Even when I calibrated a really nice digital kitchen thermometer to account for the temperature difference at which which water boils at altitude, the temperature did not rise uniformly. As I stirred the boiling water with the probe to get a uniform temperature the reading would rise and fall. I have a couple of batches of rather tough jam because the reading needed to be 228° (all temperatures are just examples). I could not leave the probe in the syrup because of a poorly designed support mechanism to hold it on the pan. I would put the probe in and it might read 223°, so I would let it cook a bit longer. Then it might read 220°, the next reading might be 226°, ,and a few minutes later 224°. Because I did not grow up at altitude, I rely on a thermometer in addition to testing the old fashion drip from a spoon method. Can you recommend an accurate candy thermometer?
Fremont County Colorado
You want to get a thermometer that can be attached to the edge of the vessel in which you are making the candy. A really good one is this one:
An article reviewing various candy thermometers is here:
Adjust cooking temperature for altitude. Just as water boils at a temperature below 212° F at higher altitudes, all other liquids boil at lower temperatures. When sugar mixtures are cooked at sea level recipe temperatures, faster loss of water causes the mixture to become too concentrated. To adjust candy recipes for high altitude, reduce the cooking temperature. The chart below lists cooking temperatures for various types of candy.
STAGE CANDY TYPE DEGREES FAHRENHEIT
Sea Level 2,000 ft 5,000 ft 7500 ft
Soft Ball Fudge, fondant 234-240 230-236 224-230 219-225
Firm Ball Chewy caramel 242-248 238-244 232-238 227-233
Hard Ball Nougat, marshmallow 250-268 246-264 240-248 235-253
Soft Crack Taffy, butterscotch 270-290 266-286 260-280 255-275
Hard Crack Toffee, brittle, lollipops 300-310 296-306 290-300 285-295
A helpful hint for adjusting your candy cooking temperature is to lower it by 2 degrees Fahrenheit for every 1,000 feet you are above sea level. So, if you live 5,000 feet above sea level, you would lower your cooking temperature by 10 degrees.
Hope this has been helpful.