92 The Science of Lemonade-Low

The Science of Lemonade FOCUS Question How does the balance of chemicals in lemonade affect how it tastes?

Tasty Chemistry Gulp, gulp, gulp... aaah! You just drank an ice-cold glass of lemonade. Alone, lemons are sour enough to make your face pucker. But lemonade is just the right mixture of tangy and sweet. What makes this lemony liquid so yummy? That delicious taste comes from the chemicals in the basic ingredients of fresh lemonade: water, lemons, and sugar. You might drink premixed lemonade from a carton or mix water with a powder or frozen concentrate. Those types of lemonade may taste a little different because of other added ingredients. But the final product is still a combination of chemicals that gives your tongue a treat.

That glass of lemonade tasted so good you make another one. Following your recipe, you measure the right amounts of water, lemon juice, and sugar. You then combine the liquids and solids in a glass. You stir a few times and take a drink. Wait! That's not lemonade! The sugar has not dissolved and has mostly settled to the bottom. You have made a heterogeneous (HEH-tur-o-JEE-nee-us) mixture, which means the parts are still separate. Stir until the sugar dissolves and the clear water turns yellow. Now you have stirred up a lemony, sweet solution. All the ingredients mixed together evenly to make a homogeneous (HO-muh-GEE-nee-us) mixture. Your last sip will taste the same as your first. Also, it would be difficult to separate the ingredients. This is lemonade!

What's Happening in the Glass? Your three ingredients form a well-mixed solution because of the attraction between their atoms. Atoms that have negative charges connect, or bond, with atoms that have positive charges. A water molecule has two hydrogen atoms (slight positive charge) and one oxygen atom (slight negative charge). Sugar, or sucrose, also has hydrogen and oxygen atoms with slightly positive and negative charges. When you add sugar to water, the atoms in the two substances are attracted to each other. The natural citric acid from the lemon juice has atoms with positive charges that are attracted to the negative charges in the water molecules. All these bonded atoms form a sweet-tasting solution.

Sweet over Sour The tangy, sweet taste of lemonade is due to the citric acid and the sucrose at work. In water, sucrose (sugar) begins to break down into two different molecules, glucose and fructose. Citric acid molecules from the lemon juice speed up this process. The newly released fructose is sweeter than sucrose, so now the lemonade tastes sweeter. Sometimes it takes a few tries to get the right balance of sweet and sour when you're making lemonade. Sucrose is a good flavor suppressor. It overpowers other flavors, especially the sourness of citric acid. Sucrose also resists being overpowered by other flavors It is a good idea to follow a recipe closely so you don't make lemonade that's too sweet.

Taste, the Tongue, and the Brain Remember that first sip of lemonade? You tasted it with your tongue, but your brain told you what flavor you were sensing. Inside your mouth are about five to ten thousand taste buds that detect chemicals. The more taste buds you have, the more sensitive you are to tastes, especially bitter tastes. Most of your taste buds are located on the bumps, or papillae (puh-PIL-ee), that cover your tongue. Each taste bud has special detectors for five different types of tastes: sweet, sour, salty, bitter, and umami. (Umami is the taste that is found in foods such as meat, tomatoes, and soy sauce.) Fact or Fiction? People once believed that the tongue had specific areas for each taste. But in fact, all parts of the tongue can sense many different tastes.