Wash and dry any fresh herbs you use. This includes fresh herbs, peels, or other ingredients that aren’t dried. You don’t want water in your oil. For fresh herbs, I recommend hanging them upside down in the air for 24-48 hours to remove any moisture.
Add the olive oil and choice of flavor infusions such as fresh herbs, dried chilis, or lemon peel, to a small saucepan. Heat the oil slowly over medium low heat to about 150 degrees for 20 minutes. It should not bubble, boil, or spatter.
Remove from heat and let the oil cool. If desired, strain the herbs or peels out of the oil.
With a funnel, pour the oil into a bottle with enough oil to cover the herbs by at least one inch. Seal the bottle and store in refrigerator, particularly if you have garlic, fresh herbs or fruit peels in the oil.
How long the oil will last depends on what you put in it. Most dried herbs will last around 2 months, but fresh herbs and peels will last at least 2 weeks, perhaps a month when stored in the refrigerator.