Starter
A live culture of microbes kept to begin a new batch of bread, yogurt or another fermented food.
Also: starter culture, mother, levain
In fermentation, a starter is a small amount of active culture added to fresh ingredients to get things going. A sourdough starter is flour and water in which wild yeasts and bacteria live, fed regularly with more flour. A spoonful of yesterday's yogurt sets today's milk. Vinegar, kombucha, cheese and many Asian ferments also rely on starters. Some are kept alive for decades. The word has a second meaning in dining: the first course of a meal.