When making mulled wine, take care not to let the wine get to boiling or at being at temperatures above ~170°F for long periods; this is a little less than the boiling point of alcohol. If heated at higher temperatures for too long, the alcohol will start to evaporate.
According to Merriam-Webster, use of the word “mull” dates to the early 17th century, although the practice of imbibing warm spiced wine is traced to the ancient Greeks. Not to be outdone, the ancient Romans had their own version of mulled wine called Conditum Paradoxum, which was flavored with dates, peppercorns, bay leaf and saffron. Fortunately, it’s no longer necessary to make bad alcohol taste good.