Things You'll Need
Pan of boiling water
Candy sugar solution
A candy thermometer measures the sugar solution used in cooking candy. There are three kinds of candy thermometers. The dial thermometer has a round face with a needle that points to the temperature. The glass thermometer contains liquid that rises as the solution grows hotter. It looks like a weather thermometer. The digital thermometer, with a digital readout, is the most accurate of the three. All of the thermometers will measure temperatures between 100 and 400 degrees Fahrenheit.
Submerge the end of the candy thermometer in boiling water to test for accuracy. A temperature of 212 degrees at sea level is accurate. If it varies, you will need to compensate for the difference as you cook.
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Adjust for the difference while you are cooking candy. If the accuracy test shows a temperature of 214 degrees, you have a difference of 2 degrees. If the candy recipe says it needs to reach a temperature of 250 degrees, the correct temperature adjustment is 250 degrees plus 2, or 252 degrees.
Make adjustments, if needed, for high-altitude candy cooking. Subtract 2 degrees for every 1,000 feet you live above sea level. If you live 2,000 feet above sea level and the candy recipe calls for a temperature of 250 degrees, subtract 4 degrees from the 250 degrees, and cook the candy to 246 degrees.
Attach the candy thermometer to the side of the pan cooking the candy. Check the candy thermometer often so you know when it reaches the right temperature. If the tip of the thermometer rests on the bottom of the pan, you will get a false reading.
The different stages of cooking candy are marked on some candy thermometers. The digital thermometer is the easiest to read. It's hard to see the temperature reading on a glass candy thermometer when it's attached to the pan.
Be careful. The sugar solution of candy is very hot and it can burn before you can remove it from your skin.