Final answer:
Coffee urns can be cleaned by using vinegar to dissolve and remove lime deposits that can build up and slow down the brewing process.
Step-by-step explanation:
Coffee urns can be cleaned by using vinegar, which contains dilute acetic acid. Lime deposits can build up over time in the coffee maker, causing the brewing process to slow down. By putting vinegar in the urn and running it through the brewing cycle, the vinegar dissolves the deposits and cleans the maker, restoring the brewing process back to its original rate. It is important to run water through the brewing process after using vinegar to avoid getting unpleasant-tasting coffee.