Distillation, as a process, has been known since at least the first century AD. Yet a readily reproducible process of distillation did not really take off until the 13th century or so. Why the gap of 1000 years?
The answer is almost banal. Yes, a handful of people knew how to distill. The problem was with the technology. Glass broke easily, and ceramic implements were little better, as they transferred heat ineffectively, and inconsistently, depending upon the mineral content of the ceramics. In short, no one knew how to make good distilling vessels.
It was the Venetians, who combined different glass-making techniques (Roman and Syrian), that were able to consistently produce high-quality glassware. However, this didn’t occur until the mid 1200′s in history’s timeline. Once this glass took off, distilling on a regular basis took off soon afterwards.
Here’s an interesting side-note: You can still see remnants of Venice’s glass industry in work if you visit the city. Murano island has all sorts of places that both sell and pay homage to the industry that helped solidified Venice’s empire.