Which whiskey production method utilizes the residue from the first distillation in subsequent fermentation?

Sour mashing is the correct answer because it involves using the leftover mash from a previous distillation process to start the yeast fermentation for the next batch. This method is particularly beneficial as it helps to maintain consistency in flavor and acidity levels throughout the production process. By incorporating the residual mash, distillers can introduce natural enzymes and lactic acids that enhance the fermentation environment, thereby improving the overall quality of the whiskey.

In context, continuous distillation typically refers to a method where the distillation occurs in a continuous flow rather than in batches and does not focus on the use of residual mash. Double distillation involves distilling the wash twice to increase the alcohol content and refine flavors, but it does not utilize mash residues in its initial fermentation process. Single pot still whiskey is primarily produced from a mix of malted and unmalted barley in a pot still but also does not involve sour mashing techniques.