Saffron is by far the most expensive of all spices. The saffron threads used for flavoring are the bright orange three-pronged stigmata, as well as a portion of the style that comes with it, of a small variety of purple crocus. The facts that they can only be harvested by hand and that it takes around 75,000 flowers to produce 1 pound (455 g) of saffron, explains the high price. Several varieties of this spice grow wild in the Mediterranean area of Europe; however, true cultivated saffron can best be distinguished by its large, loosely hanging stigmata. Saffron has been used since ancient times; it was introduced to northern Europe by the Romans. Later, in the eighth century, the Muslims brought it west to Spain, which today is the largest producer. Saffron is indispensable for making Spanish paella, French bouillabaisse, and Milanese risotto, and it is used to a great extent in Middle Eastern cuisine as well as in a number of European baked specialties, such as the traditional saffron buns and breads. Saffron should always be purchased as threads, as the ground form can be easily adulterated with other yellow to orange foods, such as safflower and marigold petals or ground turmeric. Ground saffron also loses its aroma more quickly. Containers of saffron sold to the foodservice industry are generally 1 ounce (30 g) and are marked with an expiration date. The saffron is still viable well past that date in most cases, provided it has been stored in an airtight container, protected from light.