What genuinely belongs in a boiling water canner

Sources last opened 2026-08-26.

The short version

The guide names them: fruits, pickles, sauerkraut, jams, jellies, marmalades and fruit butters [F-1.1]. Those are acid foods, at or below a pH of 4.6, and boiling water is a sufficient process for them.

Two foods join the list conditionally. Tomatoes and figs sit close enough to the line that some are over it, and they belong in a boiling water canner only after they have been acidified [F-1.5].

Nothing else belongs. Not because plain vegetables, meat, poultry or milk are unusually dangerous, but because they sit above 4.6, and above that line the heat has to do all the work — which boiling water cannot do at any length of time [F-1.2].

The list, and why it is a list of pH rather than a list of foods

Search for what you can water bath and you will find inventories: berries, peaches, apple sauce, pickles, jam. Those inventories are mostly right, and they are right by accident, because they were copied from each other rather than from the thing that decides.

What decides is a pH of 4.6 [F-1.1], and that one number is the whole of the choice between the two machines: water bath or pressure. At or below 4.6 the food is an acid food, which is not the environment the guide lists as one Clostridium botulinum grows in [F-1.4], so the boiling water is only being asked to deal with moulds, yeasts and ordinary bacteria — which it does easily. Above 4.6 there is nothing holding the spores back, so the heat has to destroy them, and that takes 240° to 250°F [F-1.2]. A pot of water at a rolling boil is not near it and cannot be brought near it.

So the useful question about any food is not "have I seen someone water bath this?" It is "what put this food at or below 4.6, and was that quantity tested?"

For a peach, the answer is: it grew that way. For a pickle, the answer is: a tested proportion of 5 percent vinegar [F-2.9]. For a jar of green beans, there is no answer, which is why there is no boiling-water process for them and why they belong in the other hub entirely: pressure canning.

The two foods at the edge

The guide names them in one sentence, and most pages quote only half of it.

Some tomatoes "are now known to have pH values slightly above 4.6", and figs also have pH values slightly above 4.6 [F-1.5]. Both must be acidified with lemon juice or citric acid to be canned as acid foods, and once properly acidified, both can be safely processed in a boiling water canner [F-1.5].

Figs are the forgotten half. If you have been handed fig preserve advice that never mentioned acidification, it was working from half a sentence.

Tomatoes get their own page here, because the tomato question is the one that generates the most confident wrong answers on both sides: tomatoes, the exception the whole niche gets half-right.

The vessel, and the one measurement that matters

You need a pot deep enough to keep at least an inch of briskly boiling water over the tops of the jars for the whole process, a rack to hold them off the bottom, and a lid [F-2.1]. That is the specification in full.

Two details that come from the same part of the guide and are worth having in your head before your first batch, because both are about keeping the process honest rather than about equipment.

For any process longer than 30 minutes, the water should be at least 2 inches above the jar tops rather than one, because a long boil loses water to steam [F-2.2].

And if the boil stops at any point during the process, the guide's instruction is to bring the water back to a vigorous boil and begin the timing over, from the beginning [F-2.5]. Not to add the missing minutes. To restart. That is a blunt rule and it exists because a process that dropped below boiling partway through is not a shortened process, it is an unknown one.

What this page does not decide

It does not give you a time. Once you know your food belongs on this side, the process time comes from a tested recipe for that specific food, in that specific jar size, adjusted for your altitude — and this site publishes none of them, on purpose. NCHFP's own directories are linked below and they are the place to get them.

It does not tell you a finished jar is safe, either. A lid that pulls down proves that a vacuum formed inside the jar. It proves nothing about the temperature the food reached before that happened, which is exactly why jars filled by methods with no process at all still seal.

And it does not settle the mixtures. If what you are canning is a recipe rather than a fruit, the recipe is the finding, and departing from its proportions puts you outside what was tested [F-1.1].

The list, in the guide's own words

Low-acid foods have pH values higher than 4.6. They include red meats, seafood, poultry, milk, and all fresh vegetables except for most tomatoes. Most mixtures of low-acid and acid foods also have pH values above 4.6 unless their recipes include enough lemon juice, citric acid, or vinegar to make them acid foods. Acid foods have a pH of 4.6 or lower. They include fruits, pickles, sauerkraut, jams, jellies, marmalades, and fruit butters.

USDA Complete Guide to Home Canning, 2015 revision, p. 1-8

The link above opens the document itself, so a printed page number leads somewhere. What this document is, and who maintains it.

Opened and read by this site on 2026-08-26.

The second half of that passage is the whole of this page. Fruits, pickles, sauerkraut, jams, jellies, marmalades, fruit butters. That is what a boiling water canner is for.

Notice how the list is built. It is not a list of foods that are easy, or small, or traditional. Four of the seven items are foods that were made acid by a recipe — a pickle, a sauerkraut, a jam with lemon in it. They qualify because of what was done to them, not because of what they started as.

Notice the sentence in the middle, too, because it is the one that catches people. A mixture of low-acid and acid food is above 4.6 unless the recipe contains enough acid to bring it down. A jar of tomatoes with celery and onion in it is not a tomato product. It is a mixture, and the guide puts mixtures on the low-acid side unless a tested recipe says otherwise.

And notice what the passage does not do. It gives no times, no exceptions for careful people, and no room for a food that is "probably acidic enough". It sorts food into two piles and hands each pile a different machine.

What counts as a boiling water canner, which is less than the shops suggest

These canners are made of aluminum or porcelain-covered steel. They have removable perforated racks and fitted lids. The canner must be deep enough so that at least 1 inch of briskly boiling water will be over the tops of jars during processing.

USDA Complete Guide to Home Canning, 2015 revision, p. 1-18

The link above opens the document itself, so a printed page number leads somewhere. What this document is, and who maintains it.

Opened and read by this site on 2026-08-26.

Three requirements, and only one of them is about the pot itself.

A rack, so the jars are off the bottom and water circulates underneath them. A lid, so the water stays at a boil without losing heat to the room. And depth: enough that at least an inch of briskly boiling water covers the lids for the whole process [F-2.1].

That is the entire specification. There is no requirement to buy a vessel with the word "canner" printed on it. A deep stockpot with a rack that fits meets the description; a wide shallow pot does not, however heavy its base, because you cannot get an inch of water over quart jars in it.

What the guide is protecting here is simple. A jar top that breaks the surface during the boil is not being held at the process temperature, and the timed process assumed it was.

The one time empty jars must actually be sterilised

All jams, jellies, and pickled products processed less than 10 minutes should be filled into sterile empty jars.

Empty jars used for vegetables, meats, and fruits to be processed in a pressure canner need not be presterilized. It is also unnecessary to presterilize jars for fruits, tomatoes, and pickled or fermented foods that will be processed 10 minutes or longer in a boiling-water canner.

USDA Complete Guide to Home Canning, 2015 revision, pp. 1-14 to 1-15

The link above opens the document itself, so a printed page number leads somewhere. What this document is, and who maintains it.

Opened and read by this site on 2026-08-26.

This is one rule with a hinge in it, and the hinge is the length of the process.

A short process — under 10 minutes in boiling water — does not itself sterilise the jar, so the jar has to arrive sterile. That is jams, jellies and quick-pickled products with brief schedules [F-2.4].

A process of 10 minutes or longer does the job on the way past, so presterilising is redundant [F-2.4]. Fruits, tomatoes, pickles and ferments with those schedules go into clean, hot jars, not sterilised ones.

Read the second sentence carefully before you decide which case you are in. It says presterilising is unnecessary, not that it is wrong. Nothing goes bad if you sterilise jars you did not need to. The failure runs the other way: a short-process jam into a jar that was merely washed.

And note what the passage does not say. Washing and preheating are not sterilising, and the guide says so in as many words on the same page [F-2.3]. Whether your jars need to be sterile is decided by the process time in the tested recipe you are following, which is where you should be reading it from.

What people ask next

Can I water bath green beans if I add vinegar to the jar?

Adding vinegar is not the same as pickling. Pickling, in the guide's own glossary, is adding enough vinegar or lemon juice to bring a low-acid food to a pH of 4.6 or lower, and properly pickled foods may then be safely heat processed in boiling water [F-1.6]. A tested dilly bean recipe is that. A jar of plain beans with a splash of vinegar in it is not, because nobody has measured what that splash does to that jar. The mechanism is worth understanding in full: what the vinegar is actually doing.

Is a stockpot really acceptable, or is that a corner I am cutting?

It is acceptable if it meets the description: a rack, a fitted lid, and depth enough for an inch of briskly boiling water over the jar tops [F-2.1]. Measure before you commit — stand a jar of the size you plan to use in the pot, add the rack underneath it, and see whether you have the clearance. That is a real check, not a formality. Note also that long processes want more water over the tops than short ones, so read the tested recipe's own instruction before you fill the pot [F-2.2].

Where do salsa, chutney and relish sit?

On whichever side their tested recipe puts them, and you cannot reason your way to the answer from the ingredients. These are mixtures, and the guide's default for a mixture of low-acid and acid food is that it sits above 4.6 unless the recipe contains enough acid to bring it down [F-1.1]. The proportions in a tested salsa are the finding. Change the ratio of peppers to tomatoes and you have left the recipe that was tested.

Does a steam canner count as a boiling water canner?

The same category of food qualifies, but not the same list. A steam canner reaches the temperature of boiling water and no higher, so it is for acid or properly acidified food only, exactly as a boiling water canner is — and it is explicitly not a vessel for low-acid food.

Two limits then cut the list down further. The process time has to be 45 minutes or less including any altitude adjustment, which puts the longer boiling-water processes out of reach entirely [F-6.2]. And it is to be used with recipes approved for half-pint, pint or quart jars [F-6.3], so the half-gallon case above does not exist here at all. Other conditions come with it too, including that the canner cannot be opened during the process for any reason [F-6.2].

So: same side of 4.6, shorter list. The rest of it, including the two live documents that disagree about this in public, is on steam canning, what changed and when.

Half-gallon jars for a big batch of apple juice?

The guide recognises half-gallon jars for a narrower purpose than most pages report: very acid juices, and nothing else [F-2.8]. That is not a general permission for large jars of fruit, and no tested process exists for most foods in that size.

Read these yourself

USDA Complete Guide to Home Canning, 2015 revision — NCHFP's landing page for the document
nchfp.uga.edu

NCHFP — Recommended canners
nchfp.uga.edu

NCHFP — How do I can tomatoes?
nchfp.uga.edu