Using a Candy Thermometer
Always use a thermometer designed for candy making. It must have a movable clip that’s used to secure it to the side of the pan and to keep the end of the thermometer off the bottom of the pan. Be sure to read the thermometer at eye level.
Check your candy thermometer for accuracy each time you make candy. Place the thermometer in a saucepan of boiling water for several minutes before reading. If the thermometer reads 212° in boiling water, it is accurate. If it rises above or does not reach 212°, add or subtract the difference to the temperature called for in the recipe.
A candy mixture will cook very slowly when boiling until it reaches 220°, then it will cook quickly. It’s important to closely watch the thermometer at this point.
To avoid breakage, allow the thermometer to cool before washing it.