Pick out the mint you will use. Oil is extracted from both leaves and stems. If you are using mint from your garden, water plants thoroughly for several weeks before harvesting.
Wash the mint with water. Remove any brown wilted areas.
Pack the mint into a plastic container. Fill the container completely, then saturate the mint with premium vodka. Cover the mint, and let soak for five weeks.
Remove the plant pieces from the container and save the liquid portion. Freeze it for two days. Alcohol does not freeze well, so when you remove the container from the freezer, the mint oil will be the frozen portion. Drain off the liquid alcohol. Rinse the ice with water to remove the residue from the vodka. Put the ice in a container and let it thaw on a shelf or in a pantry. This is mint oil.
Store the oil in a capped bottle. Keep the bottle on a cabinet shelf, out of the sun.