Like many other herbs, peppermint plants have essential oils that are often used for aromatherapy. Most store-bought peppermint oils go through a distillation process where the leaves are held over steam, which in turn releases extremely concentrated oil. Peppermint can also be made at home without the need for a still. Although not as concentrated as the store-bought products, the homemade oil can be used in the same ways.
Wash a 12-oz. glass jar, along with the lid, and a knife in hot water and dish soap. If you have a dishwasher with a sterilization setting, you can use the dishwasher instead. Let the objects air dry.
Inspect the peppermint plants and discard any brown or wilted leaves. Put the healthy leaves into a single pile on a cutting board.
Chop the peppermint leaves with the knife to encourage them to release their essential oil. A coarse chop is all that is necessary. Fill the jar with the chopped leaves.
Add vegetable oil to a skillet and put it on the stove at medium heat. Use just enough oil to cover the peppermint leaves. If the jar is filled to the top with leaves, you'll need 1 1/2 cups of oil.
Check the temperature of the oil with a cooking thermometer every couple minutes. Remove the oil from the heat when it reaches 160 degrees Fahrenheit.
Pour the oil into the jar. Seal the jar and store it in a dark place for a month.