Do candy making temperatures change at high altitude?

Question

Do temperatures, when making candy (soft ball, soft crack, hard crack, for example) need to be adjusted for high altitude? If so, is there a rule or chart that applies?

Answer 1

According to Colorado State University Extension, you should subtract 2°F for every 1000ft above sea level from the target temperature, when making candy.

From their foodsmartcolorado.colostate.edu

This adjustment allows the candy maker to control the degree of evaporation necessary to achieve the proper sugar concentration for the desired end product.

At sea level, the boiling point of liquids is 212°F, but for every 500 feet above sea level, the boiling point decreases by 1°F due to less resistance on surface molecules. For example, at 5,000 feet water boils at 202°F, which is 10 degrees less than at sea level. The lower the boiling point, the quicker evaporation occurs, so at higher elevations, this faster loss of water can result in a sugar mixture either becoming too hard or grainy if the recipe is not adjusted for the elevation.

Answer 2

Long story short - yes. However, it will be only to an extent and it is dependent on the exact point at which you are making the candy. As far as I know there isn't any sort of chart, though it should be fairly easy to make one with some experimentation if you have a sugar thermometer.

The boiling of liquids at lower temperatures at lower air pressures (as you get at altitude) are related to the pressure of the gasses against the liquid surface (This is a simplistic view, but it works), basically this means that the gas above holds the water in so that it can less easily evaporate. At boiling point, the energy in the liquid allows the water molecules to have high enough energy to push back and freely escape the system. There's a more complex explanation over at the Physics SE

When you make candy you initially boil a sugar solution to drive off the water and get the sugars to fragment, react with each-other, and drive off natural water contained in the sugar molecule itself in the process called caramelization. You don't evaporate the sugar itself much at all, so that bit is independent of pressure (I think).

To quote the linked Bakerpedia:

First stage – thermal decomposition and fragmentation to yield glucose and fructose. These sugars can individually lose water and react with each other.

Second stage – isomerization of fragmented sugars (aldoses to ketoses) and further elimination of water to form the sugars’ anhydro forms.

Third stage – additional fragmentation, polymerization and subsequent formation of volatile flavor compounds such as furan, maltol, ethyl acetate, diacetyl, etc. as well as brown colored compounds such as caramelan, caramelen and caramelin.

The water content and temperatures below for each of the physical stages (i.e. soft ball, hard crack etc.) at normal cooking conditions are taken from this page from The Flavour Blender:

Stage	Temp range (C/F)	Sugar content (%)
Thread	106-112 / 223-235	80
Soft ball	112-115 / 235-240	85
Firm ball	115-121 / 240-250	87
Hard ball	121-130 / 250-267	92
Soft crack	132-143 / 270-290	95
Hard crack	146-154 / 295-310	99

As you can see, there is still quite a lot of water in the last two stages. Because the temperature at which water boils off will be constrained by the altitude, it will be harder to reach the first stage and then progress to the next stages as the physical temperature of the mix will be lower.

However, I suspect (without actually trying it) that once you reach the desired water concentration, the temperature of the mix should rise to meet the suitable point. This will take longer than it would at sea-level. The last 2-3 stages might well be independent of the water content and take the same sort of time as you would expect, as these stages are more about reactions of the sugar molecules than driving off water.