Featured, Food, Outdoors, Science

Home Preserving And Botulism: When to Worry (And When Not to!)

By Allison Sayer for Seward City News-

Disclaimer: Seward City News is not responsible for any illness including botulism incurred by readers canning food. Readers should consult with experts and professionals such as the Cooperative Extension before attempting home canning projects.

I have had many people tell me they would love to do their own preserving, but they are afraid of poisoning themselves and the people they love. This is a legitimate concern. Botulism is a serious disease caused by a toxin that can be found in improperly canned foods. Unfortunately, the toxin has no smell, taste, or appearance. You will not know by examining the food whether it is present. Fortunately, scientists have learned enough about the botulism toxin to teach us how to avoid creating it in the first place.

Know thine enemy: What is Botulism?

Photo: US Department of Agriculture.

If you have botulism, it means you have consumed a high enough level of the botulinum toxin to affect your nervous system. The toxin is produced by a few specific bacteria species, most commonly Clostridium botulinum. It destroys communication between your brain and your muscular system. Symptoms include palsies, paralysis, and even breathing failure from a neurologically impaired diaphragm. It is treatable, but recovery can be lengthy and some patients die.

The bacteria that produce the botulinum toxin are actually extremely common. There are likely to be some around you right now. But, in general, the bacteria remain encapsulated in spores and they are not actively reproducing or producing toxin. In certain conditions, the bacteria have the potential to grow and to produce toxins. These are the conditions you want to avoid.

The bacteria grow and produce toxin in an anaerobic, low-salt, low-acid environment. “Anaerobic” means “without oxygen.” That is why canning in particular is associated with botulism. Therefore, a lot of the “rules” of canning are meant to either kill the bacteria or create an environment in which the bacteria can not grow.

The bacteria also require temperatures between 4 and 121 degrees C (39.2 and 120 degrees F), and some time to grow. That is why you don’t have to worry about getting botulism from frozen foods, and typically not from refrigerated foods.

Killing the bacteria: A Pressure Cooker is the Only Way

If your food is NOT acidic, and you are NOT going to store it in the freezer, you must kill the bacteria. The foods that typically fall into this category are unpickled vegetables, beans, fish and meats. Since C. botulinum spends much of its life encapsulated in very tough spores, it is very tough to kill. The spores can survive being boiled even though most bacteria can not. The pressure cooker raises the temperature to above the normal boiling point of water by changing the pressure within the pot.

When you use a pressure cooker to can foods, you must follow the instructions completely. You must make sure any botulism causing spores are exposed to high enough temperature for a long enough time to be killed. Many people are intimidated by pressure cookers, but the reality is they are quite easy to use.

Over time the gauges on pressure cookers can wander. Your local Cooperative Extension can test your gauge for free.

Fruit: Naturally Acidic

Salmonberry. Photo: Andrea Moreno-Beals


C. botulinum requires a pH above 4.6 to grow. (Remember- lower pH means more acidic).

The great news is that rhubarb, fruit, berries, and berry juice are naturally acidic. That is why you do not need to use a pressure cooker to make fruit preserves. Fruit preserves need to be preserved properly to avoid mold, poor seals, spoilage, and contamination from other bacteria. However, botulism is not a concern.

Pickles: Foods You Make Acidic

Pickles. Photo: Ben Mason.

Pickles are different from fruit because they are made from vegetables that are not inherently acidic. The pickling process is what creates the salty, acidic environment in which botulism can not grow. This is where things get tricky, and it is really important to understand what you are doing to avoid making a dangerous product.

The salt and acid content has to be high enough for pickles to be safe. It is really important to get your recipes from a reputable source because these recipes have been tested.

Cooperative extensions, pressure cooker companies, canning companies, and industrial food producers publish recipes for pickling. The people who created these recipes understand the science behind botulism. They repeatedly tested the final products’ pH and got safe results.

Be wary of internet recipes. Not every random person on the internet understands science. 

What about your grandmother’s recipe? If you want to use a recipe that hasn’t been tested, you have a couple of options. You can test the pH of the final product with a home testing kit or take it to a university or cooperative extension office. Remember: Botulism tends to grow in foods stored at room temperature over time. If you are not sure whether your pickles are safe for long term storage, you can refrigerate them and eat them promptly. 

If you do have a tested, trusted recipe, you need to follow it exactly. If you start improvising, you could change the pH of your pickle jar. 

Infused Oils: A Little Known Risk

Home made infused oils made from fresh herbs or fresh garlic can carry a risk of botulism. However, these oils are delicious and much more affordable than store bought. Time and temperature are your friends to keep these oils on the safe side.

I make these oils all the time, but I do not store them for a long time. I make small amounts, date the jars, and use them within a couple of weeks. If you would like to make large batches, you can store the majority of your oil in a freezer, then use it promptly after it has been thawed. Never let a home made infused oil sit in your cabinet for months or years.

Stay on the safe side

Canning is Fun! Photo: Allison Sayer

Canning is a lot of fun. You can make incredibly delicious treats and (sometimes) save money. Just follow the science and don’t skip steps. Remember, you can not tell from looking at a food whether it contains the botulinum toxin. So, the most important rule is: “If in doubt, throw it out.”


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