A General Guide To Canning Basics


History tends to repeat itself. We’re used to having plenty of everything available in our stores, but as this book goes to press, we’re dealing with less-than-full shelves at the grocery stores, supply chain delivery problems, and a realization that the lessons of the Great Depression have been largely forgotten. Since March 2020, when the COVID-19 pandemic changed our lives, we’ve developed a new appreciation for the thriftiness of our ancestors, and there has been a renewed interest in self-sufficiency and a desire to ensure there will always be enough food for our families.

Many people rediscovered gardening—as a remedy from the enforced isolation and as a means of ensuring their families would have a good supply of healthy food. However, when those thousands of folks began harvesting their crops, the demand for canning jars, rings, and lids caused massive shortages. It’s not just food that we put by; it’s also the supplies that allow us to preserve that food.

When the traditional brands of lids became scarce, some foreign companies were quick to capitalize on the need. Unfortunately, many of these products don’t meet the standards for production set by the US government. Cheaply made products, originating in China, have flooded the market and aren’t safe to use. Other companies in the US have stepped up to the task and produced good-quality items. You can see the difference for yourself in the other photo. The takeaway is to know where your products are made and choose wisely when your health is at stake.

The Science Behind Canning

We have the French to thank for the invention of canning—a candymaker by the name of Nicholas Appert to be precise. When Napoleon Bonaparte offered a prize of 12,000 francs to whoever could develop a system for keeping food fresh for his soldiers, Appert bit. It took him years, but he learned that if he put food in a bottle and kept out as much air as possible through a system of corks, wires, and sealing wax and then heated the foods in hot water, the food didn’t spoil.

Napoleon was impressed with Appert’s canned (or bottled) soups, fruits, vegetables, and gravies and awarded him the prize. The army got to eat unspoiled food and the food canning industry was born. In 1811, Appert published a book explaining his process. Since that time, much has changed, but the basic principles remain: sealing jars to keep out air and then heating the contents of the jars to destroy microorganisms that can cause the food to spoil. Appert didn’t know why the process worked—that discovery was to come later.

Nicholas Appert would be quite impressed with the innovations and equipment now available to the home food preserver. We now know the science behind why his process worked and how to use heat and acidity to create a safe product.

Appert is now considered the father of canning and his birthday, October 23, is National Canned Foods Day. It’s a good day to put up some canned food and honor Nicholas and his contribution to the home arts. (Incidentally, Appert is also the inventor of peppermint schnapps!)

Supplies & Equipment for Canning

Gathering the essential supplies for canning is a bit like organizing a scavenger hunt: some things you already have and some you’ll need to get. If you’re new to home canning, the process might seem rather overwhelming and perhaps a bit frightening. It’s important to relax. Take a deep breath and approach canning with curiosity, enthusiasm, and a touch of respect. It’s called a process because that’s exactly what it is. Just take one step at a time, follow the directions carefully, and you’ll end up with a safe, delicious product.

Boiling Water Canner

Without a doubt, this is the most versatile, handy, wonderful, and indispensable piece of equipment for the home food preserver. You can use it for blanching, making soups, and a host of other tasks—in addition to its primary function as a canner for acidic foods (discussed later in this chapter). In fact, as you get inspired by the possibilities, you might find that one isn’t enough. They’re reasonably priced, beginning at around $25 and going up from there. If you’re heading into a marathon tomato or peach or whatever processing session, it’s wonderful to have two canner loads cooking and reduce your time waiting for one pot to cool down while the jars wait anxiously for their turn.

The boiling water canner (sometimes referred to as a “water bath canner”) is essentially a large pot. It’s made of aluminum or porcelain-coated steel, has a lid with a handle, and comes with a removable rack that holds jars in place while the water boils and also keeps the glass from coming into direct contact with the bottom of the canner. That rack is an essential piece of equipment. Glass jars that come into direct contact with the metal while the heat is on will shatter.

Boiling water canners have either flat or ridged bottoms. If you’re working with an electric range, you’ll want the flat bottom. For gas ranges, the ridged one works well.

These canners come in different sizes, with the standard size able to accommodate 7 quarts or 9 pints with room for the required 1 to 2 inches (2.5 to 5cm) of water needed above the tops of the jars.

Pressure Canner

This is an essential item for canning low-acid foods. It’s probably the most intimidating appliance for a novice, but it’s actually simple to use. Some people fear their pressure canner will explode. The horror story in your family history probably has more to do with Aunt Mabel heading out to the garden and spending the afternoon there (forgetting she had a canner full of green beans on the stove) than any equipment malfunction. If you follow the directions and attend to business, there’s no reason on this Earth for explosions. Pay attention and all will be well.

Pressure canners come in different sizes and are rated by the volume of water they can hold. The standard size pressure canner is a 16-quart model. This means it will hold 16 quarts of water. For canning purposes, it will hold 7 quart jars or 9 pint jars (just like the boiling water canner).

An older–model, dial-gauge pressure canner (left) and a newer-model, weighted-gauge pressure canner (right)

Take some time to become familiar with your canner’s features before you can your first load. Pressure canners have undergone considerable streamlining over the last few decades. They’re more lightweight for sure! Older models were heavy affairs. Models made before the 1970s have thick walls with lids that either clamp or turn on. They have a dial gauge in the lid, along with a vent (either a petcock or counterweight) and a safety fuse. And yes, these veterans are still out there, working away. If you have one of these, it’s important to do a yearly check on your pressure gauge. Your local Extension Service might offer a free checkup for you. You can find your local office with an online search. Newer models have thinner walls and generally have turn-on lids. The lid has a gasket, either a dial or weighted gauge, an automatic vent/cover lock, a vent port that’s closed with a counterweight or weighted gauge, and a safety fuse. Compared with an older model, it has more safety features built in. Here’s how those parts work:

  • Vent port, petcock, or steam vent: These names all refer to the same thing. The vent is the escape hatch for air trapped inside the canner and it also releases steam during processing. It’s part of the pressure-regulating system.
  • Weighted gauge: This is a round piece of solid aluminum with three holes drilled into the side. Each hole corresponds to a different pressure: 5, 10, or 15. If you’re processing foods at 10 pounds of pressure, you put the number 10 hole on top of the vent port. The weight jiggles back and forth during processing, releasing steam and keeping the pressure steady. The major drawback to the weighted gauge is you can’t easily adjust for altitude. (See the discussion later in this section.) If you need to process at 12 pounds of pressure to adjust for altitude, you have no choice but to use the number 15 hole. This can be overkill and you might overprocess your foods. Going below to the number 5 hole isn’t an option because your foods could be underprocessed and potentially unsafe.
  • Dial gauge: More user-friendly than the weighted gauge, you can easily adjust for altitude because the gauge has 1-pound increments. You’ll need to keep a close eye on a canner with a dial gauge and turn the heat up or down as necessary to maintain a constant temperature. Dial gauge canners also have a petcock but no weight to put on it. You have the petcock open (in the straight-up position) during venting and closed (flick it to the side) after venting has been completed and processing has begun. Once the air has been expelled, the petcock is closed or the weight is placed on the vent and processing begins. Dial gauges should be checked for accuracy at the beginning of each canning season and more frequently if you turn it into a workhorse. Contact your extension office for information.
    Safety fuse, safety plug, safety release plug, or overpressure plug: These names all refer to that little rubber plug or thin metal insert that releases pressure from the canner if the pressure gets dangerously high. You’ll notice there’s a red zone on the dial gauge. You want to stay out of the red zone at all costs. Think of it as the RPM gauge on your car. Red is bad. Very, very bad. Fortunately, if you’re paying attention, this shouldn’t ever be a problem.
  • Gasket: This is round and made of rubber or other space-age material and is designed to fit perfectly inside grooves or slots in the lid. Not all canners use gaskets. Check the gasket at the beginning of each canning season to be sure it’s still pliable, hasn’t stretched, and has no cracks. If you detect any damage, purchase a new one. They’re available at many hardware stores and also through the company that made your canner (another good reason to keep the instruction book handy). It’s helpful to keep the instruction booklet in the canner when you’re storing it for the season. That way, you’ll never have to search for it and you’ll be more inclined to refer to it when you should.
  • The rack. Not a medieval torture device, this is a handy part of the canner that keeps the bottom of the glass jars from coming in contact with the hot, hot bottom of the canner. The rack for a pressure canner is constructed differently from one for use in a boiling water canner. It’s a molded piece of aluminum with holes punched in it to allow water to circulate.

What About Other Types of Cookware?

In a pinch, we’ve all used various types of cookware for other than their intended purposes. We’ve boiled water in a pot when the teakettle was out of commission. We’ve made French toast in a skillet if the griddle was otherwise occupied. And that’s just fine. However, when it comes to canning—and pressure canning in particular—substitutions aren’t a good idea and can be downright dangerous.

It’s just human nature to experiment, though, especially when you’ve gotten a new piece of kitchen equipment and you’re working your way through the learning curve. And this is where listening to the experts is definitely a better choice than the self-proclaimed authority at the checkout at the hardware store.

Instant Pots are wonderful additions to the kitchen cookware arsenal. They’re excellent stovetop pressure cookers, shortening the cooking time considerably. However, they’re NOT suitable for canning.

West Virginia’s Extension Service is clear on this: “Although Instant Pots and other electric pressure cookers use pressure to cook, they do not get to the proper temperature and pressure for pressure canning. Consult your user manual for recommendations on hot water bath canning or visit nchfp.uga.edu/publications/nchfp/factsheets/electric_cookers.html for more information.”

Initially, the user’s manual indicated these appliances were indeed safe for pressure canning. This error has since been corrected.

Glass Canning & Freezing Jars

Canning pears with lemon and spices on checkered cloth

You’ve probably heard these jars referred to as “Mason jars.” They’re named for John Mason, who invented a machine back in 1858 that was able to cut threads into zinc lids. After that, it was just one more step to make jars with threads in their necks that would receive the threaded lids for a tight fit. The third piece that completed the seal was a rubber ring that fit between the lid and the jar. Since that time, the technology has vastly improved and simplified the process.

You might not have thought about Mason jars as candidates for holding foods you’ll be freezing, but modern glass canning and freezing jars work just fine. The glass is designed to withstand extremes of temperature and pressure, so they’re truly double-duty items.

The two most commonly available brands of jars are Ball and Kerr, and it’s the same with lids and rings. Prices differ for these two brands, but there seems to be little reason for it. Both are manufactured by the same company, Jarden, which also makes Bernardin and Golden Harvest jars!

You might be wondering about those jars you see at the grocery store that have “Mason” stamped into the glass sides. They frequently contain spaghetti sauce or fruit and you might think they’d be nifty to keep for canning. Unfortunately, these aren’t true Mason jars. The glass is thinner and they’re not recommended for canning and freezing.

Glass canning and freezing jars come in sizes ranging from ½ pint to ½ gallon, with pints and quarts being the ones you’ll use most often. They also come in regular or wide mouth. Regular (or narrow) mouth jars work well for juices, sauces, and smaller-sized items. The wide mouth jars are better equipped to handle bigger fruits, such as pear or peach halves and bulkier vegetables. There’s no difference in the carrying capacity of wide-mouth and regular-mouth jars. If your hands are small and fit inside a regular-mouth jar, you might find you prefer them. If your hands are larger, coping with narrow-mouth jars can get tiresome.

Keep in mind that Mason jars are specially designed and manufactured to withstand temperature and pressure changes. However, if you have any antique canning jars, enjoy them as additions to your home décor, but don’t try to freeze or can in them. Glass canning jars have a life span, as we discuss later on. Bottom line on those pretty blue or rose antique jars: They’re likely to shatter and crack if you don’t respect their venerable age. Fill them with buttons or dried rose petals or whatever else your heart fancies. Just don’t use them for canning or freezing.

Canning Lids & Rings

Jars require lids, which rest on the rim of the jar, and rings, which screw on over the lid. It’s a three-piece set: jar, lid, and ring. Jars and rings are reusable, but lids aren’t unless you’ve purchased reusable lids. The first box of canning jars you buy will also come equipped with rings and lids. If you need additional rings and lids, they’re sold together in a tall box.

Diameter of a Regular-mouth Jar (Left) and a Wide-mouth Jar (Right)

After that, you’ll buy new lids in boxes of 12. You should buy new lids at the start of each canning season, although there’s no guarantee you’re getting a fresh supply. Stores can warehouse them until the following season. If lids are stored in a cool, dry location, the Extension Service notes they can last up to 5 years from the date of manufacture.

Today’s lids are self-sealing, in contrast to the olden days when the home food preserver had to perform several steps to ensure the lids would seal. A modern lid is a round metal piece with a slightly raised dome in the center. You might hear them referred to as “dome lids.” There’s sealing compound around the edge of the lid, which is designed for one-time use only. Used lids can’t be reused and must be discarded.

Also known as “screw bands,” rings last a long time but might eventually rust if they’re in constant contact with moisture. If they rust, toss them and buy new ones. They’ll make a cleaner contact with the threads on the neck of the canning jar, ensuring a good fit, and you can avoid the frustration of trying to force them on if rust is interfering. Rusty rings can prevent your lids from sealing.

Older model canning jars used rubber gaskets and bailing wires attached to the lids. These had to be manipulated after processing, as indicated by instructions that told you to “complete the seal.” Modern reusable lids are a more recent innovation, but they’ve been around for nearly half a century. They’re a bit pricier than their nonreusable cousins, but they can pay for themselves over time. They’re exactly what the name implies. They can be used over and over. They’re used on modern canning jars and there’s no bailing wire system to mess with. However, there’s a thin rubber gasket placed under the lid and secured with a ring.

Always read and follow the manufacturer’s directions. There’s usually an additional step when using reusable lids. From the Extension Service: “Note, manufacturer’s instruction may instruct the user to tighten the metal band immediately upon removal from the canner. If instructed, you should do so. Tightening the screw band ensures that the gasket forms a seal. The metal screw band is removed once the container is cooled and a seal has formed.”

Nifty Gadgets

A jar lifter is essential. Potholders become wet, and when they’re wet, you can quickly get burned. Jar lifters are available at most hardware stores.

A lid wand is a fun gadget. It’s not essential, but it keeps your hands out of hot water when you’re reaching for a lid to place on a jar. It’s a wand with a small magnet at the end that captures the lid.

A canning funnel is a must. It’s wider at the base than a regular funnel and fits nicely into quart or pint jars. It keeps hot foods at a respectful distance from your hands. You’ll find these at hardware stores or other stores that sell canning supplies.

Caring for Your Equipment

At the beginning of the canning season and after each load has been processed, you should carefully clean your canner. Washing the boiling water canner is a simple process. Wash it in regular dish detergent, rinse, and dry. Be especially careful with the wire rack, which loves to rust if given any opportunity to do so. When you’ve finished with the canner for any length of time, be sure it’s completely dry before storing it. Placing a crumpled sheet of newspaper or some paper towels in the bottom of the canner will help draw any moisture away from the rack.

Washing the pressure canner is a bit trickier. If you’ve got a dial gauge lid, you can’t submerge the lid in water. Also, be careful not to invert the lid while there’s still water on it, as that water can work its way into the dial and wreak havoc.

If the vent port ever clogs, thread a needle with heavy-duty thread and draw the thread through the hole. You might find this procedure difficult to explain should a non canning member of your family happen to pass by.

Wash the base in regular dish detergent, rinse, and dry. Avoid using scouring powder or baking soda because they’ll cause the aluminum to turn dark. You can use fine steel wool if you come across some stubborn stuck-on food. Aluminum does have a tendency to pit, so don’t leave food or water in the canner. Also, the canner might absorb odors from food. What this means in simple language is that you shouldn’t use the pressure canner for storing food.

If the petcock is removable, you can wash it as you need to. With either model, be careful not to scrape away at the vent. The rubber material can be damaged if you get too industrious with the cleaning. Discover more about essential and helpful canning and preserving equipments.

Using Your Canners

Boiling water canners and pressure canners have different procedures for use.

Boiling Water Canner

Fill the canner one-half to two-thirds full of water. Raise the jar rack and secure it on the rim of the canner by hooking the handle slots on the rim. Turn the heat on high and set the lid in place. When the water has come to a boil, use a jar lifter to place jars in the rack slots. Then lift the rack handles and reposition the rack inside the canner. Replace the lid. When the water returns to a boil, begin timing. When the processing time has been completed, turn off the heat, remove the lid (being careful to turn it away from you to avoid a steam burn), and use the jar lifter to remove jars from the canner. Place them on a clean, dry dish towel. Don’t touch them again until they’ve sealed. You might hear a distinctive “ping” as the seal sets. Leave the jars undisturbed overnight.

Pressure Canner

Place the rack in the canner. It will sit on the bottom. Put 2 to 3 inches (5 to 7.5cm) of hot water in the canner. The water will come through the holes in the rack and fill the bottom of the canner. Turn the heat on high. When the water begins to boil, use a jar lifter to position the jars on the rack inside the canner. One jar will go in the center of the rack. The rest will form a circle around the center jar. Try to keep them from touching each other. Secure the lid. Leave the petcock in the open position. When steam begins escaping through the vent in a steady stream, set the timer for 10 minutes. After the canner has vented for 10 minutes, close the petcock or place the weighted gauge on the vent.

The pressure will now begin to build inside the canner. If you’re using a weighted gauge, the gauge will begin to rock and jiggle when the correct pressure has been reached. Check your owner’s manual to find out how often the gauge should jiggle. You can control the frequency by controlling the heat on the stove. For example, if the weight is jiggling too often, reduce the heat. If it’s not jiggling often enough, increase the heat. Once you’ve found the correct heat and the gauge is operating correctly, begin to time the processing.

If you’re using a dial gauge, you’ll see the pressure begin to climb. When the pressure has reached the correct level, turn down the heat as necessary to maintain that temperature. With an electric range, begin reducing the heat just before the needle indicator reaches the correct level. Gas ranges respond more quickly. Then begin to time the processing. It might take a little finessing to arrive at a steady pressure, but be patient. You control the heat. You control the pressure. You are in control!

When the processing time is up, turn off the heat and do nothing else! The canner will gradually lose pressure and you should do nothing to try to speed up the process. There are several good reasons for this:

  • You could warp the canner.
  • You could cause the jars to break.
  • You could prevent the jars from sealing.
  • You could draw liquid from the jars.
  • You could get a really nasty burn.
  • Newer-model canners have vent locks that relax and return to the normal position when the pressure reaches zero. When the pressure has reached zero, it’s time to remove the weighted gauge if your canner has one and wait 2 minutes more. Then open the lid and remove the jars. Always turn the lid away from you to prevent a steam burn. The contents will still be boiling hot even though the pressure part of the processing has been completed.

Use a jar lifter and place the jars on a flat, dry surface. A folded, dry kitchen towel works well. Allow the jars to cool and form their seal. Again, this is a process you mustn’t rush. Once you’ve negotiated your first load of canning, celebrate! You’ve made the grade!

Getting the Best Products

Each load you process represents hard work and a financial investment. In addition to obtaining and caring for your equipment, there are some things to learn about the process to make sure your results come out top notch. Two of these must-know topics are acidity and heat.

Understanding Acidity

Preserved lemons and almonds in glass jars on table

Acidity is the most important factor in determining how foods should be processed. Foods are divided into acid and low acid for purposes of canning. Their level of acidity is determined by the pH scale, which ranges from 0 to 14, with 7 being neutral. For foods to be considered acid, they must have a pH of 4.6 or lower.

Acid foods contain enough natural acidity to prevent the growth of heat-resistant bacteria or they’re able to destroy them more rapidly during processing. Foods that can be safely canned using the boiling water bath are acid, have acid added to them (citric acid, lemon juice, or vinegar), or are fermented.

Over the years, new varieties of foods have been introduced and older varieties have been hybridized. In some cases, this has resulted in a change in their acidity. Tomatoes are a case in point. No longer as acidic as they used to be, it’s necessary to add lemon juice to the jar before processing to ensure a safe product. Exact amounts are indicated in individual recipes.

Low-acid foods (those with a pH above 4.6) must be processed in a pressure canner to ensure a safe product. They don’t have the natural acidity to prevent heat-resistant bacteria from growing. They need help. They need a heat boost—and that’s delivered with pressure.

What You Need to Know About Bacteria

Bacteria are microscopic organisms that are present everywhere—in the air, in the soil, even on your skin. Some are beneficial (such as the bacteria in milk that help produce yogurt), but many are harmful, including those that cause botulism.

The common bacterium Clostridium botulinum is found in soil everywhere in the world. Soil in the western US is particularly high in the type of this bacterium (type A) that’s especially dangerous to people.

You’ve no doubt read about cases of botulism, but just how rare are these occurrences? The answer is fairly rare because certain factors have to be in place for people to become sick. The bacterium has to be present in the food, the food has to be low in acid, and the food has to have been improperly processed.

The home food preserver can take measures to prevent this bacterium from contaminating home-preserved foods. The procedure is simple: Always pressure-can low-acid foods and follow research-based, approved recipes. For added safety, boil low-acid home-canned foods for 10 minutes at sea level before serving. The botulinum toxin is destroyed by boiling. This is why previous generations of home food preservers boiled the heck out of their vegetables before putting them out on the table for dinner. However, you don’t have to cook your vegetables until they’re mush for them to be safe. Just do the job right and don’t take shortcuts. Read up on the brief history of preserving foods.

Turning Up the Heat

Water boils at 212°F (100°C) at sea level. As the altitude increases, atmospheric pressure drops and the temperature at which water boils also drops. This means that no matter how long you boil the water, its temperature won’t increase.

In the case of low-acid foods, this is a problem. Clostridium botulinum spores aren’t killed at the normal temperature of boiling water. In order to kill them and prevent botulism, you must raise the temperature of the food being processed from 240°F to 250°F (115°C to 120°C). This is accomplished with pressure. As you increase the pressure, the temperature rises. Enter the pressure canner—your number one food safety insurance policy. The length of processing time depends on a variety of factors: the level of acidity of the food, the size of the jars, and how tightly you’ve packed those jars, for starters. That’s why you’ll find specific times and pressures for each food in the directions for processing that food.

Altitude Adjustments

You read in the last section that water boils at 212°F (100°C) at sea level. If you live at 4,000 feet (1.2km), water boils at 204°F (95°C), and if you’re on top of the mountain at 8,000 feet (2.4km), it’s a mere 197°F (92°C). To make sure your food is safe, you’ll need to adjust your pressure reading to reflect your own altitude. For example, if you live at 5,000 feet (1.5km), you’ll need to up the pressure from 10 to 12½ pounds (4.5 to 5.7kg). This is much more easily done if you’ve got a pressure canner with a dial gauge.

You’ll need to determine your elevation above sea level. There are a few ways to go about this, but the easiest is probably to simply do an online search. One option is to go to www.whatismyelevation.com. Another is to use the US Geologic Service’s National Map: apps.nationalmap.gov/elevation.

Consult your canner instruction book for the chart that tells you what pressure you’ll need to use. The general rule is to add 1 pound of pressure for each 1,000 feet (304m) above sea level. Processing times remain the same regardless of your altitude.

Hot Pack vs. Raw Pack

These terms refer to the temperature of the foods you’re putting in the jars. In hot pack, you’ll heat the food in boiling water, syrup, or juice before you pack it into jars. In raw pack, you pack the food into jars without heating it and then add liquid to cover. Both hot pack and raw pack have advantages:

The advantages of hot pack:

  • The food is softer and easier to fit into jars.
  • More food can fit in the jar. Foods might contain up to 30% air. Cooking releases this air.
  • There’s less of a problem with floating food.
  • Color and flavor might be better than raw pack after time in storage.
  • It increases the vacuum in sealed jars.

The advantages of raw pack:

  • It’s better for foods that tend to lose their shape after cooking.
  • It’s perhaps less time-consuming than hot pack depending on the food.
  • Measuring Correct Headspace

The headspace is the area in a canning jar between the top of the food and the bottom of the lid. Because many foods expand during processing, it’s important to leave the correct headspace for the food you’re canning. Each recipe will tell you how much headspace to leave. If you don’t leave enough headspace, your food is likely to erupt through your carefully prepared lid and ring, turning your canning liquid into a murky mess. Your jars will also not seal properly, so don’t try to squeeze that last tablespoon of whatever into the jar when you know in your heart it’s going to play havoc with your headspace (including your own).


Most of the time, everything turns out fine. Sometimes, though, in spite of your best efforts, weird things happen. There’s always a logical reason why. Here are some of the most common problems, along with their causes and solutions.

Why Jars Break

In addition to using jars not suited for canning (such as mayonnaise jars or those grocery store jars we talked about earlier), having the bad luck to have a jar with an imperfection, or using old jars, there are three basic causes of breakage: thermal shock, pressure, and impact. Canning jars are tough, but they do have their limits. Nothing lasts forever. Canning jars have a limited life expectancy. After about 12 years, it’s time to take them to the recycling bin.

Thermal shock, as the name implies, has to do with temperature extremes. The jar generally breaks into a few large sections. You might encounter this if you forget to put the rack in the bottom of the canner, if you decide to cool the jars by running cold water over them, or if you take a cold jar and dump it into boiling water.

Solution: Avoid subjecting jars to temperature extremes and do a checklist of procedures before you commit the canner to the stove. This includes checking to be sure you’ve put the rack in the bottom of the canner!

Pressure breaks occur when the pressure takes some wild swings during processing because you’ve forgotten to keep an eye on the dial gauge. This can also happen if you give in to temptation and try to hasten the depressurizing process by nudging the petcock. If you screw the jar lids on so tightly that nothing can escape—not even the air that needs to—or pack the jar to the tippy top and forget about headspace, you can also have a pressure break. These breaks can result in spidery lines, along with big cracks.

Solution: Follow procedures to the letter. Don’t try to rush the process at any point and always attend to what you’re doing. This means staying in the kitchen while you’re processing foods with the pressure canner.

Impact breaks happen if you drop, bang, or subject the jar to some sort of insult. Using a sharp knife to remove air bubbles can also cause these kinds of breaks if the knife tip jabs into the side of the jar. These breaks have a central hole with radiating cracks.

Solution: Use a rubber spatula to remove air bubbles. And, of course, try not to drop the jars. Always inspect jars carefully for nicks, scratches, or cracks before using them. Recycle the ones that fail the test. And never, never, never bang the jar on the counter to settle the food before you consign it to the canner.

Failure to Seal

Why didn’t my jar seal? This is the most plaintive cry of the home food preserver. After everything you did for it, it repays you by doing absolutely nothing. It just sits there.

Usually, after you’ve given it more than enough time to do the right thing, you’ll unscrew the band and remove the lid to find a bit of food stuck to the adhesive compound. That’s the most common culprit.

Here are some other possibilities:

  • Using old lids for which the adhesive compound has degraded
  • Not leaving the correct headspace
  • Not following correct processing times or procedures
  • One other possibility is you tried to save a bit of time and used the open kettle method instead of opting for the good old boiling water bath. The open kettle method was an older way of putting up fruits, such as peaches. The peaches were heated in juice or water to boiling and then packed boiling hot into glass canning jars. Lids were adjusted and then left to seal on their own. Sometimes they did and sometimes they didn’t. Sometimes they unsealed during storage. It’s not the recommended way to ensure a good seal and can result in a whole lot of spoiled food. I know, you were told your great-great-grandmother did it this way and it was always fine. But it wasn’t always, and besides, she used a button hook to fasten her shoes and wore a corset. We don’t use those any longer either. So … what to do? You can either reprocess the food right then and there or put it in the refrigerator to use within a few days.

Explaining Liquid Loss

This often occurs when the pressure fluctuates during processing or if someone has opened the petcock prematurely. The jar of peaches on the right has the correct amount of liquid. The peaches are nestled nicely in syrup. The jar on the left has lost so much liquid that the peaches are almost certain to turn brown. Which jar would you be proud to claim as your own?

In a boiling water bath, the water must be 1 to 2 inches (2.5 to 5cm) above the tops of the jars or water will be sucked out of them during processing. In a pressure canner, you can get liquid loss by not letting the pressure canner exhaust for 10 minutes before beginning processing. What this means is that there’s still air inside and you’ve not completely pressurized your canner. That air sucks out the liquid.

Other possibilities include the following:

  • Not taking the jars out of the canner when processing has stopped but allowing them to cool down in the canner. This most often happens when you’ve decided to do one last load before bedtime and figure you’ll just take out the jars in the morning. The solution here is to plan your day and keep to the plan.
  • Not removing all the air bubbles from the jar before processing. You’d think that just pouring the liquid into the jar would fill in all the spaces between the pieces of food, but it isn’t so. Air gets trapped in the smallest depressions—for example, in the hollow of peaches where you’ve removed the pit. When you place the peach pitted side down in the jar, you’ve left an air pocket. The solution here is to gently use a rubber spatula to lift the fruit to allow the liquid to fill the space. You can’t see into the middle of the jar and it’s likely there are also small air pockets there. Run the spatula around the edges of the jar. This will move the food that’s in the center of the jar and allow the liquid to penetrate thoroughly.
  • Packing the jars too tightly or too full. This often happens when you’re down to your last jar to make a full canner load and you’ve got more food than the jar should take. You’re trying to use every bit of food, so you cram it all in; however, food expands during processing and this drives out the liquid in the jar. As the jar cools down, that liquid loss becomes depressingly apparent. Always leave the necessary headspace. You have options for that extra food. You can eat it, of course, or you can refrigerate it overnight and add it to the next day’s processing load.
  • Starchy foods in the jar absorbed the liquid. Corn is a real culprit here. As the processing time bubbles along, the corn cooks and plumps beautifully. However, this plumping happens because the corn has availed itself of the liquid you so thoughtfully provided. Follow the directions carefully for the correct headspace for starchy vegetables.
  • Liquid loss from too little headspace (left) and a good amount of liquid (right)

When faced with liquid loss, what do you do? If the jar has sealed, the food is safe to eat, although you should eat it as soon as possible. The top layer is likely to darken, but you can remove this before using the rest of the contents.

When to Reprocess

The decision is up to you. If the additional processing time (and you’ve got to redo the whole time) won’t turn the food to mush, go ahead and reprocess it. Decide then and there. You’ve only got about 24 hours with the food kept under refrigeration to make up your mind before the spoilage microorganisms wake up and get to work. If you don’t want to spend the time or energy, just make plans to eat the food.

Food that’s been sealed, stored, and then unsealed shouldn’t be reprocessed. Toss it. Common sense should be your best indicator when it comes to determining whether you’ve got a problem or an irritation.

If you detect mold or a strange odor or if the liquid has turned cloudy in the jar, discard the food. If your food is bubbling, this is definitely not a good sign. Your food shouldn’t be moving under any circumstances. Don’t taste it. Destroy it.

Safe Disposal

The Centers for Disease Control (CDC) has guidelines for the proper ways of disposing foods that are suspected of harboring the botulinum toxin. It recommends extreme care because even a small amount of the toxin is dangerous and can be absorbed through a break in the skin or through the eyes. Their recommendations are found on their website (www.cdc.gov/botulism/botulism_faq.htm) and are as follows:

  • Place any food you think is contaminated in a sealable bag, wrap another plastic bag around the sealable bag, and tape it tightly. Place the bags outside in a trash receptacle for nonrecyclable trash. Make sure they’re out of reach of people and pets.
  • Never discard the food down a sink, garbage disposal, or toilet.
  • Avoid contact with the skin. Wear rubber or latex gloves when handling open containers of food you think might be contaminated. Wash your hands with soap and running water for at least 2 minutes after handling food or containers that might be contaminated.
  • Clean up any spills using a bleach solution (use ¼ cup of bleach for every 2 cups of water). Completely cover the spill with the bleach solution, then place a thick layer of paper towels on top of the bleach solution. Let the towels sit for at least 15 minutes, then dispose of them in the trash. Wipe up any remaining liquid with new paper towels. Clean the area with liquid soap and water to remove the bleach. Wash your hands with soap and running water for at least 2 minutes.
  • Discard any sponges, cloths, rags, gloves, and containers that might have come into contact with contaminated food.
  • Putting Canning to Work for You

Putting up food by canning is fun, thrifty, and healthful when you do it right. If you start with the freshest ingredients and follow strict guidelines for cleanliness and approved procedures for processing, you’ll fill your pantry with fruits, vegetables, meats, and all manner of tasty products to last you the year.

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