Before modern refrigeration, how were casks traditionally cooled?

Using external evaporative cooling was a common method employed before modern refrigeration to cool casks. This process utilizes the natural phenomenon of evaporation, where water on the surface of the cask can evaporate, absorbing heat in the process and thereby cooling the contents of the cask. This method is effective due to the heat transfer properties of water as it changes from liquid to vapor.

In essence, casks could be wrapped in wet materials or placed in humid environments, allowing evaporation to take place and lower temperatures inside the cask. This method was not only practical but also relied on principles that have been used in various traditional cooling systems, similar to how evaporative coolers operate today.

Other methods, such as adding ice directly to the cask, while possible, were not as commonly used on a large scale due to the challenges associated with obtaining and using ice, especially in warmer climates. Placing casks in cold water could offer temperature regulation to a degree, but the effectiveness would depend highly on the water temperature and surrounding conditions. Lastly, while underground cellars were utilized for storage and some degree of temperature control, they were not universally applied for cooling casks in all brewing traditions, hence limiting their application as a primary cooling method.