Why do bartenders insist on fresh citrus juice?

The answer

Bartenders insist on fresh citrus juice because it tastes bright and lively, while juice that has sat for hours or been bottled often tastes flat or slightly bitter. Many classic cocktails depend on a balance between sweet and sour, so the quality of the citrus has a large effect on the result. Squeeze juice on the day you plan to use it and keep it cold. If a recipe tastes too sharp or too sweet, adjust the syrup a little.