"I live at 5400 feet altitude; what adjustments do I need to make when making toffee?"
I asked Institute of Culinary Education baking and pastry arts chef-instructor Jeff Yoskowitz, who told me he ran into the problem himself when visiting his wife's family in Quito, Ecuador, which is 9200 feet above sea level. He follows the guidelines below as a general rule, but finds he often has to tweak the amount of fat and liquid in the recipes by trial and error.
At sea level:
244-248° firm ball
250-266° hard ball
270-290° soft crack
295-310° hard crack
For every 500 feet over sea level, drop the temperature by 1 degree. At 5000 feet, for example:
234-238° firm ball
240-256° hard ball
260-280° soft crack
285-300° hard crack
For more tips on making candy, see The 7 Deadly Sins of Candy Making.
Recipe: Salted Chocolate-Pecan Toffee