of vinegar, mix and taste again. Repeat this step until you get a pleasantly tasting solution, but remember to keep track of how much vinegar you added. Are you surprised about how quickly the sugar water changes taste as you add small amounts of vinegar?
- Set your sugar-vinegar solution aside and pour half a cup of water into the third glass. This will be your vinegar-water glass.
- Add the same amount of vinegar as you added to the second glass. This is probably one or two quarter teaspoons, maybe three. Mix the solution and taste. Is it a pleasant taste?
Extra: Knowing that each quarter teaspoon of vinegar contains about 5 1018 hydrogen particles (or sour-inducing particles), can you calculate how many sugar particles (or sweet-inducing particles) you needed to balance each sour-inducing particle? Why would we be so much more sensitive to the presence of sourness than to the presence of sweetness?
Extra: Taste is just one aspect of flavor. Smell, texture and even expectation all contribute to your experience of flavor. What can you add to your pleasantly tasting sugar-vinegar water to add more flavor without changing the concentration of sweet-producing and sour-producing agents? Some suggestions are lemon or orange rind, a slice of cucumber or even some food coloring.
Extra: Check the label of foods like tomato sauce, ketchup or lemonade, which all have a major sour component. Can you find a sweetening component in the ingredient list to balance the sour taste? You can do the same with recipes in a cookbook at home.
Extra: How exactly does a measuring cup or measuring spoon measure an amount of sugar? Try it out by loosely scooping out one cup of sugar and measuring its mass with a scale. Then, set aside this sugar and repeat the procedure again, and again. Do you get exactly the same number on your scale, or do you see small variations? Now repeat this, but press your sugar into the cup (or pack it tightly), and measure the mass of this amount of sugar. Repeat a few times to see how much variation you get this time. What other variations on scooping out a cup of sugar can you think of? Would the type of crystal sugar (e.g. coarse versus super fine) make a difference? Which method do you think is most exact in measuring an amount of sweetness-inducing particles, measuring its mass or measuring a volume?
Observations and Results
You probably found the sugar water very sweet, the vinegar water way too sour and the water with vinegar and sugar surprisingly tasty.
Our taste has actually evolved to help us detect nutritious foods and avoid foods that are harmful for us. Sweet, in general, indicates energy and vitamins, while sour can indicate unripe or rotting. The sweet and sour taste combination appears in many nutritious ripe fruits, like tomatoes and oranges.
Cooks are experts in creating pleasant-tasting recipes. They know the art of balancing out different tastes and how small amounts of sour-inducing particles can balance many more sweet-inducing particles. In your recipe, you probably added 2 or 3 ¼ teaspoons of vinegar, which corresponds to adding one sour-inducing particle for every 3,000 to 4,000 sugar particles to obtain a balanced taste.
A spoon or cup measures a volume of an ingredient, while a scale measures its mass. If you followed the ‘extra’ instructions, you probably realized how a tightly packed cup of sugar weighs quite a bit more than a loosely packed cup of sugar. Because sweetness-inducing particles have a specific mass, measuring the mass of the sugar will provide a more exact number of sugar particles than measuring a cup of sugar, which is why scientifically minded cooks often prefer a scale over a measuring cup.
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Additional Resources
- Pucker Up: Sweet and Sour Science, from Scientific American
- Cabbage Chemistry - Finding Acids and Bases, from Scientific American
- Science and Cooking: From Haute Cuisine to Soft Matter Science, from HarvardX on edX
- What are Tast Buds, from KidsHealth
