yogurt is a fermented milk product obtained through the action of certain bacteria. The prehistoric spread of dairying across an area extending from the Balkans to the Indian subcontinent and the western fringes of China went hand in hand with the spread of milk soured to produce what we now call by the Turkish name yogurt. Throughout these regions, hot temperatures during summer milking season have favored the action of particular lactic acid bacteria known as “thermophilic” because they act best at warm temperatures (between about 105° and 115°F, or 40° to 46°C). Such organisms rapidly colonize milk exposed to the open air, fermenting most of the lactose (milk sugar) to lactic acid and other flavorful byproducts. The result is a creamy, refreshingly tart substance useful for both sweet and savory purposes.