Sourdough starters are wild yeast cultures that require regular feeding of flour and water to stay active. They have been used for centuries to leaven bread and were considered valuable possessions. There are a few ways to obtain or create a starter, including asking friends, purchasing dried starters, or capturing wild yeasts from the air. Starters must be cared for by regular feedings and can be stored in the refrigerator, freezer, or dried. With occasional feedings, starters can last a long time but may need resuscitation if neglected for many months.