Unsafe Techniques When Canning at Home

Unsafe Techniques When Canning at Home

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-by Patrice Lewis Canning is one of the most versatile, safe, and historically significant food preservation methods to arise in the past 200 years. But it has a flipside: it can be among the most dangerous, especially when canning at home.

Botulism is a real risk when canning at home.

The biggest danger from canning at home is the risk of botulism due to improper canning techniques. Botulism is caused by a toxin produced by the bacteria Clostridium botulinum, which attacks the nerves and can be fatal. Botulism is nothing to mess around with, which is why proper canning techniques MUST be followed.

Below are several techniques that should always be avoided when canning at home.


Water-bath canning low-acid foods.

Some people mistakenly believe that if they water-bath can low-acid foods for a long enough time (instead of using a pressure canner), then the food is rendered safe. This is wrong. Low-acid foods MUST be pressure-canned following proper procedures.

Oven-canning food.

Oven-canning is a procedure by which jars are filled with food, then baked in the oven on the theory that oven heat will kill pathogens and render the food safe. This procedure is dangerous and ineffective. Oven temperatures do not penetrate the interior of the jars sufficiently to kill botulism.

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Using the Open-kettle method when canning at home.

This is the process of merely placing hot food in jars and capping the jars with no further heat treatment. This does not preserve the food. There is no substitute for adequate heat treatment when it comes to canning at home, and open kettle canning doesn’t provide that.

Microwave-canning.

Because a microwave can only reach 212 degrees Fahrenheit — and because it heats in an uneven pattern — it doesn’t provide sufficient heat to each jar to render pathogens harmless. Low-acid foods must be heated to 240 degrees F (only possible in a pressure canner), and even high-acid foods must have the uniform heat provided by a water-bath to be rendered safe. Microwave canning is just as dangerous as open-kettle canning.

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Dishwasher canning.

The water temperature in a dishwasher is far below that needed to kill harmful pathogens. Any food products (whether low-acid or high-acid) will be under-processed and unsafe.

Slow-cooker canning.

Similar to the open-kettle method, food is heated in a slow cooker, then placed in jars and capped with no further processing. This is a
dangerous and ineffective practice of canning at home.

Solar canning at home.

Using the sun’s heat to warm up a box in which jars are placed for processing is almost a comically ineffective method of canning. Don’t do it.

Guesswork canning.

Some people don’t follow proper preparation or processing methods and times, including altitude adjustments, and merely “guess” how long something should be processed. Under processing a food product, either with inadequate pressure or incorrect length of time in the canner, is a
recipe for botulism.

Canning in half-gallon jars.

Decades ago, it was routine to process foods in half-gallon jars until it was
discovered that heat could not sufficiently penetrate the interior. Half-gallon jars should not be used for either water-bath or pressure canning. The exception is apple or grape juice, which is thin enough for heat to
penetrate.

Canning powders (or canning pills).

Once touted as a catch-all solution, these salicylic acid (aspirin) tablets
were dropped in each canning jar before it was capped as a preservative. It has long been proven that these are useless as a preservative and don’t replace heat as a processing method.

Outdated equipment.

One-piece zinc porcelain-lined caps, zinc caps that use flat rubber rings, or jars with wire bails and glass caps should only be used as decorative antiques, never for food processing.

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Some foods aren’t safe for canning at home.

In addition to unsafe canning techniques, some foods are unsafe to can at home. These include:

Foods packed in oil.

Canning in oil isn’t recommended because oil coats and insulates botulism
spores and creates a micro-environment which allows the spores to survive high heat. To kill botulism spores encased in oil would require pressure canning at such high temperatures and for so long that the food itself would be destroyed. (A small amount of oil, for example sautéing before canning, is acceptable if it has been factored in and present at the time the processing time for the food was researched.)

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Highly viscous foods should be avoided when canning at home.

Items such as refried beans, peanut butter, pumpkin purée, or squash purée should not be home-canned. (Cooked cubed pumpkin can be canned at home, but cubed summer squash will compress during heating and become too thick; it shouldn’t be home-canned.)

Lard.

This is too dense and too fatty to safely can at home.


Pickled eggs.

There are no safe, tested recipes for canning pickled eggs.

Dairy products aren’t safe for canning at home.

Soups (or other foods) made with cream, milk, butter, or other dairy products are not recommended for home-canning. Dairy products are
low-acid and support an environment which fosters botulism. The fat in dairy products can protect botulism spores and toxins from heat during the canning process. When milk is over-heated, the milk proteins drop out of suspension and separate. The amount of heat needed to kill botulism is so extreme that the food would be rendered inedible. For this reason, canning milk or canning butter isn’t recommended as a safe procedure for home canners.

Cornstarch.

This thickener breaks down during processing and may present quality problems; more importantly, it retards heat penetration. The USDA doesn’t have any tested procedures for cornstarch. The recommended thickener is Clear-Jel, which is a modified corn starch formulated for canning. Clear- Jel does not break down in acid food mixtures, and it doesn’t thicken so much that it interferes with heat-killing of pathogens.

Flour.

Some people believe they can make “cakes in a jar” or other foodstuffs which contain flour. This is strongly inadvisable. Home-canned flour products (breads, doughs, etc.) are considered very prone to botulism. No one has yet been able to come up with a reliable recipe and canning direction that doesn’t produce botulism some of the time. Flour products are most often low-acid, and “baking” them in a jar is not “canning” and is not recommended.

But … Granny did it when canning at home!

One of the most frequent arguments is, “But Granny always canned her green beans/chicken/corn/spaghetti sauce in a water bath. None of us ever got botulism.” Remember, past performance does not guarantee future results. If Granny never killed anyone through botulism, she was just lucky.
There will always be people who think the rules don’t apply to them when canning at home, or believe they’re special enough to refute the science behind safe canning.

Canning is a highly developed science, and to assume the rules don’t apply to you is asking for trouble. Be safe, and happy canning!


Originally published in the September/October 2023 issue of Countryside and Small Stock Journal and regularly vetted for accuracy.

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