Which ingredient is added to create a variation known as a White Russian?

The White Russian is a classic cocktail that combines vodka, coffee liqueur, and cream. The inclusion of cream is essential as it not only contributes to the drink's distinctive creamy texture but also balances the flavor of the vodka and coffee liqueur. When cream is added, it gives the cocktail a rich and smooth quality, making it different from its counterpart, the Black Russian, which only includes vodka and coffee liqueur.

In contrast, lime juice, grenadine, and mint do not fit into the flavor profile of a White Russian. Lime juice would introduce acidity and tartness, grenadine would add sweetness and a fruity flavor, and mint would introduce an herbal note, none of which would create the desired creamy and coffee-forward effect that characterizes a White Russian. Therefore, cream is the defining ingredient that transforms the cocktail into this specific variation.