Time effective technique for separating mint leaves from stems
Separating the leaves of mint from the stem is only necessary if the stem is woody, which partly depends on the variety and age of the mint. The stems of young mint shoots on most varieties of plant are tender and full of mint flavor, so can be used in dishes. Once they get older the shoots become stiff and woody, and can't be left in dishes or pureed. You can still use them to flavor dishes if you remove them before serving, but if you want the leaves to stay in you must remove the leaves. 

The best way to remove leaves is to hold the tip of the branch with one hand and loosely grip the branch with your other, then slide your hand down the branch. This pulls the leaves off without you having to pick them off.