What type of sweetener is used in a Rob Roy?

In a Rob Roy, the sweetener used is sweet vermouth. This cocktail is a variation of the classic Manhattan, traditionally made with whiskey, sweet vermouth, and bitters. The use of sweet vermouth gives the Rob Roy its distinct flavor profile, balancing the strong notes of the whiskey with its sweet, herbal characteristics. Sweet vermouth is fortified and flavored wine, making it an ideal sweetener in cocktails, as it not only adds sweetness but also complexity and depth due to its various botanicals.

The other options, while they are common sweeteners in bartending, do not apply to the Rob Roy. Simple syrup is often used in cocktails requiring a liquid sweetener for easy mixing; agave nectar is popular in tequila-based drinks; and honey, while a natural sweetener, is more commonly used in certain other cocktails. Together, they highlight the unique role of sweet vermouth in creating the classic flavor of a Rob Roy.