Although not the most prevalent garnish, orange slices, wedges, twists and spirals can lend a zip of citrus flavor to a cocktail in the form of orange juice from the flesh, or orange oil from the peel. Try an orange garnish in any cocktail made with orange juice, orange-flavored alcohol, Collins mix and sour mix.
A plus in many cocktails, orange slices are a must in an old-fashioned. Muddle an orange slice with sugar and bitters; fill the glass with whiskey or brandy. Crosswise slices between 1/8 and 1/4 inch thick are ideal, but cut larger slices in half to make half-moon shapes. Try putting a literal twist on the basic orange slice. Make one 1/8-inch-thick slice halfway through the orange followed by another 1/8-inch-thick slice all the way through the orange. Cut a slit at the center of the 1/4-inch half. Twist the 1/8-inch flaps around and tuck them into the slit.
Juice and oil drips from orange wedges served on the rims of glasses, leaving it up to the consumer to squeeze in more juice to taste. Cut the orange in half lengthwise from stem end to blossom end. Cut each half lengthwise into four equal pieces to make one-eighth wedges, or into one-sixteenth wedges for large oranges. For wedges that rest perpendicular to the glass, cut the center of the wedge through the flesh, stopping short of the white pith layer. Cut a slit between the flesh and pith layers at one end to stand the wedge upright on the rim.
Small orange twist garnishes float on the drink surface so you can pick them up and twist to release the citrus oils into the cocktail. The orange-colored rind is also rubbed along the glass rim to enhance each sip with a note of citrus. Hold the orange in your non-dominant hand and position the knife near the stem end. The blade should run perpendicular to the imaginary line running between the stem and blossom ends. Dig the knife through the rind, slipping the blade between the rind and pith layer. Cut down toward the blossom end to remove an oval piece of orange rind roughly the width and length of your thumb.
Orange spiral garnishes hanging from a cocktail glass rim make a drink appear fun and fancy, and also add citrus oil and citrus notes. Create even-width strips of peel without digging into the pith using a channel knife, which is similar to a vegetable peeler except the blade is narrower. Hold the knife perpendicular to the way you would work a vegetable peeler. Dig the blade into the orange at a point near the stem end. Drag the knife around the orange to cut the strips as long as possible without breaking. Wrap the strand around a chopstick or toothpick and pull tight to form a spiral shape.
References and ResourcesSerious Eats: Cocktail 101: A Guide to Garnishes
Serious Eats: Cocktail 101: More Fun with Citrus Garnishes
The Kitchn: Cocktail Basics: Citrus Garnishes 6 Ways
Bartending School: Garnishes
Canadian Living: How to Make a Fancy Double Orange Twist Garnish
Serious Eats: Cocktail 101: How to Garnish With a Citrus Twist
Serious Eats: Cocktail 101: How to Cut Citrus Wedges
Food & Wine: Cocktail Basics: Techniques