What is the main purpose of using a mug to serve Spanish Coffee?

Using a mug to serve Spanish Coffee primarily serves to insulate the heat of the drink. Spanish Coffee is typically made with hot coffee, and serving it in a mug helps maintain the temperature, allowing the drinker to savor the warmth of the beverage longer. Mugs are designed to retain heat effectively, ensuring that the coffee remains enjoyable without cooling down quickly.

The other options, while they may have their merits in different contexts, do not accurately reflect the primary function of a mug in this scenario. For example, while presentation is important in serving any drink, the main purpose of a mug goes beyond aesthetics to provide functional heat insulation. Similarly, though stirring is part of the process of preparing this coffee, the design of a mug isn't inherently aimed at facilitating stirring, as traditional utensils would serve this purpose better. Overall, the insulating properties of the mug make it the ideal choice for serving hot beverages like Spanish Coffee.