Pressure Canning Basics

Introduction

Have you ever wondered why pressure canning works? It’s actually a simple concept, and, if you are a bit of a science geek like me, quite fascinating!

The goal of pressure canning is to expose food to a high temperature under a specific pressure for a specific period of time to destroy microorganisms that are harmful if eaten. Pressure canning allows food to be heated to 240°F (116°C)—the temperature necessary to destroy these microorganisms, including the botulism bacteria.

Botulism is rightfully one of the biggest fears for those new to canning or those who don’t can. It is flavorless and odorless. Even worse, it cannot be destroyed by boiling or hot water bath canning, which only reaches 212°F (100°C) regardless of how long you boil the food. Botulism thrives in low-acid foods, in moist environments, and in an anaerobic (no oxygen) environment. All these conditions are present inside an improperly processed jar of food. Luckily, proper pressure canning creates a higher-temperature environment and can eliminate the risk of botulism in hours.

The other big fear when it comes to pressure canning is the safety of the pressure canner itself. Through the rest of this section, we’ll discuss pressure canners, essential equipment, and using the pressure canner for the first time. By the end of this section, your fear should be a thing of the past, replaced by excitement to try your first recipe!

Pressure Canning Equipment

When I started canning, I was a purist. I wanted to pretend my grandmother was a homesteader and she was teaching me her ways in the kitchen. I wanted to use only equipment she would have used—and everything needed to have a history. Soon, though, the reality was I needed to can large quantities to feed my growing family. There just weren’t enough hours in the day to hand-shred 50 pounds (22.7 kg) of zucchini!

As I started using my food processor, a professional-quality chef’s knife, and recipes with precise measurements and clear instructions, my canning became more efficient—and productive. I still have some of my old-fashioned equipment, but it has found a new home—lovingly displayed on the top of my cupboards!

That said, the equipment needed for canning is not extensive and it is affordable. If you’re an avid home cook, you may already own much of what you need except, perhaps, the canner itself. See Canning Equipment. Other than the canner, jars, and lids, most items are recommended for your convenience. Let’s discuss about fermented foods.

The Pressure Canner

Stainless steel pressure canner used for home canning

A pressure canner is, essentially, a heavy kettle designed to withstand higher pressure than a normal pot. While models vary in their features, all pressure canners offer a few common elements.

Before we get into the nuts and bolts (for some models, I mean that literally!), know this:

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as mentioned previously, a pressure cooker is not the same as a pressure canner. Yes, both devices use pressure and they look similar. However, pressure cookers are not designed for canning. Most models aren’t large enough for cans and they don’t have pressure gauges.

Pressure canners come in a wide range of models and sizes. When choosing the right model for you, consider how much you’ll be canning at one time; for most people, a pressure canner in the 16- to 22-quart (15 to 21 L) range will do the trick. The other main differences will be the gauge type (dial versus weighted) and cover type (metal-to-metal or lock-on with gasket). Let’s get to it.

Locking cover:

Strawberries in a jar being prepared for preservation

All pressure canners have a locking cover that can be closed in only one correct position. There are canners with covers that lock on with a rubber gasket between the cover and kettle, and other canners that have individual locking wing nuts around the edge. I have both styles and still use them both every year. Neither one is better, objectively, but I find I reach for the model with the gasket and lock-on cover more often.

I do this because the locking process for the pots is different and I prefer the locking procedure on the cover with the gasket. Unlike a metal-to-metal cover, which requires manual tightening, lock-on covers with gaskets have a specific closing procedure with matching markings for the lid and pot and/or clamps. This means there’s either a “locked” or “not locked” situation and no guessing as to the tightness of wing nuts. (Is this tight enough? Did I overtighten?)

NOTE

Weighted gauge models do not self-correct for altitude adjustments. This means at altitudes above sea level (higher than 1,000 feet [304.8 m]), the pressure you set should be adjusted upward.

No matter which lid type you have, always follow the manufacturer’s instructions for locking the lid. Also, note that if your lid has a gasket, you’ll need to clean it according to your manufacturer’s instructions and use care. For example, some models may tell you to lubricate gaskets with cooking oil while others do not. Any damage to a gasket can affect the machine’s ability to hold pressure correctly. Regularly inspect your gasket and replace at the first sign of wear.

Pressure gauge:

Another feature that all pressure canners share is a gauge that displays the pressure inside the canner. There are two types of gauges and both work equally well. The first type of gauge is a weighted gauge. This gauge has no dial face, but instead has numbers engraved around its edges. This gauge will rattle when the correct pressure is reached; then, it will rattle faster and allow some steam to escape if the pressure gets higher than necessary. Note that it’s not better to have slow or fast jiggling with this type of pressure gauge. The fact that it is moving means it is maintaining the recommended pressure. In my opinion, this gauge is more foolproof as it requires less heat adjustment than a dial gauge.

The second type, a dial gauge, is an easy-to-read, clock face–style gauge. It has a hand that moves as the pressure increases. You adjust the heat while you watch the gauge. Start the timer once the canner gauge reaches the correct pressure and adjust the heat level with the goal of keeping the pressure gauge at the correct number for the period of time specified in the recipe.

As mentioned elsewhere, it’s important to check your gauge for accuracy at least annually. The start of a new canning season is a great time to do this. Your county’s cooperative extension office should be able to help and some manufacturers offer this service as well. Learn about lacto-fermentation.

Release valve and overpressure plug:

On the cover of your pressure canner, there is a release valve, which can also be referred to as a vent tube, petcock, or pipe vent in the manufacturer’s manual. This release valve needs to be checked at the start of each canning session. Simply hold the cover up and make sure you can see light through the vent tube. If not, clean it with a pipe cleaner or however the manufacturer recommends. Note that this valve is where steam will come out and there are models where the weighted gauge will be on the valve.

Your pressure canner will also have an overpressure plug or safety fuse. This is a simple release that functions as a backup to the primary release valve/vent tube. The overpressure plug opens if the pressure gets too high due to the release valve being blocked. It is a safety feature not present on old-style pressure canners, and you should not use a pot that’s so old it does not have this important feature. This backup release mechanism is there for your safety. You should also look for the Underwriter’s Laboratory (UL) seal to ensure the device’s safety.

The manufacturer of your pot may have recommendations for keeping the release valve and overpressure plug clean and operational. Always follow the best practice directions for your pot.

Canning rack:

Finally, your pressure canner will come with a rack. The rack will look like a circular dish with holes in it and it’s designed to sit on the bottom of the canner. Jars will sit on top of the rack; its design allows for the circulation of steam around the jars. It also helps stabilize your jars so they don’t knock together or against the sides of the canner (possibly breaking them). If your canner did not come with a rack or your rack breaks, you need to buy a new one. The best place to start is the canner’s manufacturer. Don’t can without a rack.

Let’s Talk about Jars

Jars are about to become your new best friend. There are as many styles, sizes, shapes, colors, and uses for these sturdy glass containers as there are foods to put in them. Yet despite the fact that most jars have the same purpose (food preservation), not all jars are created equal.

The canning jars I recommend are the modern-style canning jars made by Ball and similar manufacturers. They are distinguished by their sturdy glass, clearly marked volumes, and 2-piece lids.

The main alternative to this style of jar is experiencing a resurgence, though more as a dry storage jar than for canning. This alternate style of jar, called a bail-type jar, made famous by Weck, has two glass pieces—the jar and the lid—that are sealed together using a rubber gasket. Metal clips or a wire were used in conjunction to hold the lid on while canning, but the rubber seal acts like the modern seal under the lid to create the airtight environment you need to can.

While this type of jar may be used for canning, I tend to recommend it for refrigerated or dry storage instead. Weck jars with brand-new rubber seals may be used if you follow the manufacturer’s instructions, but they tend to fail the beginning canner more often. Even worse, similar-looking vintage jars may not be intended for pressure canning at all. If you collect glass jars to reuse for food storage like I do, keep them in rotation only for dry goods.

So, what other options do you have within the recommended type of jars? You have a variety of sizes to choose from. Most of the recipes in this book all come with a recommended jar size. Other considerations include the size of your canner, which may not accommodate the largest jars.

The other important consideration is the size of the jar’s mouth opening. Canning jars commonly come with two options:

  1. Regular-mouth jars have a small opening, about 2⅜ inches (6 cm), but are good for liquids such as stocks or juices, and brothy soups. While many canners use only regular-mouth jars and have no trouble, keep in mind that regular-mouth jars are a little harder to clean if there is residue inside.
  2. Wide-mouth jars are my personal favorite for a few reasons. You can easily get a utensil inside to scrape them clean. I also like wide-mouth jars because, with their opening at about 3 inches (7.5 cm), the jars are easier to fill for recipes with larger pieces. If your recipe will retain a firm texture, it’s easier to remove the vegetables when serving as well.

There are many canning jar sizes, from half pints (235 ml) all the way up to gallons (liters), although these large jars are not usually used by home canners. With even grocery stores selling canning jars these days, you can easily find the right jar for the job. Most of the recipes in this book, and elsewhere, recommend a specific size. For safety reasons, use the recommended size and don’t switch up sizes unless there is a corresponding recommendation for canning. Let’s look at some of the jars you’ll use!

Jelly jar:

Not just for jellies and jams, these jars come in a range of sizes from 4 ounces (120 ml) to 12 ounces (355 ml). They are the perfect size for gifting and for the little condiments you want on the table, without having to eat from the container for an extended period of time. Can you imagine a quart (946 ml) of mustard, for example? Use jelly jars for mustards, ketchups, barbecue sauce, and small-batch recipes.

Jelly jars can also highlight a particular food. Jelly jars have wide openings so you can get out every last bite, and they are easy to clean. Due to their size, they require less processing time, which can be an advantage come canning day.

Half pint:

The half-pint jar gets quite a bit of mileage in my kitchen. When it comes to volume, these jars hold 8 ounces (235 ml) of food—and they also have the benefit of a wide mouth. I think it’s the perfect size jar for relishes, pickles, and chunky chutneys. I use them exclusively for foods I want to use up quickly.
Pint: Pint jars hold 16 ounces (473 ml) and can be used for many items. I use pints for soups I want to package as single lunches, salsas, and specialty recipes like cocktail onions. Pints are a manageable size for most recipes unless you are canning for a large family.

Quart:

Speaking of canning for the whole family, quart jars are my biggest workhorse. Quarts hold 2 pints (946 ml), so you can package double the soup, sauce, etc. I always use quarts to can tomatoes, family-size recipes of sides like baked beans, and soups and broths meant to serve more at once. If you are canning sweet fruits, you may want to consider quart jars. It all depends on how fast your family goes through the food—in my house, the sweets go fast!

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