All You Ever Wanted To Know About Open Kettle Canning But Were Afraid To Ask

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By and large, discussing open kettle canning, also known as inversion canning, in a canning community can lead to intense online debates, resembling a virtual battleground. It is not uncommon to have opposing sides exchange harsh words whenever somebody brings up the subject of canning the old fashioned way. However, safety arguments on both sides are often superficial, boiling down to phrases like “because our ancestors did it” or “because the USDA recommends it.” With our background in medicine and applied science, we diligently examine safety concerns related to open kettle canning, exploring the reasoning behind each argument. Subsequently, we’ll offer practical steps aimed at enhancing the safety of your open kettle canning practices.

Disclaimer and Caution

Without reservation, we state that the open kettle canning method is not an approved USDA canning method to preserve food. The information shared here is for general awareness and personal use only. Equally important, we acknowledge that the provided information may contain inaccuracies or errors, and we explicitly disclaim liability for any such inaccuracies or errors to the maximum extent permitted by law.

What is open kettle canning method?

The open kettle canning method, frequently referred to as an old way of canning, is a way of preserving food the old fashioned way. It involves cooking a preserve in an open cooking dish, commonly known as a kettle (usually a pot of suitable size). Subsequently, the process requires the canner to pour the boiling food into sterilized jars, secure them with lids, and finally invert the jars to cool. The seals in this method are created by a vacuum as the jars cool in the inverted position. This is the reason why this method is known as the inversion canning method.

Historically, open kettle canning or inversion canning was considered safe until the 1980s (source: National Agricultural Library Exhibits, U.S. Department of Agriculture). Anecdotes suggest that individuals who have lived through that era still recall respected experts in the field of canning actively endorsing the open kettle method before its safety status changed.

What is botulism?

When people discuss open kettle canning, botulism in canning inevitably becomes a central topic. But what exactly is botulism? Simply put, it’s a rare but severe and sometimes fatal illness caused by a toxin produced by a specific type of bacteria. Markedly, botulism bacteria grow in a moist, oxygen-free environment, a reason why improper home canning can provide ideal conditions for it to multiply and produce the toxin.
So, how widespread is botulism?

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By all accounts, it is a relatively small number.

Botulism types

Did you know that botulism from canning, also known as food-borne botulism, is not the only way to get sick with this disease?

Out of the 242 cases of botulism reported to CDC in 2018:

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Across the border:

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While cases of food-borne botulism may be relatively rare, the impact on families or individuals can be significant. Despite the seemingly low numbers, why risk a potentially fatal disease when there are ways to prevent it?

Where does botulism come from?

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Food and beverages become contaminated when spores of the bacteria that cause botulism get into these products. These spores may be able to grow into toxin-producing bacteria in low-oxygen low-acidity environment.

The botulinum toxin has been found in a variety of foods, including low-acid preserved vegetables, such as green beans, spinach, mushrooms, and beets; fish, including canned tuna, fermented, salted and smoked fish; and meat products, such as ham and sausage. Occasionally, commercially prepared foods are involved.

The good news about botulism from canning

While botulism is a horrible disease, at least as far as foodborne botulism, not all is gloom and doom. According to WHO, the good news is:

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The reason why this is good news is that whatever canning method you use, including open kettle canning, as long as the foods you preserve do not fall under the low-acid category, the last thing you should worry about is botulism from canning. You should still worry about other canning-related things, but botulism isn’t one of them.

Why does USDA no longer consider open kettle canning safe?

USDA National Agriculture Library said this about open kettle canning:

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Furthermore, in August 2020, the USDA emphasized the increased risk of food spoilage as the reason for not recommending open kettle canning. They explicitly caution against practices such as open-kettle canning and processing freshly filled jars in conventional ovens, microwave ovens, and dishwashers, as these methods do not effectively prevent all risks of spoilage.

What does USDA say about botulism in canning?

The USDA explicitly associates the risk of botulism with canning low-acid foods. Importantly, this risk isn’t exclusive to the open kettle canning method. Even the USDA-approved water bath canning method gets the same warning sticker when it comes to canning low-acid foods. The USDA emphasizes that the only secure way to can low-acid foods is by using a pressure canner. Severe cases of foodborne botulism have even prompted an OSU Extension educator to emphasize that using the wrong canning method, such as a boiling water bath, can lead to botulism in low-acid canned foods like meat, potatoes, and vegetables.

To summarize, it’s not accurate to say that the USDA links old fashioned canning to botulism, irrespective of whether you are trying to preserve low-acid or high-acid foods. When low-acid foods are removed from the discussion, the USDA’s main concerns with the old fashioned canning methods are:

• Increased risk of contamination while pouring and sealing jars
• Increased risk of spoilage

Canning low-acid foods

They say the best prevention is avoidance. If you are not planning to use a pressure canner to can low-acid foods, the wisest approach may just be to stay away from caning these foods.

Wondering what foods are low in acid? Many years ago, USDA put together a useful drawing that still can be used today as a guide:

However, because WHO already told us that the botulism bacteria will not grow in acidic conditions, especially in combination with higher salt contents, increasing acidity and saltiness in the low-acid foods may just be your ticket to success. The next question is how to figure out the acidity level of your preserve.

How to measure food acidity levels

Determining the acidity level of preserves requires using pH measuring tools, either pH strips or pH meter. While pH strips offer a cost-effective and simple to use option, they lack accuracy and precision. On the other hand, pH meters, though more expensive significantly more complicated to use, provide accurate readings.

How to avoid contamination of preserves when using open kettle canning method?

So, say you decided that canning low-acid foods is not for you but you plan to continue canning jams, jellies, pickles and the other acidic foods. Lets say that for canning these types of food, you plan to continue canning the old fashioned way but are concerned about the increased risk of contamination during the pouring and sealing steps. This is how you can minimize that risk:

• Firstly, make sure to keep everything clean and hygienic throughout the entire canning process. Wash your hands thoroughly with soap and water before touching any ingredients or equipment. Also, ensure that all surfaces, utensils, and containers are disinfected to get rid of any potential contaminants. Cleaning with a sponge that’s been sitting in your kitchen sink for a month won’t cut it; use disinfecting products like Clorox to kill harmful bacteria.
• Secondly, when using mason jars, pots, and other canning equipment, clean them in a dishwasher or with hot water and soap. After careful cleaning, make sure to sterilize mason jars, funnels, and ladles. We discuss sterilization details in a separate post.
• When preparing preserves, throw away any bruised or damaged produce, as they can carry harmful microorganisms. Wash fruits and vegetables under running water to remove dirt and debris. Peel, core, and cut them with clean utensils on sanitized surfaces only.
• Speaking of sterilization, make sure to sterilize your jars by boiling them in water or steaming them over boiling water (steam sterilization). Additional sterilization details for jars are provided in a separate post.
• Also, sterilize all of your utensils by submerging them in boiling water for up to 5 min. We recommend to use stainless steel utensils. Remember that a sterilized ladle stops being sterilized once it touches a counter casually wiped with an old kitchen towel instead of being disinfected.
• It’s worth noting that when reaching for a paper towel that’s been collecting dust on your counter for a couple of days to clean jar rims, you might introduce bacteria into your preserves. Dip the paper towel into boiling water with sterilized kitchen tongs before wiping jar rims with a wet paper towel.

How to decrease the risk of preserve spoilage when canning the old fashioned way

If you’ve followed our tips to keep your preserves safe, you’re on the right track to reduce the chance of them going bad. To set the record straight, we are not talking about botulism bacteria. Contamination with botulism-causing bacteria won’t make your preserves smell weird or look different. However, there are other bacteria that, although not that deadly, can upset your stomach. Ever seen black and white moldy patches on preserves? How about the jars with bulging lids or even leaking a bad-smelling liquid? That’s the kind of bacteria we’re talking about!

• Firstly, just like with water bath canning, using heat to process your preserves further lowers the risk of spoilage. However, in open kettle canning, the way to keep the preserve temperature high inside the jar for a longer time is by means of wrapping jars in two to three thick beach towels.
• Additionally, an important step in decreasing the risk of spoilage is to ensure that your canned preserves have a reliable seal. With an open kettle canning method, the seal is created as a result of inverting jars packed with preserves and letting them cool upside down.

Both of these steps are essential to ensure the safety of your preserves for you and your family if you choose to continue using the traditional canning method.