Pickling is one of the oldest and most useful preserving methods, and it has one safety-critical variable. Everything else on this page is flavour and texture.
That variable is acidity, and unlike sugar in jam, where a failure produces visible mould, a failure here can be invisible. That is the reason for the emphasis below.
How pickling preserves
Acid stops things growing. Below a pH of 4.6, Clostridium botulinum cannot grow and cannot produce its toxin, and most other spoilage organisms are inhibited too.
That threshold is the whole of food preserving safety. It is why some foods can be water bath processed and others must be pressure canned, and it is set out fully on water bath or pressure: choosing correctly. Read that page before this one if you have not.
A pickle works by making a low-acid food into a high-acid one, by surrounding it with enough vinegar. If there is not enough vinegar, or it has been diluted by water from the vegetables, the jar may sit above the threshold and the food is then no safer than an untreated low-acid food in a sealed jar.
Pickling is not fermenting
Two different methods, often confused, with different mechanisms.
Fermenting is covered separately. See ferment vegetables, which is a different process with its own rules.
Do not judge one by the other's signs. Bubbling in a ferment is the process working; bubbling in a vinegar pickle means something is growing that should not be.
The vinegar
At least 5% acetic acid. Commercial vinegars state their acidity on the label, and most malt, white wine, cider and distilled vinegars sold for pickling are 5% or above.
Check the bottle. Some table vinegars are weaker, and some are sold specifically as pickling vinegar at a higher strength.
Which vinegar for flavour:
- Malt is the traditional British pickling vinegar. Strong, dark, and it dominates.
- Distilled or spirit vinegar is clear and neutral, and keeps the colour of what is in it.
- Cider vinegar is milder and fruity.
- Wine vinegar is good and more expensive.
Spiced vinegar is made by steeping whole spices in the vinegar, warm or cold, and straining. Whole spices rather than ground, which clouds it.
Salting first
The step that decides whether the pickle is crisp or limp, and it is also a safety step.
Watery vegetables release liquid into the jar, and that liquid dilutes the vinegar. Drawing it out first keeps the vinegar at the strength you intended.
- Dry salting: layer sliced vegetables with salt, leave for several hours or overnight, then rinse and drain thoroughly. Used for cucumber, courgette, marrow.
- Brining: submerge in a salt solution overnight, then drain. Used for onions, shallots, cauliflower, beans.
- Rinse and drain properly, or the result is inedibly salty.
- Pat dry before packing.
It also firms the texture, which is why shop pickles are crisp and hurried home ones are not.
Equipment and jars
- Wash jars, then sterilise, and have them hot when filling. Oven at around 120 degrees for fifteen minutes, or a hot dishwasher cycle timed to finish as you need them.
- Check every rim for chips.
- New lids for anything relying on a sealing compound.
Hot pack and cold pack
Cold pack: raw prepared vegetables packed into the jar and covered with hot vinegar. Keeps more crunch. Used for onions, gherkins, beetroot.
Hot pack: vegetables cooked briefly in the vinegar and packed hot. Better penetration, longer keeping, softer texture.
Either way:
- Pack the jars firmly but not crushed, leaving the headspace the recipe states.
- Cover completely with vinegar. Anything above the surface will spoil, and this is the commonest visible failure.
- Remove air bubbles by running a plastic or wooden implement down the inside.
- Wipe the rim clean before the lid goes on. A trace of liquid on the rim prevents a seal.
- Seal, label with the contents and the date.
- Water bath process where the recipe calls for it, which is what makes a jar reliably shelf stable. See water bath canning, jar to seal.
- Mature for several weeks before opening. Pickles are harsh when new and improve considerably. Onions want a month or more.
What must not be pickled this way
Anything low in acid, in a recipe that has not been tested for acidity, is not safe for cupboard storage.
Garlic and herbs in oil deserve a specific warning. Low-acid material submerged in oil at room temperature is an oxygen-free environment and a recognised botulism route. Keep such preparations refrigerated and use them within days, or acidify them properly to a tested recipe.
A vegetable in a jar of water is not preserved. It is a low-acid food in an anaerobic container, which is the exact condition this whole domain exists to avoid. See pressure canning, operationally.
Fridge pickles
The safe way to improvise, and it is genuinely useful.
Make anything you like, in any proportions, and keep it in the fridge, eating it within a few weeks. Refrigeration does the preserving and the vinegar does the flavour.
- No processing needed.
- Ready in a day or two.
- Crisp, fresh and bright, better than a matured pickle for many uses.
- Label with the date and treat it as a fresh food.
This is where to experiment. Save the tested recipes and the water bath for the jars that will sit in a cupboard for a year.
Storing and judging
- Cool, dark and dry. Light bleaches the colour and warmth softens the texture.
- Label everything with the date.
- Mature before opening, several weeks at least.
- Refrigerate after opening, and keep everything below the surface of the liquid.
- Most pickles keep a year or more unopened and made properly.
Discard the jar if any of these:
- A bulging or flexing lid, or a seal that has gone.
- Bubbling or fizzing in a vinegar pickle, which is not the same as a ferment.
- Cloudiness that was not there, though note that cloudiness from table salt with anti-caking agent, or from hard water, is harmless and common.
- Mould of any colour, anywhere, including on the underside of the lid.
- A smell that is off, yeasty or unpleasant.
- Anything that was above the liquid.
- Slimy or ropy texture.
Never taste to decide. The full reasoning and the discard procedure are on recognising canning failure, and they apply here without modification.