A variety of foods are consumed on Yalda. Shab-e Yaldâ or Shab-e Chelleh is an ancient Iranian festival originally celebrated on the Northern Hemisphere's longest night of the year, that is, on the eve of the Winter Solstice.
Yalda has a history as long as the Mithraism religion. The Mithraists believed that this night is the night of the birth of Mithra, Persian god of light and truth. At the morning of the longest night of the year the Mithra is born from a virgin mother. Following the Iranian calendar reform of 1925, which pegged some seasonal events to specific days of the calendar, Yalda came to be celebrated on the night before and including the first day of the tenth month (Dey). Subject to seasonal drift, this day may sometimes fall a day before or a day after the actual Winter Solstice.
Following the fall of the Sassanid Empire and the subsequent rise of Islam, the religious significance of the event was lost, and like other Zoroastrian festivals, Yalda became a social occasion when family and close friends would get together. Nonetheless, the obligatory serving of fresh fruit during mid-winter is reminiscent of the ancient customs of invoking the divinities to request protection of the winter crop.
The 13th century Iranian poet Sa'di wrote in his Bustan: "The true morning will not come, until the Yalda Night is gone". Yalda Night has been officially added to Iran's List of National Treasures in a special ceremony in 2008.