Adjusting Your Thermometer for High Altitude Candy Making

You Will Need to Adjust Your Thermometer

Sugar boiling

The Spruce

If you live at a high altitude, chances are you're familiar with some changes you need to make when baking bread and cake. The difference in air pressure at higher altitudes means that baking times, temperatures, and sometimes even ingredient ratios need to be tweaked to get the best outcome. But did you know you might also need to make adjustments in your candy making to compensate for high altitudes?
If you are at a high altitude and do not make any changes to your candy recipes or procedures, you will most likely end up with overcooked candy. This is because water boils at lower temperatures at higher altitudes, so you do not need to cook your candy as long, or to as high a temperature, as you would at sea level. So what adjustments are necessary for high altitude candy making? Good news! There are two ways of doing this, and it is actually a really easy fix involving only the candy thermometer.

how to perform boiling water test with candy thermometer
Illustration: Chloe Giroux. © The Spruce, 2019 

The Boiling Water Test

Depending on your actual altitude, the adjustments you need to make will be different, so the easiest and most reliable way to figure out what temperature conversions you need to make is to perform the boiling water test with your candy thermometer. You simply submerge the thermometer in boiling water and note what the temperature is five minutes after the water comes to a boil (which is 212 F/100 C at sea level). This is the best way since not only will it account for your altitude, but it will also take into account any irregularities or inaccuracies with your specific candy thermometer.

Make Some Calculations

However, if you do not have time to test your thermometer in boiling water, or if you just want a general idea of how to adjust candy temperature recipes, here is a handy rule of thumb: Subtract two degrees Fahrenheit from a stated temperature for every 1,000 feet you are above sea level.​

For instance, if you live at 2,000 feet above sea level, your approximate conversion would be four degrees less than the stated candy temperature. So if you were making a recipe that called for the candy to be brought to 240 F, you would only boil it to 236 F.

Another example: if you live at 6,500 feet above sea level, your conversion factor would be 13 degrees less (2 x 6 [thousand feet] + 1 degree for that extra 500 feet). If your recipe called for 280 F, you would only cook your candy to 267 F. As you can see, the higher the altitude, the more important it is to do this conversion. Even a few degrees can make a huge difference in the successful outcome of the candy.

Remember, this is just an approximation, and for a more accurate conversion formula, you should do the boiling water test on a regular basis.