By Harold McGee
Terpene compounds are constructed from a zigzag building block of five carbon atoms, which turns out to be amazingly versatile and can be combined, twisted, and decorated into tens of thousands of different molecules. Plants usually produce a mixture of defensive terpenes. They are characteristic of the needles and bark of coniferous trees, of citrus fruits, and of flowers, and provide pine-like, citrusy, floral, leaf-like, and “fresh” notes to the overall flavor of many herbs and spices. As a family, terpenes tend to be especially volatile and reactive. This means that they’re often the first molecules to reach the nose, and provide the initial impression of these lighter, more ethereal notes. It also means that they’re readily boiled off or modified by even brief cooking, which is why these fresh, light notes disappear. If desired, they can be restored to a cooked dish by adding a new dose of the herb or spice just before serving.