From the ArcaMax Publishing, Gardening Newsletter:
http://www.arcamax.com/news/gardening/s-1909-465280
Question: I have a peppermint plant and would like to know what I need
to do to it to create the flavoring. Do I use the leaves or flowers?
Answer: Peppermint is a type of mint. Normally one simply uses the
leaves, either fresh or dried. The leaves have the best flavor if
harvested just before the plant blooms. Fresh leaves are good in iced
tes, lemonade, fruit salad, cucumber salad and so on. Dried leaves can
be used in Middle Eastern recipes and tea as well as in baking.
To dry, cut the mint near the base of each stem, tie the stems into
bundles using rubber bands at the cut ends. Then hook the rubber bands
on bent paper clips and use those as hooks to hang the bundles--hook
them onto an ordinary coat hanger, for instance. Hang them in a cool,
dark, dry, well ventilated spot until crispy. Then remove the leaves
from the stems and store in airtight packages such as jars or zipper
bags, again in a cool, dark, dry location. Make sure there is no
condensation in the container--that means it is not dry enough yet.