Smen (from Arabic: سمن or سمنة also called sman, semn, semneh, or sminn) is salted fermented butter, an important cooking ingredient widely used in Moroccan and Algerian cuisine and most common in other North African and Middle Eastern cuisines. It is produced using the butter made from the milk of sheep, goats or a combination of the two. The butter is brought to boiling point for about 15 minutes, then skimmed, strained into a ceramic jar called a khabia, and salted before it curdles. Thyme is often added to it to provide a yeast and enzyme starter. Other plants or fruits can be used. The result is then aged, often in sealed containers. It is then traditionally buried in the ground for temperature stability purposes, just like cheese is left to mature in underground caves because they have cooler and more stable temperatures.
It is similar to ghee and niter kibbeh, but has a characteristically strong, rancid, and cheesy taste and smell. Matured smen is very similar in taste to blue cheese because likewise it is a high-fat form of cheese. The older the smen, the stronger—and more valued—it becomes. Smen is traditionally used mainly in the preparation of couscous and trid, as well as of tagines and kdras, although it is becoming increasingly difficult to find due to its increasing replacement by peanut oil, a non-native culinary element introduced from Senegal and other West African countries.
Smen made during winter is believed to be more fragrant than those made during a warmer season. In constant warm weather, closer to the temperature where butter becomes liquid, smen matures very slowly. In lower temperatures, one month is considered an acceptable time to start using the smen in cooking, although its flavour will not be strong. In a constant warm weather, like in equatorial countries, it can take up to four months to develop the equivalent amount of flavour.
Smen holds great cultural significance, particularly as an indicator of familial wealth. As such it will often be used as a token of honor for esteemed visitors to a household, akin to other cultures' customs such as using the "fine china" or serving an especially prized wine.
Berber farmers in southern Morocco will sometimes bury a sealed vessel of smen on the day of a daughter's birth, aging it until it is unearthed and used to season the food served on that daughter's wedding.