What strength vinegar do I need for pickling?

A pickle keeps because it is too acidic for anything to grow in, not because it is in a jar. The acetic acid percentage on the bottle is therefore a safety specification rather than a flavour note, and it is the one figure worth checking before you start.

Safety

Step by step

1. Read the acetic acid percentage on the bottle.UK vinegars are required to state it. Malt vinegar is typically 5%, distilled malt 5% or higher, cider vinegar usually 5%, and white and red wine vinegars vary from about 5% to 7%. Some speciality and unfiltered vinegars are 4% or less and are not suitable for shelf-stable pickling.
2. Use 5% or above for anything not refrigerated.That includes pickled onions, piccalilli, pickled beetroot, chutney and any jar destined for a cupboard. Below 5%, keep the jar in the fridge and treat it as a short-life item.
3. Do not dilute to soften the taste.Adding water to a tested recipe's vinegar lowers the acidity of the whole jar and is exactly the modification that makes it unsafe. If it is too sharp, add sugar, or use a milder-tasting vinegar of the same strength — cider or white wine rather than malt.
4. Watch the water the vegetables bring with them.Cucumbers, courgettes and marrow are mostly water, and that water dilutes the brine once it is in the jar. This is why recipes tell you to salt those vegetables first and drain them for several hours — the salting step is part of the acidity calculation, not a texture tip.
5. Keep the quantity as written.In a tested chutney or pickle recipe, the vinegar quantity relative to the fruit and vegetables is a safety figure. Reducing it because it smells strong in the pan is the commonest way a chutney ends up mouldy or, worse, unsafe.
6. Use non-reactive equipment.Stainless steel or enamelled pans, plastic or nylon sieves, and vinegar-proof lids. Vinegar strips bare aluminium and copper and eats the coating off a plain metal jam-jar lid, which then corrodes into the pickle and lets the seal go.
7. Know when it is a quick pickle instead.A refrigerator pickle — hot brine of roughly half vinegar and half water poured over vegetables and kept in the fridge — is a different product with different rules. It is fine at lower acidity precisely because the fridge is doing the preserving. It is not shelf-stable, ever.

Tips

• Distilled malt vinegar keeps colours bright; brown malt vinegar makes everything the same shade of brown but tastes traditional in an onion pickle.
• Spiced vinegar made by steeping whole spices in cold vinegar for a month is milder and clearer than boiling the spices in it.
• Do not use a home-made vinegar of unknown strength for a shelf-stable pickle. Fermented cider vinegar from a jar on a windowsill has no measured acidity and could be anything.

Common mistakes

• Using a 4% or unfiltered artisan vinegar for pickled onions — The jar tastes fine and looks fine and simply does not have the acidity to hold a low-acid vegetable safe for a year in a cupboard. Check the percentage or keep the jar in the fridge.
• Topping up a half-used jar of pickles with fresh vegetables and no fresh brine — The original brine has already been diluted by the first batch and partly used up. Adding more low-acid vegetable to it drops the acidity further. Make fresh brine.

Questions people ask