You probably won't find walnut oil.
And this is a pity, because it can be very good.
"Why walnut oil? I thought Italy is the land of the Olive Tree," I hear you say.
Much of Italy is the land of the olive tree; it grows very well in the south, with trees so large I mistook them for scrub oaks the first time I saw them, and though the trees are smaller further north, they do grow as far as Liguria, Tuscany and Umbria, and produce spellbinding oils.
Olive trees don't do so well north of the Apennines, however: Though the Romans did try to introduce them, they succeeded in growing them only in well-protected spots, and never produced enough olives to make olive oil production a viable activity. As a result olive oil is conspicuously absent from the traditional cooking of northern Italy -- people used animal fats, or, if they could afford it, butter. And had to come up with something else to use as a condiment, for example over salads or soups.
Walnut oil is a logical choice: walnut trees grow quite well in the colder northern climates, and the oil from the nuts is delicately walnut-flavored, rich in minerals, and easy on the digestion.
In Northern Piemonte, because of its isolation, walnut oil was especially prized, and indeed stands of walnut trees were one of the characteristic features of the landscape, while the crop was important enough that, in the Middle Ages, towns punished those who snuck into groves to pick up fallen walnuts, and also imposed transport duties upon both walnuts and walnut oils.
The walnut harvest took place in autumn: People gathered together to pick the nuts, which were then dried, shelled, and ground; the resultant nut flour was heated, and then pressed to extract the oil. It was a communal activity, with families or neighborhoods helping each other work through their stands of trees.
And, as is often the case with communal activities, walnut oil production played a social function, helping cement both families and neighborhoods. Unfortunately, the oil does have several drawbacks, the foremost being the high cost of making it -- even if people weren't paying for it, they were still putting in the time. The other two are related more directly to the oil:
- Walnut oil has a very low smoke point, which means that it cannot be used for frying, and is not too suitable for cooking either.
- Walnut oil lacks the antioxidants one finds in olive oil, and as a result will keep a year at most before becoming rancid in an unopened container, and for a month or two if kept in a cool dark place after the container is opened.
But it never vanished completely, and now there is renewed interest in it on the part of lovers of traditional foods and those interested in preserving traditional ways of life; in particular, the Province of Biella is trying to revive it, and held a presentation dedicated to walnut oil at Slowfood's Salone del Gusto.
Before we get to the recipes, a couple of words about purchasing walnut oil: Since it is perishable, you should buy small amounts, and check the container before purchasing it to make certain that it's not more than a year old.
If you live in Europe, the Province of Biella was pouring an oil made by a farm called Oro Di Berta.
If you are elsewhere, check a good delicatessen or health food place. Or check the web; Google turned up a number of suppliers, in North America and elsewhere. One thing to be wary of is oils that are overly cheap; since making walnut oil is a labor-intensive process, something that is overly cheap may have been made by cutting corners.
Now You've Got Some Walnut Oil: What To Do With It?