Boiling causes a loss of moisture through evaporation and concentrates the liquid; thus, the lower the boiling point, the sooner evaporation begins. Depending on the candy or sugar mixture, the results may become “sugary” or hard as the sugar re-crystallizes.
At sea level, water boils at 212°F, but at high elevations, all liquids boil at temperatures below 212°F. This requires adjustments for candy and frosting recipes, which generally use the standard 212°F boiling point for water.
Confectionary recipes should be adjusted for elevation by reducing the “finish” temperature. Using a candy thermometer, first test the temperature at which water boils. The finish temperature should be reduced by the difference between your water boiling temperature and 212°F (Table 1). While weather conditions may cause minor changes from day to day, the range is usually slight. Compare your temperature measurements and cold-water test results, and record your adjustments in your cookbook or on recipe cards to keep track of time, temperature, and the quality of the final product. The cold-water test or a candy thermometer are two ways to test for finish. When the cold-water test is used, it will be necessary to learn the feel of the mixture at different stages (soft ball, hard ball, crack, etc). Table 1 indicates adjustments for various elevations.
At 5,000 ft elevation, water boils at approximately 202°F, 10°F less than at sea level; the finish temperature for candies or frostings should therefore be reduced by 10°F. For example, if a sea-level recipe for creamy fudge gives a finish temperature of 238°F, the corrected thermometer reading would be 228°F at 5,000 ft. The cold-water test is reliable at any elevation since it depends solely upon the appearance of the candy in cold water.
You can also go to CSU Extension Farm to Table webpage and then search for high altitude and candy to find a copy of a great document that will help. When you bake, cook, or make candies at high elevation it does take a little experimenting.....that is what food science is about at high elevations. I hope this information helps you in making your fudge.
