Generally, when this happens, the mixture has warmed up or cooled off too quickly. If you notice your caramel is taking a while to come together, we recommend slowly increasing the temperature of the flame, rather than turning it up high quickly. If the mixture becomes too hot, remove it from the heat momentarily and whisk constantly until the sauce begins to form again. Add the pan back to the stove over low heat, and gradually increase it to medium heat, whisking constantly to help it come together.