How is smen (aged Moroccan butter) made?

Smen is the ingredient that divides the room. To a Moroccan grandmother it is liquid gold; to an unprepared visitor it can smell alarmingly like very ripe blue cheese — and both reactions are correct, because smen is essentially butter taken on a long, deliberate journey into ferment. It is one of the oldest preserving tricks in North Africa, born of necessity in a hot climate before refrigeration: a way to keep the goodness of fresh butter for months or years. I first met properly aged smen in a Berber home in the Atlas, where a small jar was treated like a family heirloom — and in a sense it was.

The making starts with fresh butter, traditionally churned from the cream of sheep, goat or cow milk in a goatskin or clay churn. The crucial step is working it with salt: the butter is kneaded firmly, often with a little warm salted water added and pressed out again repeatedly, to drive out every last trace of buttermilk. That buttermilk is what would turn rancid, so removing it is what lets the butter keep. Plenty of salt is worked through as a further preservative. Some families flavour it at this stage, boiling the butter gently with herbs like oregano or thyme and straining it, which both perfumes it and clarifies it.

Then it is sealed away to age, and this is where smen earns its mystique. The salted butter is packed tight into an earthenware jar or pot, sealed so air is kept out, and left in a cool dark place — a cellar, a buried hole in the ground, the corner of a storeroom. In some families a jar is started at the birth of a daughter and opened at her wedding years later. Over those months the butter slowly ferments and transforms, developing the deep, savoury, pungent, almost cheesy aroma that defines it. The longer it ages, the funkier and more prized it becomes.

You never eat smen on its own; it is a seasoning used with a tiny, knowing hand. A small nub stirred into a pot of couscous, melted into a lamb tagine, or sealed into a tanjia adds an umami depth and a faint fermented tang that rounds the whole dish out — the difference between good and unforgettable. It is an acquired love, and I always tell guests not to judge it by the jar but by what it does to the food. Tasting a couscous finished with real aged smen, you finally understand why Moroccan grandmothers guard their jars so fiercely.