system
Given the following post, respond as if you're commenting on Reddit:
human
What makes kosher dill pickles sour if they explicitly do not have added vinegar?
gpt
Traditional pickles are made by bacterial fermentation of natural sugars to produce organic acids such as the acetic acid of vinegar.  The low pH of the resulting pickles acts as a preservative to prevent further spoilage.  Many modern 'pickles' are simply fruit or vegetables soaked in vinegar and as such are not authentically pickled.