Generally, cilantro oil refers to one of two things: vegetable oil that has been flavored with cilantro for cooking, or distilled essential oil from the cilantro plant. The cooking form of cilantro oil is made by soaking cilantro in oil to give the oil some of the cilantro plant's flavor. This oil is a common ingredient in many types of cuisine, and is used as a condiment on many Chinese-American dinner tables. A different type of oil that is extracted straight from the plant, essential cilantro oil is not edible in a cooking sense, and is made for herbal medicine purposes.
A few techniques may be used to make cilantro oil, so it often comes out looking different depending on how it is made. A common method for making homemade cilantro oil is to blend fresh cilantro into oil. Since these are mild-flavored oils that allow the cilantro flavor to stand out, most of the time, cooking oils flavored with cilantro are made with corn oil or canola oil. Homemade blended cilantro-flavored oil can be used immediately for cooking as it is, or it might be strained into a preparation that looks more like everyday vegetable oil. Another less common method of making this oil is to soak dried cilantro in a sealed container of oil for a long period of time.
When cilantro oil is strained, it is pressed through a sieve or cheesecloth to remove the particulate matter, yielding transparent, cilantro-flavored oil. Most people making this oil at home leave the cilantro in the preparation. Cilantro oil with the cilantro left in the mixture looks like a green herbal paste similar to pesto, but it is usually blended into a finer paste than the paste generally used for pesto.
Cilantro, also called Chinese parsley, is the leafy green part of the coriander plant. In general, people refer to the leaves as cilantro and the seeds and roots as coriander. Coriander seeds are commonly used as a spice, which is ground into a powder and used as seasoning in many food items and beverages, including curried stews, pickles, and beer. Ground coriander seeds have a lemony, citrus flavor, while cilantro leaves have a sharp green flavor and strongly herbal aroma.
When it comes in the form of essential oil, cilantro oil is not for cooking. Many essential oils are flammable after they are distilled using steam. Cilantro essential oil is made for use in cosmetics, soaps, and lotions. It is generally not consumed, although small amounts may be ingested or inhaled medicinally as directed by a qualified herbal medicine practitioner.