
Orange peel is the outer rind of the orange, used in drinks for the oil in its outer layer rather than for any liquid it holds.
Cut a wide strip with as little white as possible. Hold it skin down over the glass and squeeze once. The oil sprays across the surface, and the drink smells of orange before it is tasted. Wiping the rim afterward puts the same oil where the lip lands. Flaming it, with a match held between the peel and the glass, caramelizes the oil and tastes toasted. That suits an Old Fashioned and overpowers anything delicate.
Mandarin or tangerine peel
The closest substitute, offering a softer and sweeter aroma.
Lemon or grapefruit peel
Either works perfectly. The aroma simply shifts toward that specific citrus.
Grated zest
Grate it directly over the glass for aroma. If you stir the fine shreds in, you will have to fine-strain the liquid.
Without fresh fruit, a single dash does the trick. It provides an orange note along with a little spice.
A strip with white pith
The white pith underneath adds a slight bitterness. Trim it away with a knife or try to peel much more thinly.
Cut to order, since the oils are gone within the hour and a limp strip is a poor garnish besides. A whole orange keeps two or three weeks refrigerated. Thick-skinned fruit peels more cleanly than thin, so a navel is easier than a juicing orange.