
A sugar cube is a pressed block of white sugar for single-portion sweetening, roughly a teaspoon.
A cube is a ready-made measure of sugar. In an Old Fashioned it is muddled with bitters; in a Champagne Cocktail it goes in whole, soaked with bitters.
A barspoon of 2:1 syrup replaces one cube, or about 7 ml of 1:1, with no muddling needed. It mixes into a cold drink at once, but will not send up bubbles in sparkling wine.
Granulated sugar
A level teaspoon replaces an average cube. Cubes weigh from 2.5 to 8 g, so taste and adjust.
Demerara cubes
One replaces one white cube. It adds a faint toffee note that pairs well with whiskey or aged rum.
Kept dry, a box of cubes outlasts most of the bar. Damp is the only thing that ruins them: they swell, fuse to each other and stop being a measure.
Brut Champagne