Perhaps the biggest concern of any home canner should be how to avoid botulism. Botulism is an illness that can affect your nerves, cause paralysis and even result in death. It is a medical emergency that requires immediate care. You cannot see, smell or taste botulism.

My purpose here is not to scare the pants off you, but to compel you to use the correct home canning methods and processing times. If you know why the canning instructions have specific methods and processing times, you are less likely to cut corners or experiment. But fear not – home canning has been done for decades with success, so if you are armed with a little knowledge and follow the proper protocols you will be successful, too!

What is botulism?

Botulism comes from a germ that lives in soil, and its spores are on most fresh foods that we eat. The spores are harmless, except under certain conditions. The spores can only produce vegetative cells, which in turn produce the deadly toxin, in the absence of air. Under the right conditions, the cells can multiply very rapidly. Because canning severely reduces the amount of air present, you can see why improperly canned foods can be a real danger.

You can reduce the number of microorganisms on fresh food prior to canning by removing the outer skin with a peeler and/or blanching the food, but the best and most vital way to prevent contamination of microorganisms in canned foods is to use the proper canning method and process the jars for the correct amount of time. In order to do that, you need to know whether the food you are canning is high acid or low acid.

High Acid and Low Acid Foods

High acid foods can be canned using the common water bath method, but low acid foods need the added heat of pressure canning to prevent the growth microorganisms. The acidity of different foods is what helps to keep these in check, and low acid foods do not have enough acidity.

A word of caution: When finding your recipes, particularly online, or when mixing foods with high and low acid levels for canning recipes, be sure to follow instructions from reputable sources. A random recipe found online is not as trustworthy as say, a recipe from the USDA or one of the top canning jar manufacturers. A reputable recipe source could also be one that has been used successfully in your family for years. There are some links at the end of this post to reputable information.

In general, your high acid foods will be fruit, pickles, sauerkraut, jams, jellies, marmalade, and fruit butters. Your low acid foods will be red meats, seafood, poultry, milk, and all fresh vegetables except for most tomatoes. Tomatoes like to live on the edge between being high and low acid. Tomatoes are considered a fruit, but some types are now known to be less acidic than others.   Another reason to follow instructions from reputable sources.

Acidity Determines Canning Method

High acid foods, by virtue of having more acid to keep the nasties away, can be canned safely using the water bath method. This method is the oldest in home canning. Basically, you use hot food packed in sterilized jars, sealed well and immersed in boiling water for a specific amount of time.

Water bath is the method taught to me by my Mother and Grandmother. They used the water bath method to can all of their vegetables. No one got sick or died of botulism in my family, even though the current recommended method of canning for vegetables is pressure canning. However, the more we know, the safer we are – I no longer use water bath canning for my vegetables.

Low acid foods should be canned using the pressure canning method. Pressure canners get up to higher temperatures than boiling water, and so can kill the nasties without the help of food acidity.  When using a pressure canner, be sure to read and follow all of the instructions to be accident free. Pressure canners work by building up pressure in the unit and can be dangerous if instructions are not followed.

How to Know if Canned Food is Unsafe

There are some telltale signs of unsafe canned food. If any of the following are even the slightest concern to you, throw it out! Never taste food to determine if it is safe. It only takes a small amount to cause you a world of trouble.

Signs that your home canned food has spoiled:

• the seal on top of your canned jar has popped up
• when opened, the food is discolored, smells bad or is moldy
• the jar or container is leaking, bulging or swollen
• it spews liquid or foam when opened
• the jar looks cracked or otherwise damaged

According to the CDC (Centers for Disease Control), contaminated food spills and leakage should be cleaned properly.  Spills and leakage should be cleaned with a solution of 1/4 cup bleach for every 2 cups of water.

Now that you know why the correct canning method and processing time is important, I believe you will be highly successful at preserving your delicious homegrown food. Opening a jar of your summer produce in the middle of winter is one of life’s greatest joys!

Additional resources:

USDA’s Complete Guide to Home Canning : This is hands down the best, most complete and up-to-date resource I have found. Safe instructions for canning virtually anything with printable files!

Recipes from Ball Jars : Exceptional selection of canning recipes.

Canning Foods – the PH Factor :  More in depth information regarding the acidity levels of foods. Lists foods and their specific PH levels.

Home Canning and Botulism : A link to the CDC’s information on this topic. Includes symptoms of botulism poisoning.