We compare these two techniques of vacuum sealing homemade canned foods—and explain how to do each.
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Whether you want to preserve your summer bounty or save money on pantry staples, canning is an excellent skill to add to your kitchen repertoire. But if you're new to the practice, you might be considering the pros and cons of water bath canning versus pressure canning—or wondering if you need to bother doing either. Here, learn about the two different types of processing used to ensure homemade canned foods are properly vacuum sealed (plus, when to use each).

Quick Canning Methods vs. Extended Shelf-Life Techniques

If you make jam or jelly or pickles, transfer them to clean jars, and seal them, but don't process them using either water bath canning or pressure canning, you are making quick jam or quick pickles—also known as refrigerator jam or refrigerator pickles. Suchs food need to be stored in the refrigerator once cooled and used within three weeks; alternatively, they can be stored for up to a year in the freezer.

Why Water Bath and Pressure Canning Methods Make Food Last Longer

When homemade canned goods are properly processed using water bath or pressure canning methods, the air and food inside the jar expands, forcing air out of the jar. As the jar cools and the contents shrink, a partial vacuum forms, resulting in a state of negative pressure inside the jar. The sealing compound, found on the underside of the lid, prevents air from re-entering the jar. This ensures that no microorganisms can enter and contaminate the food. Ultimately, this gives homemade canned foods a much longer shelf life and means they can be safely stored in a pantry for up to a year until they are opened.

Water Bath Canning

Water bath canning is also known as boiling water canning or hot water canning. As these terms suggest, this method uses hot water to create airtight seals inside jars. The boiling portion destroys harmful microorganisms (like yeast, mold, and most bacteria)—except for Clostridium botulinum (C. botulinum), a bacterium that produces toxins responsible for botulism.

What You'll Need

Specifically, water bath canning uses a vessel called a water bath canner. The large, tall pot (made of aluminum of porcelain-covered steel) has a fitted lid and a stainless steel rack on the bottom. (If you already have the appropriate pot on hand, you can buy the rack on its own.) The purpose of the rack is to lift the jars away from the pot's bottom, and ultimately, the heat source. It also ensures each jar is completely surrounded by hot water.

How to Process Foods in a Water Bath Canner

During the process of water bath canning, jars of food are fully submerged in boiling water. They must be covered by at least one inch of water at all times—so if some of the water evaporates, you'll need to add more, notes Tracey Brigman, EdD, MS, RDN, LD, a clinical associate professor and associate director for National Center for Home Food Preservation at the University of Georgia. After the water has boiled for the required length of time, the jars will have an airtight seal.

Pressure Canning

Whereas water bath canning uses heat from boiling water to kill microorganisms, pressure canning relies on the germ-killing power of pure steam and is slightly more involved: It uses physical force, or pressure, to seal jars. It's worth noting that pressure canning is different from pressure cooking, and pressure cookers should never be used for canning.

What You'll Need

The method requires specialized equipment, including a pressure canner, which looks like a kitchen pot with extra features. According to the United States Department of Agriculture, this includes parts like an automatic vent or cover lock, a steam vent, and a gauge; it also consists of a jar rack that's placed inside the pot.

How to Process Foods in a Pressure Canner

The pressure canner should be filled with few inches of hot water, followed by the jar rack and lid. The canner is then heated on the stovetop, which causes the water to produce steam. As steam accumulates, the temperature and pressure in the canner increases. This high temperature—which is higher than what's achieved in water bath canning—and high pressure is what destroys harmful microorganisms and seals the jars.

Once the canner achieves the right pressure and processing time, the heat is turned off and the canner is depressurized, says Brigman. This can be done using the steam vent, which is built into the canner.

How to Choose the Best Canning Method

When deciding between the different types of canning methods, the best one will depend on the specific food you're preserving. The reason? Different foods have different levels of acidity, which determines their risk of becoming contaminated with C. botulinum. This type of bacterium is resistant to heat, but it can be destroyed by acid.

Process Low-Acid Foods in a Pressure Canner

As Brigman explains, low-acid foods (those that have a pH higher than 4.6) should be processed in a pressure canner. Due to their low acidity, these foods have a higher risk of C. botulinum growth—so they'll need to be processed at the higher temperatures achieved in pressure canning.

According to the USDA, examples of low-acid foods include red meats, seafood, poultry, and all fresh vegetables (except for most tomatoes). These foods can also be made more acidic with the addition of lemon juice, citric acid, or vinegar.

Process High-Acid Foods in a Water Bath Canner

High acid foods (that have a pH of 4.6 or lower) are a different story. The acidity of these foods can block or kill C. botulinum, so they don't need to rely on heat to get the job done. In turn, they're more appropriate for water bath canning—which, again, involves lower temperatures than pressure canning.

Examples of acidic foods include fruits, pickles, jams, and jellies. Tomatoes and figs are also acidic and fall into this category, but some have a pH above 4.6 (so they're less acidic). In this case, they'll need to be acidified with lemon juice or citric acid before being processed in a water bath canner, per the USDA.

Follow a Recipe

Regardless of the food or canning method you're working with, it's important to follow a tested recipe from a trusted source, explains Brigman. "Many of today's canners are interested in being creative, but the maintenance of safe practices in canning [is so important]," she says. "Recipes should be followed as written."

Using the proper equipment and adjusting for altitude is also crucial for food canning safety, Brigman adds. All that said, if a food is improperly canned, it can create the right conditions for C. botulinum to flourish and make the toxin that causes botulism, notes Brigman. For the best results, always follow a recipe exactly as written.

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