
Orange zest is the coloured outer layer of an orange's peel, prized for the aromatic essential oils it carries.
Aromatic orange oil dominates, bright and fragrant, carrying only a faint bitterness and no sweetness or acidity.
Used as an expressed twist or a pared garnish, it is twisted or squeezed skin-side down over the surface to release its oils, then often dropped in; pare it thinly to keep the bitter pith out. It contributes aroma rather than any measured flavour.
Another citrus zest such as lemon or grapefruit can stand in for the visual and aromatic accent, though it shifts the aromatic character rather than reproducing the specific orange-oil scent.
Zest is specifically the coloured outer layer (flavedo) carrying the aromatic oils, while 'peel' can mean the whole skin including the bitter white pith; zest deliberately excludes that pith.
The flavedo — the coloured outer skin of the fruit — holds the orange's essential oils, and it is pared, scraped or grated away from the bitter white pith (the albedo) beneath. A twist is a strip of this peel taken for expression over a drink.
The volatile oils dissipate quickly once the zest is cut or expressed, so it is best prepared fresh at the point of use.