Canning is a method used to preserve fresh food in jars using high temperatures to kill microorganisms and inactivate enzymes that could cause food to spoil. The heating process pushes air from the jars, creating a vacuum seal as jars cool. Without air, the bacteria, yeast and mold will not grow and food won’t spoil.
The Two Canning Methods: Water-Bath and Pressure Canning
To can your produce properly and safely, follow one of these methods: water-bath canning or pressure canning.
Which method to use? This depends on the acidity of the food you are canning. A pH higher than 4.6 means less acidity (“low-acid foods”) and a pH lower than 4.6 means more acidity (“high-acid foods”).
The important thing to know is: Low-acid foods must be processed using pressure canning, while high-acid foods may be processed using either water-bath canning or pressure canning.
1. Water-Bath Canning
Water-bath canning is the simpler of the two canning methods, as it involves boiling your food in glass jars in a big pot of water. There are pots specifically designed for this—called water-bath canners or boiling water canners—that consist of a large pot, a rack insert and a lid. However, a large, deep pot will do, as long as you have a rack that fits inside it and a lid.
Water-bath canning is a lower-temperature canning process (212°F), which makes it safe ONLY for high-acid vegetables and fruits.
- High-acid foods include fruits, pickles, tomatoes, sauerkraut, relishes, jams, jellies, salsas, marmalades and fruit butters. It’s the acidity of these foods—in addition to time in a boiling water bath—which helps preserve them safely without the use of high pressure.
- High-acid fruits include berries and cherries, grapes, nectarines, oranges, peaches and plums.
- If it’s your first time canning, start with the boiling water bath method. Make some pickles or a berry jam.
Water-bath canning is not as big of an investment as pressure canning—and is more straightforward.
2. Pressure Canning
Pressure canning involves the use of a pressure canner, which is a device that consists of a large pot, a rack insert and a fitted lid with a dial or pressure valve. The high pressure created inside the canner when it is heated allows the temperature inside to get much hotter (240°F) than it could in a water-bath canner. This kills off any harmful bacteria, toxins, molds and yeasts.
Low-acid vegetables such as green beans or corn MUST be processed at a higher temperature to prevent the growth of bacteria, especially Clostridium botulinum. To maintain the higher temperatures for the proper length of time, you need to invest in a pressure canner which will get the job done.
- Vegetables that are low-acid include: artichokes, asparagus, carrots, corn, green beans, lima beans, mushrooms, okra, onions, peas, potatoes, pumpkin and winter squash.
- Fruits that are low-acid include: cantaloupe and watermelon.
Pressure canning is also used to preserve low-acid foods such as meats, poultry, seafood and chili which also require a higher temperature to raise the heat inside the jars above boiling and long enough to kill harmful bacteria. Pressure canning can be fun and satisfying, but it does require a canner to get started and you need to follow the directions closely.
If you’d like to preserve low-acid foods but don’t have access to a pressure canner, consider preserving them in other ways. Broccoli, corn and green beans taste much better when frozen, and they will have better texture when prepared using your favorite recipes. For best results when freezing, blanch the produce briefly in boiling water, remove and cool down quickly in ice water, drain and pack the produce in freezer bags or containers.
There are a few basic supplies which you’ll need in order to can at home:
- Canning jars, lids and screw bands: Only use clean jars without cracks or nicks in them. We recommend using the tried-and-true Ball brand mason or Kerr brand jars.
- Water-bath canner or pressure canner:
- For water-bath canning, it isn’t necessary to purchase a special water-bath canner as long as you have a pot that has a fitted lid and is large enough to fully immerse the jars in water by 2 inches—and that will allow the water to boil when covered. You’ll also need a rack that fits inside the pot or canner—a cake cooling rack would do.
- For pressure canning, only use a pressure canner made specifically for canning (Presto or All American) and not a pressure cooker.
- Jar lifter: Large tongs to move the hot jars in and out of the bolining water.
- Ladle: A ladle helps to spoon food into canning jars.
- Funnel: A wide-mouth canning funnel make it easier to fill your jars without spilling.
Where to Find Canning Supplies
Adams Fairacre Farms carries canning supplies so you can pick them up with some produce for canning! There are also many websites, hardware stores, craft stores and other retail outlets that sell kits that incorporate most of these canning essentials. Some also include other handy tools such as magnetic lid lifters, headspace-measuring tools, plastic bubble removers and jar scrubbers.
Except for single-use lids, which you must buy new every year, you can reuse mason jars, screw brands, the water-bath canner, food mill and stockpot for many years. You’ll often find these items in good condition at thrift stores, yard sales or in the basement of a friend or relative who’s given up on canning. If you find a nice canner with a domed cover but no rack, you can probably find one that fits your kettle in a local hardware store, farm store or online.
Make sure you check each jar, especially the rim, for small cracks or chips each time you use it. Also, don’t attempt to use a rusty canner.
Tips to Know Before You Start Canning:
- Always use fresh produce that’s in peak condition. Canning is not for overripe fruits or vegetables because they are on their way to spoiling.
- Gather all your ingredients and equipment and make sure you have everything you need before you start.
- Follow recipes and directions exactly. No improvising because your family’s safety depends on doing this correctly.
- Sterilize the jars by washing them well and then keeping them hot in a pot of boiling water until you are ready to fill them. Using the dishwasher will also get the job done without the pot of boiling water.
- Use real canning jars (Ball or Kerr), screw bands and new lids when you can. Lids on the market today do not need to be heated to activate the sealing compound before placing on the jar top.
- When you fill the jars, do not fill to the very top. This is called head space and can vary depending on your recipe (1/4 inch or 1/2 inch). If you overfill the jars, the food may interfere with the lid’s sealing compound and your jars will not seal properly.
- It’s important to wipe the jar rim and threads clean before putting on the lid and screw band. The band is tightened, but only finger tight.
- Using the jar lifter, place each jar on the rack in the boiling water. Make sure that the jars are covered by at least 1 to 2 inches of water, cover with lid and bring the pot to a boil. Start counting processing time once the water has returned to a boil.
- When processing time is done, turn off the heat and remove the lid, venting the steam away from yourself. Remove each jar with the jar lifter and place upright, 1 to 2 inches apart on a cloth towel to cool. Let jars cool 12 to 24 hours.
- One sign that your jars have sealed properly is a popping or pinging sound you’ll hear as the jars cool. Jars that don’t seal can NOT be stored but rather placed in the fridge and used within a few days.
- In general, your canned foods should last all year long, as long as they are stored in a cool, dry place. A broken seal is a sign air has gotten in. A bulging lid or a lid that seems corroded or rusty is also a sign of spoilage.
- When you do open your cans, if you ever see mold or bubbles or a cloudiness, that is a sign that the seal popped and it’s spoiled. Do not eat!
It’s important to know the food you’re planning on canning. More specifically, you need to know whether it is a low- or high-acid food, which dictates which canning method to use.
The biggest concern is botulism poisoning. Botulism is an illness caused by the botulinum toxin, which is produced by Clostridium bacteria. These bacteria occur naturally in soil and don’t usually present a threat to people. However, they are a very hardy type of bacteria and thrive in low-acid, low-oxygen environments, like those created when we can foods. When food is canned improperly, the bacteria grow and produce their deadly toxin, botulin, making the food unfit for consumption. It’s critical that the environment inside the canned goods is inhospitable to the bacteria by using high heat (240° F) for low-acid foods or by high acidity to inactivate any toxin present.
Information courtesy of Almanac.com