دوغ

When butter forms in a churn, it separates from a thin liquid: buttermilk, or in Persian, doogh. The word derives from the Persian verb doshidan, to milk or to churn, and in the earliest Persian agricultural vocabulary, doogh designated the byproduct of butter-making, which was soured and mixed with water to produce a drink. Sassanid-era Persian medical texts of the 5th and 6th centuries CE recommend it as a cooling drink in summer, a treatment for fever, and an aid to digestion. The drink was already old when those physicians described it.

The practice of mixing yogurt with water and salt predates the Islamic conquest of Persia in the 7th century, but the word doogh survived the transition and was borrowed into neighboring languages. Arabic adopted a related form; Ottoman Turkish used it in medical contexts. By the medieval period, Persian cookbooks such as the 13th-century Karnama fi Babc al-Tabkh described doogh-based preparations for sick patients and healthy diners alike, requiring salt, dried mint, and cold water from a well or spring.

In modern Iran, doogh divides into two main varieties: the flat, domestic version mixed at home from yogurt and water, and the carbonated commercial version introduced in the 20th century. The Kalleh dairy company began producing carbonated doogh in the 1980s and it became the dominant commercial form. Dried mint and sometimes dried Persian cucumber are added, and the drink arrives in restaurants alongside kebab the way a soft drink accompanies a fast-food meal elsewhere.

The word entered English through culinary travel writing and Persian restaurant culture. Early 21st-century food journalists writing about Tehran or Persian diaspora kitchens in London and Los Angeles used doogh as the standard transliteration, following the convention that romanizes the Persian long vowel as oo. The drink is close cousins with Turkish ayran and Armenian tan, all descending from the same pastoral practice of stretching fermented dairy with water and salt.