BARCELONA—Catalan nationalist and beverage entrepreneur Ramon Carner is trying to promote his region’s separation from Spain one sip at a time.

For young people, he sells an energy drink called Desperta Ferro!—or Awake Iron!, a Catalan battle cry from the Middle Ages. For rum drinkers, he markets a brand named for Christopher Columbus, who some nationalists insist was really a Catalan rather than Genovese. For others, there is Catalan Cola.

Mr....