What are the two unique features of a pot still used in Cognac production?

In Cognac production, the pot still is notable for its traditional and distinctive characteristics, which are captured in the chosen correct answer. Firstly, pot stills used in Cognac must be heated directly with flames. This direct heating is essential in order to facilitate the appropriate distillation process for the rich and complex flavors characteristic of Cognac. The traditional method relies on direct flame, allowing for careful control over the heat during distillation.

Secondly, the use of a 'worm tub' condenser is another unique feature of these pot stills. The worm tub is a coiled tube that is submerged in cool water, where the vapor condenses back into liquid. This method is significant in Cognac production, as it allows the distillate to cool gradually, resulting in a smoother spirit that retains the desired aromatic characteristics.

These features reflect the historical practices in producing Cognac and contribute to the overall quality and profile of the spirit. The other options listed do not align with the traditional practices associated with Cognac production.