Post-fermentation by aging breaks down the caffeine levels in pu-erh, meaning that the caffeine content naturally diminishes the older it gets. This means that a very old pu-erh might have trace amounts of caffeine by the time it is consumed in comparison to a younger pu-erh. That being said, the actual caffeine content present in a cup of pu-erh tea varies upon how long the tea is steeped. The longer the steep time, the more caffeine the tea will contain. Caffeine content will lessen each time tea is re-steeped.