Pickles are simply fermented cucumbers. Fermentation is the process of allowing bacteria to grow on the cucumbers. This bacteria does not harm the cucumber, it merely digests the cucumber’s sugar and converts it into lactic acid. This changes the flavor of the cucumber and produces the sour taste that is characteristic of pickles. Due to the high lactic acid content, the pickles have an indefinite shelf life, even when left unrefrigerated for long periods of time.