Fermentation and pickling: what is the difference?

A cucumber in a jar does not tell you how it was made. “Pickled” can describe a food made with vinegar or one that became acidic through fermentation. The method matters more than the jar's appearance.

Where does the acid come from?

That distinction comes from the National Center for Home Food Preservation's classification. Some pickle recipes include more than one stage, so read the complete method rather than guessing from the name. NCHFP: General information on pickling

Time follows the method

Sauerkraut develops over weeks; the recipe's temperature range affects how long fermentation takes. It is not the same operation as pouring vinegar over cabbage. NCHFP: Sauerkraut recipe

A quick pickle does not become a fermented recipe simply because it sits for longer. Nor should a vinegar recipe be converted into a ferment by leaving the vinegar out. Use a tested recipe for the food and process you want.

Vinegar is itself a fermented ingredient

Here is the useful twist: vinegar can be made through microbial activity. Acetic acid bacteria use oxygen to convert alcohol into acid. Adding that finished vinegar to a vegetable makes a vinegar pickle; it does not mean the vegetable went through that fermentation. NC State Extension: Vinegar making

Sour does not mean ready for the cupboard

Acidity, proportions, processing and storage belong to a complete preservation method. Keep the vinegar strength and ingredient proportions specified by a tested canning recipe. Home-made vinegar with unknown acidity is unsuitable for improvising a shelf-stable pickle. NCHFP: General information on pickling

Refrigerator storage and canning are different finishing choices. Decide which one the recipe is written for before starting, and follow its instructions.

Fermentation also goes beyond pickles

Yogurt begins with milk and a bacterial starter; sourdough brings bacteria and yeasts into bread making. Browse the six fermentation families to see how different their ingredients and routines can be. University of Illinois Extension: Making yogurt at home University of Minnesota Extension: Building community with sourdough