How long can melted salted caramel last

I make orange caramel at work for one of our desserts.

You will need:

• zest of one orange. big chunks is fine
• 2 cups sugar
• 1 cup water
• 2oz grand marnier/cointreau/triple sec (optional)
• approx 1/2c butter, unsalted
• approx 1/2c 35% cream
• generous pinch kosher salt
• 1-2tbsp pulp-free lemon juice

Combine the first three ingredients in a saucepan. Brush the exposed sides of the pan with lemon juice--this prevents crystallization. Dissolve the sugar in the water over medium heat, turn down to low simmer for 20 minutes. Strain out the zest, return sauce to heat, bring to boil. Cook until the sauce has taken a light amber colour, pour into stainless steel bowl. Whisk in butter, then cream, then grand marnier if using, then salt.

I would say there are 2 problems here: the lack of water, and the constant stirring. Try adding 1/4 cup of water to the sugar - this should stop it catching and burning.

You should avoid stirring caramelising sugar because you run the risk of flicking bits of it onto the side of the pan. These isolated bits cook faster and thus burn, then drop into the rest of the sugar. Result: bitter caramel. Stirring also promotes crystallisation, which is not what you want for a smooth sauce.

If you have to stir it, do it slowly, carefully, and infrequently - only as much as necessary to distribute the water evenly through the sugar.

I would also use a sugar or probe thermometer to ensure you're not over-cooking the sugar - get it to 350ºF, then take it off heat. This will take 6-8 minutes, and it will be a dark amber colour. Let it stand for 1 minute before whisking in your cream (I normally gently heat the cream beforehand by the way, and add a teaspoon of sea salt to it, because salted caramel is effing gorgeous).