The butterscotch flavor develops naturally when you boil sugar syrup and butter together to a high enough temperature to make hard candy. It’s a combination of two flavors: browned sugar, otherwise known as caramel, and browned butter. The browning results from what chemists call the Maillard reaction, in which sugars and proteins react under heat to create roasted and browned flavors. This is why butterscotch has so often been combined with other roasted ingredients. Nuts, such as pecans, are typically roasted; rum and Bourbon contain caramel; maple syrup has undergone the Maillard reaction. [Perry]
Perry, Charles. “Boss sauce.” The Chicago Tribune. 21 April 2004. <www.chicagotribune.com/features/food/chi-0404210083apr21,1,183784.story> (23 April 2004).