Ingredient

Walnut oil

Walnut oil is intensely nutty, faintly bitter and one of the best finishing oils there is. It is also among the most fragile: it goes rancid faster than almost any other oil and it turns unpleasantly bitter when heated. Both facts limit it to one job, which it does superbly.

Why it cannot be cooked with

Walnut oil is very high in polyunsaturated fat, which makes it both prone to oxidation in the bottle and unstable in a pan. Heated, it develops a harsh bitterness quickly, and the delicate roasted-nut aroma that justifies the price disappears entirely.

The same instability means it deteriorates faster in storage than any oil except perhaps flaxseed. A bottle left open in a warm kitchen can turn within weeks.

The answer to both is the same: buy small bottles, keep it in the fridge, and use it cold.

Buying and keeping it

Toasted or roasted

Made from lightly roasted nuts. Deeper, more aromatic, and the one worth buying. Usually labelled.

Cold-pressed unroasted

Milder and greener. Pleasant and less distinctive.

Bottle size

Small. This is a finishing oil used a teaspoon at a time.

Storage

In the fridge once opened, always. It will cloud and thicken when cold and clears within minutes at room temperature.

Shelf life

Short. Smell it before each use — rancid nut oil is unmistakable and ruins whatever it touches.

What to dress with it

• Bitter leaves — chicory, endive, radicchio, watercress — where the nuttiness balances the bitterness.
• With walnuts themselves, in a salad with blue cheese and pear or apple. The reinforcement works.
• Over cooked beetroot, which is a classic pairing and a very good one.
• On green beans or purple sprouting broccoli, warm, just before serving.
• In a dressing with sherry vinegar and a little mustard, in about a one-to-three ratio with a neutral oil so it does not dominate.
• Over a soft cheese — goat's cheese, ricotta — with honey and black pepper.
• Stirred into a warm lentil or grain salad off the heat.

Making a walnut oil dressing

The oil is strong and expensive, so it is usually blended rather than used alone.

1. Start with the acid: sherry vinegar, red wine vinegar or lemon juice in a bowl.
2. Add a small spoonful of Dijon mustard and a pinch of salt, and whisk to dissolve the salt.
3. Whisk in a neutral oil first — rapeseed or a mild olive oil — to build the emulsion.
4. Finish with the walnut oil, roughly a quarter to a third of the total fat. Whisk it in gently at the end.
5. Taste and adjust. Walnut oil reads as slightly bitter, so it often wants a little more salt or a pinch of sugar.
6. Dress the salad immediately before serving. Nut oil dressings dull on standing.

Common questions