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Home canning and botulism

Also called bottling; preserving in jars

Why low-acid food in sealed jars needs a tested process, not a household one.

What it is

High-acid foods can be safely processed in a boiling water bath. Low-acid foods — most vegetables, meats, fish, and mixtures like soups — require pressure canning to reach temperatures a boiling pan cannot. Follow a tested, published recipe exactly.

Why it works

Clostridium botulinum spores survive boiling and germinate in exactly the conditions a sealed jar of low-acid food provides: no oxygen, moisture, room temperature. The toxin they produce is among the most dangerous known and is tasteless and odourless. Acidity below about pH 4.6 prevents growth, which is the dividing line between the two methods.

When to use it

Preserving vegetables, beans, meat, fish, pesto, garlic or chilli in oil, and any mixed dish intended to be shelf-stable.

What goes wrong

Adapting a tested recipe by reducing vinegar or salt; water-bath canning vegetables; sealing garlic or herbs in oil and storing them at room temperature; judging safety by whether the lid sealed.

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