Filet of Sea Bass With Avocado, Mango Juice and Spicy Paprika

When a chef asks his new saucier, “Is that properly seasoned?” he invariably means, “Has it been salted?” It’s true that salt is a cook’s most important seasoning. But once you’ve mastered it, it’s important to learn how to season with other things as well. Vinegars, citrus juices, yogurt and various spices are all effective tools that can extend any cook’s reach.

As it is with salt, the goal is simple: to bring a sauce, a piece of fish, a soup to the peak of its flavor. And as with salt, you shouldn’t taste the seasoning; you should only recognize its effect.

Next time you make a rich soup--cream of broccoli, say, or cream of mushroom--taste a spoonful plain, then taste a spoonful with a drop of lemon juice in it. The soup with a drop of lemon juice will taste brighter. The various flavors should be more distinctive and have clear edges, as in a photograph brought into focus.

This same principle holds in many situations, whether it is adding vinegar to a pasta sauce, lemon juice to a butter sauce or lime juice to berries, melon or sweet corn.

There are other ways to season without salt as well. Various powders--curry powder, for instance, or powdered citrus zest--can be similarly effective. We pair a robust piece of sauteed fish with sweet mango and tart yuzu juice, which is like a strong lemon juice. We dust the fish after it has cooked with a mild chile powder made from roasted and ground Anaheim peppers. This heightens the flavor of the fish and adds a spicy counterpoint to the sweet and sour elements.

Try brushing a piece of fish with yogurt, letting it sit for a half hour and then gently poaching it in a court bouillon--a quick stock of water and white wine with some carrots, onions and thyme. The yogurt will melt into the court bouillon, adding acidity, and it will have flavored the fish. When the fish is cooked, remove it from the pan, strain the liquid, reduce it slightly, season with salt and swirl in a teaspoon of butter; you’ll have a delicious sauce.

Even flavors more delicate than fish can be enhanced by spices we normally think of as quite powerful. A puree of fava beans as a soup or a sauce, for instance, can be elevated by a pinch of curry powder. These are not rote acts, as salting is. These are choices the cook must make. This kind of seasoning asks the cook to think: “Here are some magnificent green beans, cooked tender in salted water, shocked in ice water. Will they be best reheated in a little sweet butter with lemon juice sprinkled on at the last minute? Or gently sauteed in olive oil and dusted with cumin powder?”

The answer depends on what else is being served at that meal, on what the weather is like and on the mood of the cook. With this kind of seasoning, you have to get involved. You must think for yourself and decide, and this enriches and deepens the act of cooking.

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Keller is chef at the French Laundry in the Napa Valley. Ruhlman is author of “Soul of a Chef” (Viking, $26.95). They are co-authors of “The French Laundry Cookbook” (Artisn, $50). Previous columns by them can be found on The Times’ Web site at: http://www.latimes.com/keller.