To quote this generation's purveyor of wisdom, the Internet, consider what Artpurveyors.com has to say about walnut oil: "Artists have been using walnut oil since the 5th century and found it to be superior to linseed oil because it yellows and cracks less while being easier to manipulate." Well, artists, forget cracking, yellowing, and manipulation, the cook's canvas is taste. The toasted nut flavor of walnut oil offers a new palate of flavor offerings that will ennoble many late summer treasures.
Walnut oil, from the English walnut, is from the pressing of the fruits of the Juglans regia tree. Regia means "regal nut of Jupiter" and regia or regal because the ancients believed the gods dined on walnuts. And now they are available for us mortals. The origins of the nut are cloudy, but ancient Roman documents credit Persia with being the nut's original homeland. The black walnut, juglans nigra, although a native of North America, is too difficult to hull and seldom seen as an oil.
A good quality walnut oil is topaz in color with a rich nutty taste. Taking short cuts in the production process causes the taste of the oil to vary tremendously. Some producers simply macerate the nuts in vegetable oil. Others do not roast them after grinding. While others, for aesthetic reasons, over filter to give a clear and pristine-look to the product. They all are doing the oil a disservice. Macerating gives little or no flavor to the oil; roasting is necessary for the rich nutty flavor (The label should always read that the nuts have been roasted), and too much filtering extracts too much flavor.
Once opened, all nut oils should be kept in a cool place out of the light or refrigerated to prevent them from becoming rancid. Also, resist the urge to stock up on large quantities of nut oils as they become rancid more quickly than other vegetable oils.
Because California is the world's largest producer of walnuts, Americans are most apt to find California walnut oils on their supermarket shelves. Up until now, the quality has not been up to the standards of the French oils. Fortunately, small companies, such as The California Press in Yountville, California, by studying the French processing methods, have thankfully been able to achieve remarkable flavor success. (California Press (email@example.com) sends out an exceptionally high quality recipe packet). Whether French or American, however, price usually is the determining factor in taste. Using whole nuts or large nut pieces, careful roasting, and proper filtering increases the price to the consumer.
Walnut oil is not a cooking oil; high heat destroys its delicate flavor. Where it does shine is as an ingredient in a salad dressing or a fresh pasta sauce or to give a final fillip to a finished dish. Mixed with a little cream and medium dry sherry, it gives class to a piece of freshly poached salmon or chicken breast. A few toasted walnuts add texture and decoration. A mix of walnut oil, sherry vinegar, a touch of garlic, prepared mustard, and salt makes an excellent dressing for an endive and radicchio salad. Top the salad with a sprinkle of crumbled blue cheese. And for an entrée, use walnut oil in fresh vegetable pasta sauces. Toss steamed fresh garden spinach and chopped shallots with a little walnut oil to put over pasta for the perfect Sunday night supper.