Sweet chemistry

This Valentine's Day, while you're tearing open the wrappers on red and pink lollipops and crunching colorful candy hearts, take a minute to think about how those sweet treats are made. It might surprise you!

Would you believe that all candy, from cotton candy to fudge to peanut brittle, starts out as a plant? But not just any plant - a plant that contains sugar, like the sugar cane or the sugar beet.

When sugar cane and sugar beets are harvested, they go to a mill, where the plants are cut into shreds and then huge rollers press out what's called "raw sugar." This is then sent to a refinery, where it's made into different types of edible sugar like granulated sugar, brown sugar, and powdered sugar.

"Although there are many different types of sugar that you can use for baking," says Lisa Futterman, "plain old granulated sugar works best for most types of candy." Ms. Futterman is director of the Chopping Block Cooking School in Chicago.

But turning those tiny sugar granules into a creamy, chewy, or crunchy candy isn't as easy as it may seem. In fact, Futterman says it can be tricky. Even dangerous. "Cooking sugar to make candy requires an intense amount of heat," she says. Most recipes require temperatures of between 240 and 310 degrees F. To give you an idea of how hot that is, consider this: Water boils at 212 degrees F.

But let's back up. Making candy is tricky because you can't just cook sugar by putting it in a pot on the stove, says Darrin Aoyama. "Hot sugar is very difficult to control because it gets hot really fast," says the pastry chef at the River Oaks Country Club in Houston. He's also on the United States' 2004 Culinary Olympics Team that competes this October in Germany. To control the heating process, chefs mix the sugar with water. Water helps slow down the temperature changes in the sugar.

That's because water never gets hotter than 212 degrees F. At that temperature, it starts to boil and then to evaporate. When you heat sugar and water to 212 degrees, the water in the solution will cause it to boil. As the water boils away, the sugar and water solution gets hotter. In fact, the temperature of the solution tells you what percentage of water is left.

Different types of candy require different concentrations of sugar. This is called "saturation." When a solution is "saturated," it holds as much sugar as it can at a certain temperature - no more sugar will dissolve in it. In fact, to make many types of candy, there must be so much sugar in the water that it isn't just saturated, it's "supersaturated."

Here's where you have to be extra careful when cooking: The more concentrated the sugar solution, the less stable are the sugar molecules. Adding just a speck of dust, or changing the temperature ever so slightly can cause the solution to crystallize early. At lightning speed, your smooth syrup will turn into a grainy glop.

It is also important that you carefully watch to see how hot this solution gets. That's because how hot it gets determines what kind of candy you make. "The temperature of sugar solutions jumps quickly," Futterman says, "so you have to watch it very closely." It's critical to use a candy thermometer as your guide, but "it's also cool to do the 'cold water candy test'."

Here's how it works: Say you are making fudge. Most fudge recipes direct you to heat your sugar solution to about 235 degrees F. on a candy thermometer. (Make sure that when you're reading the thermometer it's not touching the bottom of the pot, Futterman says, or you could get an inaccurate reading.)

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