Testing your thermometer is one of the most important steps in candy making to ensure success in the recipe. The readings on a thermometer will vary from one day to the next; therefore, the thermometer should be tested on the day the candy will be made. Overcooking the candy will result in candy that is harder than intended. Undercooking the candy will result in candy that is too soft, never sets properly, or will not hold its shape. Another key factor when using a candy thermometer is to ensure the bulb of the probe does not touch the bottom of the pan. The reading should come from the center of the water or candy mixture..

To test the thermometer: Fill a 2-quart saucepan half full with water. Place a lid on the pan. Heat on high until the water boils. Remove the lid. Insert the thermometer. Leave the thermometer in the pan for several minutes. .

Water boils at 212 degrees F. If the thermometer reads 212 degrees, cook the candy recipe as instructed by the recipe. If the thermometer is reading 214 degrees F, add 2 degrees to the recipes instructions. Therefore, if a recipe states to cook to 238 degrees F, cook to 240 degrees F instead. If the thermometer reading is 209 degrees F, subtract 3 degrees from the recipe instructions. Therefore, if the recipes says to cook to 238 degrees F, cook to 235 degrees F instead.