Health

Botulism and Canning – What You Need to Know

shelves with canned food

Canning is a fantastic way to preserve food for when SHTF. While you can certainly buy pre-canned food, home canning can save you a whole lot of money, especially if you have your own garden.

Unfortunately, canning can be quite dangerous if done improperly. Indeed, botulism – a rare, yet potentially fatal disease – is a real concern for anyone that cans their own food.

Since something as simple as improper canning can lead to something as serious as botulism, you need to be sure that you’re preserving your food properly.

To help ensure you have the facts you need, up next, I’ll walk you through everything you need to know about botulism, from what it is to how to prevent it while canning your own food.

What Is Botulism?

Botulism is a serious and potentially life-threatening condition caused by the bacteria Clostridium botulinum. This bacteria is found naturally in soil and dust, where it exists in an inactive spore state that doesn’t do us any harm.

However, when C. botulinum is trapped inside a low-oxygen environment, such as a can or jar, it can produce a chemical poison.

Clostridium botulinum
An illustration of a photomicrograph of Clostridium botulinum.

This poison, known as the “botulinum toxin” interferes with our nerves and our muscles, and can cause paralysis either throughout the body or in certain muscle groups.

Botulism can be life-threatening because the botulinum toxin can paralyze the diaphragm.

The diaphragm is a large muscular structure that sits below our lungs and allows us to breathe. If our diaphragm is paralyzed, we cannot breathe and we can quickly die without medical intervention.

The Different Types of Botulism

When most people talk about “botulism” they are referring to just one form of the disease: foodborne botulism.

However, there are three types of botulism, each of which has a different cause. Here’s what you need to know:

Wound Botulism

Wound botulism occurs when the botulinum bacteria gets into a wound. When this happens, the bacteria can multiply inside the wound and produce the botulinum toxin.

While you could contract wound botulism from a regular cut or scrape, it’s not very likely. In fact, we see just 30 or so cases in the US each year. Additionally, the vast majority of wound botulism cases occur in people who use heroin.

Heroin (particularly black tar heroin) can contain botulinum spores, which can easily multiply after being injected into the body. That being said, the disease does not spread directly from person to person, and is very rare in the United States.

Infant Botulism

Infant botulism, as the name suggests, occurs in infants up to about 1 year of age. This disease happens when a baby ingests something contaminated with botulinum spores.

These spores then multiple inside the baby’s digestive tract and produce toxins that can be life-threatening.

Unfortunately, it isn’t clear what actually causes infant botulism. Many believe that infected honey or soil may be the culprit, but there is no conclusive evidence either way. Thankfully, infant botulism is very rare and we see just 70 cases each year in the US.

Foodborne Botulism

The third and final form of botulism is foodborne botulism. This form occurs when people consume food that has been contaminated with the botulinum bacteria.

This generally happens with canned food, since the botulinum bacteria needs a low-oxygen environment to produce its toxin.

We see just 25-30 cases of foodborne botulism in the United States each year. Interestingly, more than half of all reported foodborne botulism cases in the US since 1950 have occurred in five states: California, Colorado, Oregon, Washington, and Alaska.

Indeed, foodborne botulism is a public health issue within the Alaska Native population as it seems to be associated with the improper storage of traditional foods.

Since foodborne botulism is often caused by improper canning of foods, we’ll talk only about this form of botulism from this point forward.

As far as prepping and homesteading are concerned, foodborne botulism presents a real risk to anyone that is canning their own food. So, a proper understanding of the disease and how to prevent it is critical.

Signs and Symptoms of Botulism

Generally speaking, the signs and symptoms of foodborne botulism will begin within 36 hours after ingesting the toxin produced by the bacteria. However, this can vary depending on how much of the botulism toxin was actually consumed.

So, while one person might display signs and symptoms of botulism within 12 hours, it might be a whole day before another person starts to go downhill health-wise.

As with many diseases, botulism presents itself differently in different people. But, most people with the disease have signs and symptoms that include:

  • Dry mouth
  • Facial weakness
  • Drooping eyelids
  • Difficulty swallowing
  • Trouble breathing
  • Difficulty speaking
  • Vomiting
  • Nausea
  • Double vision
  • Abdominal Cramps
  • Blurred vision
  • Paralysis

How Is Botulism Treated?

According to Harvard Medical School, most cases of botulism require extended hospitalization. Since botulism is caused by bacteria, most botulism cases are treated with antibiotics, as well as an antitoxin, which directly works against the botulinum toxin.

If it is not caught early, botulism can lead to long term paralysis or disability. However, even when treated, botulism can still be fatal.

So, if you or someone in your family has symptoms of botulism, it’s essential that you seek treatment from a physician as soon as possible.

Botulism and Canning

Simply put, botulism is a scary disease that should be avoided at all costs. However, just because home canning can lead to botulism doesn’t mean we have to stop canning our food.

Rather, it means that we all need to understand both what increases our risk for botulism and how to can our food properly.

Why Proper Canning Is Important

A 2011 study found that out of 48 cases of botulism in the US that were linked to home-cooked foods from 1999-2008, every single one was caused by improper canning practices. According to the study:

Of the 48 outbreaks caused by home-prepared foods from the contiguous United States, 38% (18) were from home-canned vegetables.

[…]

In each instance, home canners did not follow canning instructions, did not use pressure cookers, ignored signs of food spoilage, and were unaware of the risk of botulism from consuming improperly preserved vegetables.

(Date et al., 2011)

Since botulism is a potentially fatal disease, it’s clear that anyone who wants to can their own food needs to know how to do so in an appropriate manner.

What Foods Can Lead To Botulism?

Thankfully, not all foods are prone to botulism. In fact, low-acid foods are the real culprits when it comes to home canning-related botulism poisoning.

What is a low-acid food, you might ask? Well, it’s any food that has a pH level greater than 4.6, according to the CDC. These foods are simply not acidic enough to prevent the growth of the botulism-causing bacteria.

According to the National Center for Home Food Preservation and the USDA, low-acid foods include:

  • Fish and seafood
  • All fresh vegetables
  • Beets
  • Figs
  • Some tomatoes
  • Potatoes
  • Milk
  • All meat products

When any of these foods are canned improperly, they create the perfect environment for the botulism bacteria to produce its deadly toxin. Indeed, the perfect environment for botulism to grow, according to the USDA contains:

  • Low-acid moist foods
  • Temperatures between 40ºF and 120ºF (4.4ºC-48.9ºC)
  • Low oxygen (less than 2%)

These conditions can easily be created when someone improperly cans any of low-acid food. So, it’s vital that we can our food properly and take the appropriate precautions to prevent this from happening.

Principles Of Canning

There are many different canning methods out there, so it can be tricky to figure out which one is best for your needs.

According to the National Center for Home Food Preservation, the canning method that you choose will depend on the acidity of the food you’re trying to can.

However, there are basic principles of canning that everyone should know, regardless of the canning method they choose.

In this section, I’ll briefly discuss the different concepts you should keep in mind before we start talking about different canning methods.

Overarching Principles

Before I get into different canning methods, here are some basic principles of canning that you should keep in mind whenever preserving food:

  • Low-acid foods (such as the ones I listed earlier) have pH values higher than 4.6. This means that they are not acidic enough to kill the botulinum bacteria on their own. Thus, we need to heat to ensure our canned food is safe to eat many months down the line.
  • You can acidify food using lemon juice, citric acid, or ascorbic acid. If you add an acidifier to a low-acid food, you can use slightly less heat in the canning process.
  • Acidic foods have a pH below 4.6. So, when these foods are canned, they can naturally kill off any botulinum bacteria. This means that acidic foods don’t require as much heat as low-acid foods – but you still need to heat them for a short period of time to destroy any other foodborne pathogens.
  • Botulinum spores are hard to kill. Some botulinum spores can survive boiling water temperatures. So, all low-acid foods need to be sterilized at a temperature of 240ºF-250ºF (115ºC-121ºC). This is possible with a pressure canner that’s operated at 10 to 15 PSI for 20 to 100 minutes, depending on the food.
  • The boiling water method generally takes longer. For low acid foods, the boiling water canning method can take between 7 and 11 hours. High acid foods can be processed through the boiling water method in 5 to 85 minutes.
  • Always start with high-quality food. When you can food, be sure that the products are that their peak-quality. This is generally within 6-12 hours of harvest for most vegetables. Home-slaughtered meat should be canned immediately. Seafood can be iced and canned within 2 days of harvest.
  • • Never can meat from sick animals. If you have meat from a sick or diseased animal it should never be canned. This can increase your risk for a whole host of foodborne illnesses.
  • • Store jars and cans properly. Always store jars and cans in a cool, dry, and dark place between 50ºF-70ºF (10ºC-21ºC).

The Importance Of Hot Packing

The National Center for Home Food Preservation also recommends hot packing your food. Hot packing is simply the process of heating up fresh food to a boil and simmering it for 2-5 minutes before placing it in a jar for canning.

Hot packing has the following advantages over raw packing (filling jars with unheated food):

  • Removes air from the food, which reduces spoilage.
  • Shrinks food so you can fit more in one jar or can.
  • Prevents food from floating in a jar or can.
  • Increases the vacuum seal of a jar.
  • Increases shelf life.
  • Prolongs the color and flavor of canned food.

Mind Your Headspace!

Additionally, it’s important to control the “headspace” of your jars when canning. The headspace of a jar is the space between the food and the top of the lid.

This headspace is critical for ensuring that there’s enough room in the jar for the food to expand in storage and processing without breaking the container.

The general guidelines for headspace in jars include:

  • 0.25 inches (6.35mm) for jams and jellies
  • 0.5 inches (1.27cm) for fruits and tomatoes in the boiling water method
  • 1 – 1.25 inches (2.54-3.18cm) for low-acid foods in the pressure canner method

Choosing the Right Jars And Lids

The last thing to keep in mind while canning food is the jar and lid that you’ll preserve your food in. For canning, you have two container options: metal cans and glass jars.

While metal cans are more durable than jars, they can only be used once, are costly, and require special sealing equipment. Jars, on the other hand, are readily available at most supermarkets and home improvement stores.

Jars come in a variety of sizes and in both wide-mouth and regular-mouth options. If you can your food carefully, you can reuse jars many times.

All you have to do is change the lid. While jars are glass and can break, this isn’t really all that common.

Whenever you use jars for canning, you should always wash and clean them with hot water and detergent.

Ensure that you’ve fully rinsed out any soap residue in the jar or you’ll end up with some weird tasting food a few months down the line.

Once your jars are washed, you can preheat them to prepare them for canning.

Preheating jars is quite simple and all you need to do is submerge them in a large stockpot full of simmering water. You can keep the jars in the simmering water until it’s time to fill them with food.

That being said, the washing and preheating process does not sterilize your jars.

If you’re going to can any pickled food, jams, or jellies in a boiling water canner, you’ll want to sterilize your jars first. To sterilize jars do the following:

  1. Wash the jars with soap and hot water.
  2. Place the jars right-side-up in a boiling-water canner.
  3. Fill the canner with enough warm water so that the water level is just 1-inch from the top of the jar.
  4. Bring the water to a boil.
  5. Boil the jars for 10 minutes if you’re at an elevation lower than 1,000ft (304m). If you live at a higher elevation, increase your boiling time by 1 minute for every 1,000ft (304m) of elevation.
  6. Reduce the heat once the boiling is complete. Keep the jars in the hot water until you’re ready to fill them.
  7. Remove one jar at a time and fill it immediately. Close the filled jars and place them back in the boiling water canner for the final processing of your food.

Keep in mind that you only need to sterilize your jars if you’re canning pickled food, jams, or jellies. Meats, vegetables, and fruits that will be processed in a pressure canner don’t need to be sterilized beforehand.

Additionally, you don’t need to sterilize your jars if you’re canning tomatoes, fruits, or fermented foods if you’re going to process them for more than 10 minutes in a boiling water canner.

Sterilizing your jars is only necessary for pickled food, jams, or jellies that are being processed using the boiling water method.

Proper Canning Methods

Now it’s time for the fun stuff: How to can food properly. As I’ve mentioned, there are different canning methods out there, each with their own advantages and disadvantages.

What’s important, though, is that you choose the right method for the food that you’re planning to can. Plus, it is vital that you follow the canning directions to the letter or you can risk botulism poisoning in your food.

As we learned from that 2011 study, foodborne botulism happens when people don’t can their food properly. So, don’t take shortcuts when canning. Additionally, if you don’t feel comfortable canning something at home, don’t do it.

You can probably buy professionally canned food in a store, which will also reduce your risk of botulism. With something as serious as botulism poisoning, it’s best to play things safe and not take any unnecessary risks.

With that in mind, here are three methods for canning food:

Boiling Water Bath Canning

The first method I’ll discuss is the boiling water canning method. As I’ve mentioned, this should only be used for acidic food or for low-acidic food that has been properly acidified with lemon juice, citric acid, or ascorbic acid.

To use a boiling water canner you will do the following:

  1. Halfway fill your canner with clean water for pint-sized jars. If you’re using larger jars, you will need more water so that there is 1-2 inches (2.54-5cm) of water above the top of the jars.
  2. Preheat the water. You’ll preheat to 140ºF (60ºC) for raw-packed foods. Alternatively, preheat to 180ºF (82ºC) for hot-packed food.
  3. Load the canner with your filled jars (with their lids on properly!) and ensure that they are covered with water. Keep the jars upright at all times.
  4. Set the heat of your stove to its highest position. Cover the canner with the lid.
  5. Heat the canner until you have a constant boil.
  6. Boil your containers for the appropriate amount of time, based on the jar size and your altitude. You can use the following chart as a guideline
  7. Add more water to the canner as needed to ensure the appropriate water level.
  8. After you have boiled your cans for the appropriate length of time, turn off the heat.
  9. Let the jars sit for 5 minutes and then remove them using a jar lifter.
  10. Place the jars on a towel and cool them at room temperature for 12-24 hours before placing them in storage.

Pressure Canning

If you’re planning to can low-acid foods, you’ll need to use a pressure canner. This is essentially a heavy-duty pot with a vent and pressure gauge that can heat your food to temperatures above boiling.

Since low-acid foods can’t kill off the botulinum toxin on their own, we need to heat them to a high enough temperature to prevent the bacteria and spores from growing.

To use the pressure canning method, do the following:

  1. Fill the canner with 2-3 inches (5.1-7.6cm) of water. You may need to use more water, depending on the food you’re canning. For specific advice, refer to the USDA’s guidelines.
  2. Place your filled jars into the rack inside the pressure canner using a jar lifter. Be sure to keep the jars upright at all times.
  3. Keep the weight off the vent port or open the petcock to allow steam to exit the canner.
  4. Put the canner on high heat and allow steam to exit the scanner for about 10 minutes. After, close the petcock or place the weight on the vent port to pressurize the canner.
  5. Once the dial gauge shows the recommended pressure, start your timer.
  6. As soon as your timer goes off, turn off the heat and remove your canner from the heat source to allow it to depressurize. Never force cool your canner because this can cause your food to spoil. The cooling and depressurizing process can take about 30-45 minutes, depending on the age of your canner.
  7. Once your canner has depressurized, open the petcock or remove the weight from the vent.
  8. Wait 10 minutes before opening the canner. When you lift the lid, be sure to keep your face well away from your canner so you don’t get burnt by the steam
  9. Remove the jars using a jar lifter. Place all of the jars on a towel and let them cool at room temperature. After 12-24 hours, you can put the jars in storage.

People often make mistakes when pressure canning. Generally, these mistakes fall into one of two categories:

  • Not hot enough. Since water boils at lower temperatures in higher elevations, you need to operate a pressure canner at a higher pressure at high elevations. This is why it’s important to consult a temperature chart, like the one in this article for the appropriate canning pressure for your location.
  • Too Much Air. If you trap a lot of air inside the pressure canner, it can throw off the gauge. If this happens, your food will be under processed and potentially dangerous. So, you must always vent your pressure canner for 10 minutes before starting the pressurizing process.

Dry Canning/Oven Canning Method

You will often hear people talk about “dry canning” their food. Dry canning is a process where you heat up your filled jars in the oven, instead of placing them in a pressure canner or boiling water canner.

This process is somewhat popular because it doesn’t involve any special equipment. With dry canning, you simply place your food in an oven at a temperature above 212ºF (110ºC).

However, the National Center for Home Food Preservation specifically states that it is not safe to dry can your food. Penn State University also lists dry canning as a method that is not recommended.

Other unsafe canning methods include solar canning, open kettle canning, microwave canning, and dishwashing canning.

The reason that oven canning is considered unsafe is because ovens produce a dry heat which is much more intense than anything a boiling water or pressure canner can create.

In this environment, glass jars can shatter in the oven or break in your hands as you remove them from the oven.

Other forms of dry canning are also unsafe because they can cause jars to explore. Additionally, many types of dry canning simply don’t heat up your food enough to prevent botulism or spoiling.

The Bottom Line

Botulism is a serious disease that is a real threat to anyone that cans their own food.

Ultimately, it’s best to only use canning recipes that follow the USDA guidelines for home canning, as these have been scientifically tested to prevent botulism in canned foods.

Additionally, it’s of the utmost importance that you follow every single step of the canning process to ensure you don’t accidentally underprocess your food.

While home canning can be a fun and rewarding process, it’s critical that you take the appropriate precautions to protect yourself and your family from the dangers of botulism poisoning.

botulism pinterest image

Gaby Pilson

About Gaby Pilson

Gaby is a wilderness survival expert, mountaineering guide, and professional outdoor educator, with specialties that include firearms handling and wilderness medicine. She is also a freelance writer for a variety of outdoor and survival publications.
View all posts by Gaby Pilson →

7 thoughts on “Botulism and Canning – What You Need to Know

  1. According to the Harvard study you quoted, this is what it ACTUALLY SAID (I put asterisks around the important words):

    “Of the 48 outbreaks caused by home-*prepared* foods from the contiguous United States, 38% *18* were from home-*canned* vegetables. *Three* outbreaks of Type A botulism occurred in Ohio and Washington in September 2008, January 2009, and June 2009. Home-canned vegetables (green beans, green bean and carrot blend, and asparagus) served at family meals were confirmed as the source of each outbreak.”

    Your article made it sound like all 48 cases were from home-canned food, and that is simply NOT what the study showed. Only 18 cases were from home-canned foods. The rest were from home PREPARED foods. I presume these foods were not properly cooked.
    Additionally, you can sterilize your canning jars in your dishwasher on the highest heat setting. Use them before the drying cycle starts.
    And, it is a pressure CANNER. (Number two in your instructions on how to properly uses a pressure canner,) You cannot use a pressure COOKER to safely can your goods.

    1. Thanks for pointing these out. I believe I confused Gaby when I asked her to use the study, thinking it was all about home canned food.

  2. I can’t read these long articles, but don’t reuse any Ball or Kerr brand of canning lids, I’m amazed people, do. I dry can rice and flour, in my Mason jars, I’ve yet to have on crack or explode on me tho, I do use lots of cation while doing this. I’ve opened up jars of rice that are 3 year’s old they are just fine, I would oven can meat, or vegetables, ever it’s only dry foods from the get go.

  3. Botulism is a Neuro-toxin. If you make it to the hospital and if your doctor knows what to look for and is willing to listen to you and if the anti-toxin gets to you in time you have a real chance of having permanent issues. This is one of the reasons I am amazed at the number of people who want to hold on to old canning habits and recipes.
    In a grid down situation this literally could kill you since there are only a few places to get the anti-toxin and you could easily need a ventilator.

    1. I think you’d be surprised by the number of households that still home can a LOT. Yet, the annual botulism number is extremely low, comparatively. E.coli and salmonella are also extremely dangerous and are found in grocery stores all the time in lettuce, spinach, peanut butter, and dozens of other prepared foods in the store. Not to mention restaurants! Knowing safe food handling is good and could be helpful, especially in this time when more people are gardening and likely more people will be resorting to tried and true methods of SAFE food handling.

  4. My comment is not about botulism, but the types of jars used. I’ve learned to use only Ball and Kerr jars in the pressure canner. I use the cheap knock offs like golden harvest from the dollar store only for hot water bath fruit or apple butter. It is such a waste when they break and what a mess. Not worth it to me.

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