Flavored extra virgin olive oils are manufactured by adding ingredients to the olives as they are being pressed. Lower quality grades of olive oil are enhanced only after the oil has been produced. A heat treating process is used to infuse the oil with flavoring agents. Citrus extracts and citrus zest, such as the lemon zest pictured at the left, are popular additions to olive oil. Various herbs and spices such as garlic, basil, rosemary, and pepper are also used.
It is not safe to prepare homemade flavored olive oils unless they will be used immediately. Special processes are used in commercially prepared flavored oils to make them safe for the consumer. Homemade flavored oils may promote bacterial growth that can cause illness.