Za'atar as a prepared condiment is generally made with ground dried thyme, oregano, marjoram, or some combination thereof, mixed with toasted sesame seeds, and salt, though other spices such as sumac might also be added. Some commercial varieties also include roasted flour. Traditionally, housewives throughout the Fertile Crescent, Iraq, and the Arabian Peninsula made their own variations of za'atar, which was unknown in North Africa. In Morocco, za'atar mix consumption is sometimes seen as a trait of families with Andalusian roots, such as many inhabitants of Fez. Recipes for such spice mixtures were often kept secret, and not even shared with daughters and other relatives. This general practice is cited by Western observers of Middle Eastern and North African culinary cultures as one reason for their difficulties in determining the names of the different spices used. Written history lacks an early definitive reference to za'atar as a spice mixture, though unidentified terms in the Yale Babylonian Collection may be references to spice blends.