Starter culture
Japanese: スターター（種菌）
Microorganisms or their cultures added to food to initiate fermentation. Examples include tane-koji (seed koji), yogurt starter, and sourdough levain.
A starter is a microorganism added to initiate fermentation. Seed koji, yogurt starter, bread levain—they take many forms, but the role is the same: providing the initial trigger that says 'let fermentation begin.'
The greatest advantage of using a starter is fermentation stability. By introducing a large population of desired microbes from the outset, you suppress unwanted organisms and reduce quality variation.
On the other hand, there is also wild fermentation, which relies on naturally occurring microbes. Unpredictable, yet capable of producing flavors found nowhere else.