Onion oil is, in most circumstances, one of two related things: either the essential oil extracted from an onion, or a base oil such as olive or vegetable, which is flavored and augmented with onions, usually during cooking. Essential oils are most common in homeopathic and alternative medicine. In cooking, onion oil is almost always aimed at providing more flavor than any health benefit.
Onion oil can refer to onion flavored oil.
Medicinal onion oil usually comes packaged in dropper bottles or capsules. The oil is highly concentrated and is usually obtained by slowly boiling the onion over time or steam drying it. Onions naturally contain a lot of moisture, which means the water must be pressed or boiled out of the vegetable before the oils can be isolated. The process is usually arduous, but not particularly complicated.
Onion oil can be made by boiling onion slices.
Homeopaths sometimes recommend natural onion oil as a treatment for upper respiratory problems, particularly colds and seasonal allergies. It is believed that the oil can help with decongestion while helping to rid the body of toxins. Oils are also sometimes used to treat ear infections. Some traditional medicine practices prescribe attaching whole onion segments to the body to achieve the oil’s healing properties, but more modern practitioners generally find the ingestion or direct application of concentrated oil to be more effective.
Several different pharmaceutical studies also look at onion oil. Most onion varieties are rich in disease-fighting vitamins and nutrients. Researchers tend to look for ways to harness these benefits and channel them into specific treatment regimens for human diseases. Some scientists believe that onion oil is capable of anything from lowering cholesterol to negating the harmful effects of nicotine and preventing the growth of some cancers. The results are largely inconclusive.
In culinary environments, onion oil is often tastier, but also less concentrated. Chefs can often extract essential oils from onions by simply heating thin slices of vegetables and then reserving the resulting liquid. Most of the time, flavor is more important than purity. Cooks often add salt and other seasonings and may or may not leave pieces of onion to fry while the oil is extracted.
Home-pressed onion oil is often used as a base for many dishes. Oil is a common facet of many recipes. Cooking with onion oil instead of commercially available versions of vegetables or corn often adds a new layer of flavor to a dish and can enhance a variety of savory and sweet flavors.
Sometimes cooks also create a kind of onion-flavored oil by boiling onion slices in other oils. Olive oil is a popular choice as its mild, nutty flavor can make a good base for spicier onions. This type of oil is popular as a seasoning and can also be used to dip breads and vegetables.