12. Leather

Leather-aged cocktails are a recent trend in the bar industry. Depth of flavour is added by placing spirits inside wineskins or goat-leather bota bags. When it comes to this method, the most important safety aspect is ensuring that the leather of such vessels has been certified for food use.

That would mean using a special tanning process, as the most common one uses many chemicals among which is chromium, a compound potentially harmful to human health.