Why did old time bottle caps have cork inserts?

Old-time bottle caps often had cork inserts to create a better seal for preserving beverages, particularly carbonated drinks. The cork provided a tight fit that helped prevent gas from escaping and minimized the risk of contamination. Additionally, cork was more pliable and could accommodate slight variations in bottle openings, enhancing the sealing effectiveness. This practice was eventually phased out in favor of metal caps with plastic liners that offered improved durability and sealing properties.