The Turkish fermented millet drink traditionally served in winter is Boza. It is a thick, sweet-tart malt beverage made by fermenting cereal grains, especially millet in Turkey.
Boza is one of the oldest beverages associated with Turkic food traditions. Written evidence for an earlier form appears in the 11th-century Middle Turkic dictionary Dīwān Lughāt al-Turk, while the drink later became widespread across the Ottoman world, the Balkans, the Caucasus, and Central Asia.
In Istanbul, boza became especially associated with Vefa. The famous Vefa Bozacısı shop was founded in 1876, and its thick, sweet, relatively low-alcohol style helped define the modern Turkish version. Boza is often served cool or at room temperature, commonly with roasted chickpeas and cinnamon.
Winter is traditional because boza spoils more quickly in heat and historically was not sold during hot summers. It contains a small amount of alcohol from fermentation, often around 1 percent, so it is not the same as salep, a hot thickened orchid-root drink. Ayran is yogurt-based, while şıra is generally an unfermented grape beverage.