Çortan / Keşk (Dried Yogurt Balls)
Çortan (also called keş/keşk in Kurdish areas of Turkey, kashk in Iran/Iraq, qurut/kurut among nomads) is a way of preserving yogurt for the winter and for travel. It is a defining ingredient in many Kurdish village soups and stews, dissolved in water and added near the end of cooking for sourness and body.
Method
Blend the sour yogurt until smooth, then boil it and strain. (Traditionally, butter is first separated from the buttermilk in a goatskin churn, and the remaining curds are boiled.)
Leave the strained mixture to ferment in a warm place for several days, then strain off the moisture to obtain a thick curd (suzma / strained yogurt).
Blend the thick curd with salt to taste; add ground red pepper or dried herbs if desired.
Roll the salted curd into walnut-sized balls (or shape into strips or chunks). Smaller balls dry faster.
Place the balls on a tray and dry them in the sun for several days until completely hard and shelf-stable.
To use: crumble or grind the dried balls and dissolve in water to make a paste. Use to thicken and sour soups and stews, or stir into meat, rice and vegetable dishes for a tangy, savory depth. Store dried in a cool dry place, refrigerator, or freezer.