These days, walnut oil basks in a sort of gourmet limelight, but if you were to travel back 100 years ago in France, you'd find it disdained by most cooks. Indeed it was only the poor who at times were forced to depend upon it for culinary use. A more common practice was to use a highly refined form of it in oil burning lamps.
The unrefined version of this oil has a low smoke point indicating that it quickly breaks down and gains an unpleasant taste with heating. This makes it inappropriate for most cooking. Its current popularity stems from its use as an accent oil.
Walnut trees grow all over France, but it is Périgord (the region of Dordogne) and the area around Grenoble that are the most noted for their production. If you buy a commercial oil from France, it is most likely made in one of these two regions.
Not all oils are equal. Look at labels carefully to determine what sort of product you have in hand. There are three levels of quality:
L'huile de noix raffinée (Refined): Made from nuts that are considered ordinarily inedible, the oil is refined to eliminate any impurities. The resulting oil is flavorless, odorless, and has little nutritional interest. A pure form of this might be used for cosmetic purposes.
L'huile vierge de noix (Virgin): Made only from high quality nuts, this amber colored oil is rendered by cold pressing. Many times, to intensify the nut flavor, some of the nuts are toasted prior to pressing. This is the highest quality, most flavorful and most nutritious walnut oil you can buy. It's also the most expensive.
L'huile de noix pure (Pure): The oil is a combination of refined and virgin oils. This is the product you'll most often find commercialized and its lower price makes it an attractive alternative to many cooks.
Unrefined oil has the disadvantage of quickly turning rancid. Since this is not an oil you'll be using in large quantities, it is best just to buy a small amount and restock as needed.
Virgin walnut oil is an excellent source of Omega 3 oils and vitamin E. It is recommended as an aid in the fight against heart disease and high cholesterol.
Before opening a bottle, you can store it on a cool and dark pantry shelf. It can be stored like this for up to a year, but do respect the expiration date that should be noted on the bottle.
Once you have opened the oil, you must keep it in the refrigerator between uses (it will remain liquid). This will extend its shelf life, but eventually it will go rancid in the refrigerator as well. The solution is simple: use it before it turns! It's delicious.
Vegetables and Meat. A small amount can be used in vinaigrette recipes and to dress any number of raw and steamed vegetables as well as grilled meats. Many times, it is preferable to use it in a mixture with other oils, for its taste can be quite dominating.
Pasta. Toss hot pasta with a drizzle of oil and some crumbled blue cheese for a fabulously quick but very tasty dish.
Baking. You can substitute this nut oil for other oils in recipes for cakes, cookies, crepes, etc. Bakers also like to grease their molds with this oil to impart a more subtle flavor to their baked goods.
Bread and Cheese. Goat cheese is sometimes preserved in walnut oil flecked with various herbs. Finally, just like olive oil, it can be offered in a small bowl along with bread for dipping.