Here’s what you need to know when shopping for sourdough bread so you always buy the genuine thing. Sourdough StarterA sourdough starter is essential for making sourdough bread. A sourdough starter is a live culture that requires care to maintain its viability, allowing you to produce sourdough bread. Sourdough starter is a slow leavener that ferments the dough, which is what makes sourdough bread healthier. Note that while all true sourdough bread is slow fermented, not all slow-fermented bread is sourdough.