These are so-called reducing sugars, which means they have a structure - "a funny tail," Ms. Corriher called it - known as a carbonyl group that takes part in the Maillard reaction.

In the Maillard reaction, at high temperatures, fructose and glucose in the honey reacts with amino acids in the duck, producing a variety of new molecules that add flavor and color.

The process is referred to as non-enzymatic browning or Maillard reaction, named after the discoverer.