It’s a bit like making alcohol—it’s made through fermentation, but you want it to be very controlled.

Normally you’d want to sterilize the starting mix first to kill any undesired molds and bacteria, add the fermenting agent that you want (lactic acid producing bacteria in this case) and age it in a sealed container until ready.

If it starts with any contaminants or if any are introduced during fermentation, it’d spoil the batch and make you very sick if ingested.