Pressure canning soup, and a chili to start with

Every autumn somebody asks me whether they can put up soup the way their grandmother put up tomatoes — a boiling-water bath, the big enamel pot, the jars clinking. The answer is no, and the reason is worth understanding rather than memorising, because the reason is what keeps you from cutting a corner later. Tomatoes are acid. Soup is not. A sealed jar of low-acid food, warm, airless and wet, is the environment Clostridium botulinum evolved for: its spores survive boiling water indefinitely, wake up in the jar, and make a toxin you cannot see, smell or taste. Killing the spore takes 240 °F, and water at sea level will not go past 212 however long you boil it. The only way to reach 240 in a kitchen is under pressure. So soup is pressure-canned, or it is frozen, or it is eaten this week. Those are the choices.

This is the post I would have wanted the first time: what the canner is and is not, the few tools that matter, the run from lid-on to lid-off with the places people go wrong, where the tested recipes live, and the recipe to start on. The recipe is chili con carne, and it is the one to learn on precisely because it is the one you cannot improvise — the proportions and the process are the USDA's, and the point of the first batch is to do exactly what the book says and find out what that feels like.

The tools

A pressure canner. Not a pressure cooker, and not an electric multicooker with a "canning" button — the USDA guide is explicit that the tested processes assume a canner large enough to hold at least four quart jars standing upright, and the heat-up and cool-down of a small or electric pot are part of the process time and were never measured. There are two kinds of gauge. A weighted gauge is a metal weight that sits on the vent and rocks or jiggles at its set pressure; it cannot drift, it needs no testing, and it is set in steps of five pounds. A dial gauge shows the pressure continuously and can be read to the pound, and it can be wrong: a dial should be tested every year, which many county Extension offices will do for nothing. Either works. The pressures in the table below differ between them because the weight's steps are coarse and the dial can be set finer.

Jars and lids. Mason jars made for canning — pints, for chili; the USDA has no tested process for chili in quarts, because the jar is too dense for the heat to reach the centre in a time anyone measured. Check every rim for a chip by running a finger round it; a chipped rim will not seal. Two-piece lids: a flat lid with a sealing compound, used once and thrown away, and a screw band, used forever. New flat lids every time, no exceptions.

The small things, each of which exists for a reason you discover by not having it: a jar lifter, because a pint of chili at 240 °F does not come out of a canner with a dish towel; a wide-mouth funnel, so the rim stays clean; a thin plastic bubble tool with headspace notches on it (a chopstick does, a metal knife does not — it can scratch the glass and start a crack); a magnetic lid wand, which is a convenience; a timer you trust; a thick towel for the counter; and a permanent marker, because every jar gets its contents and date on the lid. That is the whole kit. The canner is the expense, and it lasts decades.

The run

Before anything. Know your elevation, because the pressure depends on it: at higher altitude water boils cooler, so the canner has to run harder to reach 240 inside the jar. Most of the Bluegrass sits under a thousand feet — Lexington is about 980 — and east of Berea the ground climbs past it; look yours up once. Then put the rack in the canner and two to three inches of water, or whatever the manufacturer says, and start it heating with the jars standing in it so they are hot when you fill them. A hot jar into a hot canner; a cold jar into a hot canner is how you learn what thermal shock sounds like.

Filling. Ladle through the funnel, leaving one inch of headspace — the gap between the food and the rim, which the processing time assumes, because the contents expand under pressure and the air in that gap is what gets driven out to make the vacuum. Run the bubble tool round the inside of the jar; bubbles trapped in a dense soup lower the level once they escape, so re-measure the headspace and top up. Wipe the rim with a clean damp cloth — a smear of chili between the rim and the lid is the most common reason a jar fails to seal. Lid on, band on fingertip tight: snug, not cranked. Air has to get out past the lid during processing; a band screwed down hard traps it, and the lid buckles.

Venting. Lock the lid, heat high, and let steam pour from the vent in a steady column for ten minutes by the clock before the weight goes on or the petcock closes. This is the step people skip because the canner is obviously hot and obviously steaming, and it is the step that matters most: air trapped in the canner means the temperature inside is lower than the gauge claims. A canner at ten pounds that was not vented is not at 240 °F. Ten minutes, then the weight.

Processing. The clock starts when the canner reaches pressure — ten pounds on a weighted gauge, eleven on a dial, at this elevation — not when the burner goes on. Hold it there for the full time, which for chili in pints is seventy-five minutes. Watch it. If the pressure ever drops below the target, for any reason, bring it back up and start the seventy-five minutes over from zero; the process time is a single uninterrupted hold, and a dip in the middle is a dip the spore noticed.

Coming down. Heat off, and then nothing. The canner comes down to zero on its own, which takes a while, and the waiting is part of the process: the jars are still cooking as it cools, and the time was measured with that cooling in it. Never run water over the canner, never lift the weight to hurry it, never crack the lid. When the gauge reads zero and the weight lifts without a hiss, take the weight off, wait ten more minutes, then open the lid away from your face. Lift the jars straight up and out onto the towel, an inch apart, and leave them alone for twelve to twenty-four hours. Do not tighten the bands, do not press the lids, do not tip them. The pings as the lids pull down are the only sound in the kitchen worth listening for.

Afterwards. Press the centre of each lid: a sealed lid is concave and does not move. Any jar that did not seal goes in the refrigerator and gets eaten this week, or is reprocessed with a new lid inside twenty-four hours. Take the bands off the sealed jars — a band left on can hold a failed seal shut and hide it, and it rusts — wipe the jars, label the lids, and store them cool and dark. Best within a year; safe longer if the seal holds. And the rule that overrides every other: a lid that is bulging or loose, a jar that spurts when opened, an off smell, cloudiness that was not there — do not taste it to check. Not a spoonful. Dispose of it where nothing can get at it.

Those are the USDA's figures and they are the whole table. A soup with seafood in it is a hundred minutes either size. The general soup process — cook the solids, cover with broth, boil five minutes, fill the jars half with solids and top with liquid, one-inch headspace — covers vegetable, bean, meat and poultry soups alike, with two rules that catch people: dried beans or peas must be fully rehydrated and cooked before they go in, and nothing is thickened. No flour, no cornstarch, no roux, no pasta, no rice, no dairy. A thick soup heats from the outside in too slowly for the time to reach its centre, and none of the tested times were measured on a thickened one. Thicken in the pot when you open the jar.

Chili con carne

This is the USDA's recipe, from the Complete Guide to Home Canning, reproduced as published, and the restraint is the point. Nine pints.

• 3 cups dried pinto or red kidney beans
• 5½ cups water
• 5 teaspoons salt, in two parts
• 3 pounds ground beef
• 1½ cups chopped onions
• 1 cup chopped peppers of your choice (optional)
• 1 teaspoon black pepper
• 3 to 6 tablespoons chili powder
• 2 quarts crushed or whole tomatoes

Wash the beans and put them in a two-quart saucepan with cold water to two or three inches above them; soak twelve to eighteen hours. Drain and discard the water. Combine the beans with the 5½ cups of fresh water and two teaspoons of the salt, bring to a boil, reduce the heat and simmer thirty minutes. Drain and discard that water too. Brown the beef with the onions and the peppers, if using, in a skillet, and drain off the fat. Add the remaining three teaspoons of salt, the black pepper, the chili powder, the tomatoes and the drained beans. Simmer five minutes. Do not thicken. Fill hot pint jars, leaving one inch of headspace, remove the bubbles, wipe the rims, lids and bands, and process as above: seventy-five minutes at pressure.

What you may change: the kind of pepper, the amount of chili powder within its range, the cumin and oregano you will inevitably add to the dry spice, the salt. What you may not: the proportions of beans, meat and tomato, the jar size, the headspace, the time, and the thickening. The recipe is thin on purpose and it tastes thin out of the jar on purpose; it is a base. Open a pint, put it in a pot, reduce it, add the masa or the cornmeal or the square of dark chocolate, and it becomes your chili in ten minutes. That is the deal with canned soup generally: the jar holds the hour of work, and the last ten minutes happen fresh.

Where the real information is

Everything above is the USDA's, and you should read it from them rather than from me. The National Center for Home Food Preservation at the University of Georgia (nchfp.uga.edu) publishes the USDA Complete Guide to Home Canning in full and free, and its Guide 5 is the pressure-canning section: every tested soup, meat, vegetable and chili process, with the altitude tables, and the recipe above verbatim. Your canner's manual is the authority on the canner itself — how much water, how its gauge reads, how it locks — and manufacturers differ. The Ball Blue Book is the kitchen-counter version of the same science, tested recipes only. And your county Cooperative Extension office — in Kentucky, the University of Kentucky's — is where a dial gauge gets tested, where the canning classes run every summer, and where somebody will answer the question you are embarrassed to ask. The one source to distrust is any recipe, however beloved, that has not been through one of those. A recipe from a website, a church cookbook or a relative is a recipe for the pot; for the jar, the tested recipe is the law, and the reason it is the law is in the first paragraph.

None of this is difficult. It is a sequence, with three places where the sequence is load-bearing — the ten minutes of venting, the uninterrupted hold at pressure, and the slow cool-down — and a list of things not to change. Do those, and the shelf in the basement will carry you from the first frost to the first asparagus.