Fermented or pickled?

The one distinction everything else follows from

Where did the acid come from?

In a ferment, the acid is made inside the jar. Bacteria already living on the vegetable eat its sugars and produce lactic acid, and the food gradually becomes too acidic for anything else to grow. Nothing sour was added; the sourness was manufactured on the spot, by organisms, over days or weeks.

In a pickle, the acid arrives from outside. Vinegar — already acidic, already made somewhere else by a completely separate process — is poured over the vegetable, and the jar is hostile from the first minute. No microbial community lives in it and nothing needs to happen over time.

Everything below is a consequence of that.

The four jars, side by side

Fermented — sauerkraut, kimchi, ogórki kiszone

Salt and time. Sour from lactic acid: soft, round, yoghurty. Complex and savoury. Contains live cultures unless pasteurised. Keeps for months refrigerated. Texture stays crisp if made well.

Vinegar-pickled — pickled onions, cornichons, piccalilli

Vinegar poured over, usually with spice and sugar. Sour from acetic acid: sharp, volatile, nose-tingling. Simpler, brighter. No live cultures. Keeps a long time. Texture usually firm, sometimes squeaky.

Quick or refrigerator pickle

Vinegar, water, sugar and salt over raw vegetables, eaten within days. Crisp, fresh, mildly sour. No fermentation, no long keeping. A garnish rather than a preserve.

Shelf-stable jarred pickle

Acidified and then heat-processed so it keeps unrefrigerated. Softer than the others, because heat cooks it. Definitively no live cultures, whichever way it was acidified.

Why they taste so different

Lactic acid and acetic acid are different molecules and taste different. Lactic acid is not volatile, so it does not reach your nose — it reads as a soft, rounded sourness, the sourness of yoghurt and of good sourdough. Acetic acid is volatile, so it arrives in the nose before the mouth and reads as sharp and pungent.

But the bigger difference is everything besides the acid. A ferment has had a population of microorganisms living in it for weeks, and they have produced amino acids, aromatic compounds and small amounts of other acids as they went. That is why sauerkraut tastes savoury and layered in a way pickled cabbage never does. A vinegar pickle tastes of the vegetable, the vinegar and the spices you added, and nothing else, because nothing else happened.

Neither is better. They are different tools: a ferment brings depth and savouriness, a pickle brings clean sharpness and lets the spice through.

Which to reach for

• Want savoury depth to season a dish? Ferment. Kimchi in fried rice, sauerkraut with pork, brine in a dressing.
• Want a sharp counterpoint on a plate? Pickle. Cornichons with pâté, pickled onion in a taco, dill pickles in a burger.
• Want something in half an hour? Quick pickle. Nothing else is that fast.
• Want live cultures? Ferment, unpasteurised, from the chilled cabinet — and do not cook it if that is why you bought it.
• Want it to keep in a cupboard for a year? A properly processed shelf-stable jar, made to a tested recipe from a food safety authority.
• Want the vegetable to still taste of itself? Quick pickle with a mild vinegar, or a short ferment.

The confusing middle ground

Several familiar foods sit awkwardly across the line, and the labels do not help.

Traditional dill pickles are fermented. Most supermarket dill pickles are vinegar pickles made to taste like the fermented ones. Both are sold as "pickles" and they are not the same food — the ingredient list tells you: vinegar in the list means a pickle, salt and water alone means a ferment.

Real sourdough is fermented; bread made with yoghurt or vinegar for flavour is not. Salami is fermented; a vinegar-cured meat is not. Soy sauce, miso, fish sauce, vinegar itself, yoghurt, cheese and cocoa are all fermented foods people do not think of as such.

And a food can be both. Some pickles are fermented first and then finished in vinegar, and some commercial ferments are pasteurised, which kills the cultures but leaves the flavour a ferment produced.

FoodHQ does not publish salt percentages, pH figures or keeping times for home preserving. Those are safety numbers, they are set by a food safety authority rather than by a cookery writer, and the right ones depend on what you are fermenting and where you are. In the UK the Food Standards Agency is the authority — use a recipe from them or from another body with the same standing, and treat this page as the explanation of why that recipe is shaped the way it is.

Common questions