Vivid Ready

The single most dangerous decision in home preserving. One number decides it, pH 4.6, and getting it wrong is how botulism happens. Read this before any other page in this domain.

Home canning is one of the very best things a household can do with a glut, and it is the only process in this entire app where an ordinary mistake, made by a careful person following sensible-looking advice, can kill someone months later.

That is not a reason to avoid it. It is a reason to get one decision right, every time, before anything else.

The one number

The boundary

pH 4.6.

	pH	Method	Temperature reached
Acid foods	4.6 or below	Water bath canning	100°C
Low-acid foods	Above 4.6	Pressure canning only	116 to 121°C

Below pH 4.6, Clostridium botulinum cannot grow. Above it, in a sealed oxygen-free jar, it can.

That is the whole of it. Every other rule in this domain follows from that line.

DANGER

Low-acid food processed in a boiling water bath is not safe at any duration.

This is not a matter of processing longer. A boiling water canner reaches 100°C and cannot exceed it, however long you leave it. C. botulinum spores survive boiling water indefinitely. Only a pressure canner reaches the 116 to 121°C that destroys them.

So there is no such thing as "water bath the green beans for a really long time". Three hours in a boiling water bath is not safer than one hour; both leave viable spores in a sealed, oxygen-free, low-acid jar, which is the precise environment the organism needs.

The resulting toxin is one of the most poisonous substances known. It is odourless and tasteless. The jar can look, smell and taste completely normal.

If you have no pressure canner, do not can low-acid food. Freeze it, dry it, ferment it, pickle it in vinegar, or salt it. All of those are on other pages in this domain and all of them are safe. Canning it in a water bath is not an acceptable substitute and never becomes one.

Why boiling is not enough

Worth understanding rather than memorising, because understanding is what stops you improvising badly later.

Clostridium botulinum is a bacterium that lives in soil almost everywhere, including British garden soil. It is harmless to eat in ordinary circumstances; you have almost certainly eaten it many times.

It forms spores, which are dormant, armoured, and remarkably heat-resistant. Boiling does not kill them.

The spores only become a problem when they find all four of these at once:

No oxygen. A sealed jar.
Low acid. Above pH 4.6.
Moisture.
Time at moderate temperature. Weeks in a cupboard.

A sealed jar of low-acid food in a larder is a purpose-built incubator for it. Under those conditions the spores germinate, grow, and produce botulinum toxin.

One distinction worth having clearly, because it is widely muddled:

The spores survive boiling. Only pressure canning at 116°C or above destroys them.
The toxin, once produced, is comparatively fragile and is destroyed by boiling for 10 minutes (plus a minute per 1,000 ft of altitude).

That second fact is why the standard advice for a suspect jar of home-canned low-acid food is to boil the contents hard for 10 minutes before even considering it. It is emphatically not a licence to water-bath low-acid food and boil it later: you would be relying on remembering, every time, forever, including the time someone else opens the jar.

Which foods are which

The rule of thumb that catches most cases: if it grew in the ground or had a face, it is low-acid. Fruit is the main exception on the plant side.

The things that move food across the line

Several ordinary, well-meant kitchen decisions push an acid food over pH 4.6, and this is where careful people come unstuck.

DANGER

Tomatoes are the classic trap. Modern tomato varieties hover right around pH 4.6, and many are above it. They were safely water-bathed for generations because older varieties were more acidic.

Tomatoes must have added acid to be water-bath safe: bottled lemon juice or citric acid, at the rate given in a tested recipe. Bottled lemon juice specifically, not fresh, because its acidity is standardised and a fresh lemon's is not.

Other ways food crosses the line without anyone noticing:

Adding onions, garlic, peppers or herbs to a tomato sauce. All are low-acid. A tomato sauce with onions and garlic in it is no longer a water-bath food unless the recipe was tested with them in.
Adding oil. Oil protects organisms from heat and creates oxygen-free pockets. Garlic or herbs in oil at room temperature is a well-documented botulism route.
Reducing the vinegar in a pickle recipe because it tastes too sharp. The vinegar is not seasoning, it is the preservative and the safety mechanism.
Adding flour, cornflour, rice, pasta or barley to thicken. Starch insulates and slows heat penetration to the centre of the jar, so the tested time no longer applies.
Packing jars more densely than the recipe says, for the same reason.
Scaling a recipe up into a bigger jar. Process time depends on jar size, because heat has further to travel.

Why this page will not give you process times

A deliberate decision, and worth explaining rather than leaving you to wonder.

Process times are specific to the food, the jar size, the pack method (raw or hot), the canner type, and your altitude. They come from laboratory heat-penetration studies, not from judgement. There is no way to derive them, sense-check them, or safely interpolate between them.

This app will not print a table of process times that it cannot verify in full, because a half-remembered or approximated canning time is worse than no table at all: it looks authoritative and it is the exact failure mode this whole domain exists to prevent.

Use tested tables. The National Center for Home Food Preservation (NCHFP, University of Georgia) is the standard reference and is freely available. The Ball Blue Book and the USDA Complete Guide to Home Canning are the other standards. Follow one of them exactly.

The UK situation

Worth knowing, because most of the good information you will find is American and written for a different context.

Pressure canning is uncommon in Britain. The British preserving tradition went down the jam, chutney, pickle and bottled-fruit route, all of which are acid foods and all of which are water-bath safe. That is why your grandmother's methods were sound and why they do not extend to vegetables and meat.

Consequences for a UK household:

There is no British domestic pressure canning standard to substitute for the NCHFP tables. Use the American ones; the physics is not national.
Pressure canners are harder to buy here than in the US, and a UK pressure cooker is not the same thing. A canner is larger, takes tall jars upright, and holds a calibrated pressure. Many domestic pressure cookers cannot hold a steady 10 to 15 PSI and are not tall enough for jars.
The FSA's guidance is to follow tested recipes from reliable sources, which is the same answer arrived at from a different direction.
Altitude is rarely an issue. Almost all British households are below 1,000 feet, so the sea-level column usually applies. Check yours if you are in upland Wales, the Pennines or the Highlands.
Dial gauges should be tested annually. In the US, county extension offices do this. In the UK there is no equivalent service, which is a real argument for buying a weighted gauge canner instead: a weight cannot drift out of calibration.

The next pages in this domain cover water bath canning and pressure canning in detail. Both assume you have already made the decision on this page, correctly.