This is a well-known hydrodynamic instability known as the [Plateau-Rayleigh instability][1]. 

In short, liquids, because of surface tension at the liquid-gas interphase, tend to minimize their surface area. A liquid column of volume $V$ always has a larger surface area than $n$ droplets of volume $V/n$. 

As it turns out the length at which point the liquid column will start to break up is found by the heuristic:
$$\kappa R_0 \approx 0.697$$
where $\kappa$ is the wave number and $R_0$ is the initial radius of the column.

  [1]: https://en.wikipedia.org/wiki/Plateau%E2%80%93Rayleigh_instability