It's happened to all of us—you're making a beautiful batch of caramel or toffee and all of a sudden you notice a thin, oily layer on top of your candy. Toffees and caramels both contain butter and sugar in high quantities. If the toffee or caramel is not handled properly during the cooking process, the butter sometimes separates from the sugar and forms an oily layer on top of the candy. This often happens during the cooking stage, but sometimes it separates as it is being poured out onto a baking sheet to cool.
One of the most common triggers is when the candy has undergone an abrupt temperature shift, either becoming too cold or too hot in a very short period of time. Monitor the temperature with a candy thermometer, and try not to "shock" your candy by drastically turning the heat up or down during cooking or even moving it around on the burner too much.
It is especially important to watch the candy at the beginning of the cooking process while the butter and sugar are melting together. If the two elements melt unevenly it can result in separation. If you have good stovetop burners, we recommend turning them to medium-low to allow the butter and sugar to melt gently in the beginning stages. If the heat is too high, but butter might melt too quickly and can separate from the sugar.
Toffee and caramel can also separate if the recipe calls for constant stirring and the candy isn’t stirred often enough. Take a recipe seriously when it tells you to stir constantly—give your arm a workout and never stop stirring until the specified moment.
Additionally, separation is more likely to occur when using thinner (cheaper) saucepans, as they don’t conduct heat efficiently and lead to “hot spots” that can cause uneven heat and allowing the butter to separate. Finally, humidity can cause the butter to separate, so if your kitchen is very warm and humid, it’s not a good time to be making candy.
How to Fix It
If your candy separates during the cooking process there is a chance you can save it. Sometimes separated toffee or caramel can be saved by removing the saucepan from the heat and stirring constantly until it comes back together into a smooth mixture. Gradually return it to the heat, stirring constantly. You can also try adding a spoonful or two of very hot water to the toffee to help it come together. Start with one tablespoon and stir the candy to help it come together. Add additional spoonfuls if necessary, but do not add more than 1/4 cup of hot water total.
If you have already poured your candy out to cool by the time it separates, the candy is unfortunately too far gone to save. However, once it solidifies, you can try wiping off the excess oil and crush the toffee to use to top baked goods or ice cream.