Cured Egg Yolks: The Umami Ingredient That Grates Like Cheese

A fresh yolk is roughly half water. Bury it in salt, and osmosis begins pulling that water out into the surrounding crystals while salt gradually moves the other way.

As water leaves, the proteins and fats that remain are pressed closer together. Over several days the yolk stops behaving like a liquid and sets into something dense and sliceable, with a texture between a soft sweet and a firm cheese.

The flavour concentrates alongside the texture. Whatever savoury character the yolk had is now packed into a much smaller volume, which is why a light grating goes so far.

Pure salt cures fastest and gives the most savoury result. A common variation is two parts salt to one part sugar, which draws water out slightly more gently and softens the saltiness with a faint sweetness.

Fine salt makes closer contact with the yolk than coarse crystals and gives a more even cure. The mixture must fully surround each yolk — any exposed surface will dry unevenly or take on odours from the fridge.

Four days gives a softer, more spreadable yolk; seven gives one firm enough to grate cleanly. Beyond that it becomes hard and intensely salty.

Once the yolks are firm, rinse them briefly in cool water to remove the crust of salt, then pat them dry. They will look translucent and amber, like small jewels.

A day or two uncovered on a wire rack in the fridge dries the surface and firms them further. Some cooks dry them in a very low oven or dehydrator, which is faster but easier to overdo.

Wrapped and refrigerated, they keep for around a month. Discard any yolk that develops an off smell, a slimy surface or visible mould.

Treat cured yolk as a finishing ingredient in the same way you would treat a hard aged cheese: grated at the table, in small quantities, over something warm.

It is superb over pasta, risotto, buttered toast, roasted vegetables, mushrooms, soups, salads and steamed greens. The warmth releases the aroma and the salt seasons the dish at the same time.

It is not a protein serving, and it is not a substitute for an egg in cooking. Think seasoning, not ingredient.

Salt curing of egg yolks appears in Chinese cooking, where salted duck eggs are a long-standing tradition, and in Italian kitchens where cured yolks are grated much like bottarga or hard cheese.

The underlying principle is the same one behind salt cod, cured fish roe, preserved lemons and country hams: remove enough water and add enough salt, and food that would otherwise spoil becomes stable and intensely flavoured.

Learning it on egg yolks is a good way to understand the wider technique on a small, cheap and forgiving scale.

This is a cure, not a cook. Raw eggs can carry salmonella, so use very fresh eggs from a reputable source, wash your hands and equipment, and keep the container refrigerated throughout.

People who are pregnant, elderly, very young or immunocompromised should be especially cautious with any preparation using uncooked eggs, and may prefer to use pasteurised eggs or avoid the recipe entirely.

The finished yolks are extremely salty. Anyone monitoring sodium intake should account for that, even in the small amounts used.

This recipe contains egg and is not suitable for anyone with an egg allergy.

Salt removes water, water removal firms the yolk, and firmness turns it into a grating ingredient. It is a week of doing almost nothing for a jar of something you will use constantly.