Precautions – Make sure your candy thermometer is calibrated!
One foolproof method is using boiling water. First, leave the thermometer in the pot without the tip touching the bottom (it should be raised by a centimeter or so). Then bring the water to a rolling boil. The thermometer should read about 212°F (100°C).
If the thermometer is off by a few degrees, make sure to add/subtract the same number when cooking candy. For example, if the thermometer reads 215°F after boiling water, remember to add 3°F each time.
Cheap thermometers can be off by as much as ~20 degrees. Also, having the tip of the thermometer making direct contact with the pot’s bottom can make the temperature readings fluctuate greatly.
How to handle high humidity for candy-making
Increase cooking temperature by a few degrees or increase time under heat.
For example, when making hard candy, the hard crack stage is around 300°F (149°C). Depending on how high the humidity is, you’ll have to increase cooking temperatures to compensate.
A general rule of thumb (not perfect but a good place to start) is to increase by 2°F for each 10 RH above 35. A humidity of 55% RH will need a cooking temperature of 304°F.
If you are worried about burning the sugar, you could also cook longer than usual or reduce the amount of water used.
Use a dehumidifier in the cooking area beforehand.
This temporary solution is not perfect, but it definitely helps. Make sure any doors or windows open to the outside environment are closed.
Running a range hood while cooking candy can slightly help as well.
Also turning on the AC to make the room cooler will help the candy set sooner.
What’s the ideal humidity for making candy?
Relative Humidity (RH) of below 35% is ideal for making candy without negatively impacting the texture of the final product. That is why dry winters are the ideal season for making candy!
Higher humidity might force you to use a higher temperature to compensate for the extra moisture introduced to the candy. While going on the upper range of temperature can help, going too high can affect which stage of sugar cooking you’re in and can even scorch the candy.
Does rainy weather affect candy-making?
Yes, rainy weather results in higher humidity, which can cause candy to take in more moisture than desired.
The effect of humidity on fudge is even more pronounced. Excessively high humidity will cause fudge to become runny.
Store candy as soon as possible
Even if the candies turn out perfect, don’t leave them sitting out on a humid day. If the humidity is high enough, candies can start to absorb moisture from the air, resulting in an undesirable sticky coating.
Airtight containers in a cool, dry location are ideal. Another option is to wrap the candies in cellophane as soon as they set.