
Grapefruit juice is the tart, faintly bitter juice pressed from grapefruit.
Its bitterness gives a drink a structure that lemon or lime cannot. It carries rum in the Hemingway Special Daiquiri and vodka in the Sea Breeze. White grapefruit is the more bitter choice, pink the softer one.
Fresh pink grapefruit juice
Close to white in sugar and acid, so use the same amount. It has fewer bitter compounds, so the taste is softer.
Bottled grapefruit juice
Works one for one. Choose 100% juice, pink or white, and expect a flatter taste than fresh.
Orange and lemon juice
Mix three parts orange juice with one part lemon juice. It comes fairly close in sweetness and acid but has no bitterness. A dash of grapefruit bitters brings some of it back.
Do not use. It is sweet and has little juice, so it will not give the acid you need.
Fresh juice keeps a day refrigerated and turns more bitter as it stands rather than losing flavor. Whole fruit keeps two or three weeks chilled, and a heavy fruit for its size has more juice in it.