Backslopping

Backslopping is the practice of using a spoonful of liquid or a portion of a finished ferment to inoculate a new batch, rather than starting completely from scratch each time. It is a traditional technique used across many fermented foods, including sourdough, yogurt, kombucha, and some vegetable ferments, and it works because the finished batch already contains an active, established population of the right microorganisms.

The main advantage of backslopping is consistency, since a culture that has already proven itself in your kitchen tends to behave predictably in the next batch, often fermenting a bit faster than starting fresh because the microbial population does not need to build up from nothing. It also reduces reliance on buying new starter cultures for every single batch.

The main risk is that backslopping repeatedly from the same lineage can gradually shift the balance of microorganisms over many generations, sometimes changing flavor over time, and any contamination introduced at one stage can carry forward into future batches. Many fermenters keep a portion of a particularly good batch aside specifically for this purpose, and switch to a fresh starter occasionally if flavor or activity starts to drift.