home canning

Home Canning, Food Safety, and Botulism

Home canning, food safety, and botulism—don’t freak out, but do process safely

By Diane Wright Hirsch


cold pack green beansAs an Extension educator, I have been teaching folks how to can for more than thirty years. And still, what worries folks the most is botulism poisoning. While it continues to be very rare, when it does occur, it is often associated with improperly home canned food. So, it makes sense to keep the possibility of this deadly toxin in the back of your head when canning.

In April of this year, a deadly botulism outbreak reminded us of how important it is to use methods for home canning that are tested for safety and recommended by science based resources. At a pot luck event at a church in Ohio, patrons were served potato salad that had been made from home canned potatoes. It turns out that the home cook had used a water bath process—which is inappropriate for low acid foods like potatoes. Twenty-nine cases of botulism were identified out of the 77 attendees. Twenty-five met the case definition and were given botulinum anti-toxin. One person died.

Botulism is caused by Clostridium botulinum bacteria. These bacteria live in the soil where we grow fruits and vegetables. In order to produce toxin, the bacterium needs an environment that is low in acid, moist, and free of oxygen. Therefore, this is not a hazard to foods that are safely canned in a water bath canner. Most fruits, pickles, and other properly acidified foods with a pH of less than 4.6 do not provide the environment conducive to toxin formation—they are too acidic. That is why these foods ARE safely canned in a water bath canner that reaches 212 degrees F during processing (or the boiling point of water).

Low acid or high pH foods (4.6 or greater) are another story. C. botulinum is a spore former. This means that when it is confronted with a hostile environment (heating in a canner), it forms a spore or coat to protect itself. This spore cannot be destroyed by temperatures at the boiling point of water associated with a water bath canner. If a water bath canner is used to can low acid foods, the spores will survive the heating, then they will germinate once the jar is placed on the shelf. These bacteria will then produce the deadly neurotoxin in the moist, oxygen free canning jar environment. Only a pressure canner can provide enough heat to destroy the spores—temperatures at 240 degrees F.

Home food processors need also to be reminded that they are not commercial processors. They do not have access to commercial equipment, additives and other processes that can render some food products safe from the botulism toxin. In addition, commercial processors must adhere to strict US Food and Drug Administration (FDA) rules and follow science based recipes and processes that they have proved-in advance of production-to be safe. So think twice before developing your own recipes for canning low acid or acidified foods at home.

Follow these basic rules for safe canning and there is no reason to fear botulism, home canning, or, for that matter, the use of a (preferably) newer model pressure canner, which has all sorts of safety mechanisms built in.

  • Jams, jellies and preserves are safely canned in a water bath canner. These products generally have a low water activity that contributes to safety and shelf life.
  • Fruits are generally acidic and safely canned in a water bath canner.
  • Spoilage organisms such as yeasts and molds can still be a problem in water bathed foods if not canned using methods tested for safety.
  • Tomatoes are a special case. They are often borderline in pH—sometimes exceeding 4.6. It is recommended that you add 1 tablespoon of bottled, commercial lemon juice or ¼ teaspoon of citric acid to pint jars or 2 tablespoons of lemon juice and ½ teaspoon of citric acid to quart jars as an “insurance policy” to ensure that the pH is low enough to process in a water bath canner. Current recommendations for water bath canners range from a 45-minute process (water added) to an 85-minute process (straight-up tomatoes)! It actually makes more sense to process tomatoes in a pressure canner—times are just about half that in a water bath.
  • Acidified foods such as pickles, pickled vegetables or fermented foods rely on the acidifying process to bring the pH to the range for safe canning in a water bath canner. (The addition of vinegar or the process of fermentation that creates lactic acid are examples of acidifying processes.) Be sure in this case to only use tested recipes. Never add a few more cucumbers or a bit less vinegar. You are risking raising the pH to levels that botulinum may find attractive.
  • ALL other foods MUST be canned in a pressure canner. Carrots, green beans, corn, and yes, potatoes; meats, fish, poultry; mixtures that might include tomatoes and low acid ingredients such as a meat sauce or spaghetti sauce with onions and peppers; and any foods made from these foods—soups, stews, etc.

Finally, keep in mind that home canned foods should never find their way into a commercial operation, retail store or restaurant. You cannot sell them in Connecticut, unless you are a farmer who can make and sell jams, jellies, and acidified foods such as pickles. And, it would be wise to ban them from church suppers, potlucks, bake sales and other similar volunteer food events. You just never know if a well-meaning home canner has followed the right directions.

For more information about safe home canning, visit the National Center for Home Food Preservation at www.uga.edu/nchfp or the University of Connecticut Food Safety web page at www.foodsafety.uconn.edu. You may also contact the UConn Home and Garden Education Center at 877-486-6271 or www.ladybug.uconn.edu.

Jam 101

By Diane Wright Hirsch, UConn Extension Educator, Food Safety

Photo: Clemson Extension


clemson jamOne of the best things about June in Connecticut is strawberry season. And we have been waiting a long time for strawberry season this year in Connecticut!  Most farmers will tell you that the cold spring and delayed picking as much as 2-3 weeks.  Even now, the supply is still gearing up.  Get to your farmers’ market early in the day if you want to score a box or two.  And be sure to check with your favorite pick-your-own (PYO) operation.  Some are just starting up this week.


Pick berries that are bright red and leave the overripe, mushy or those that are obviously headed in the wrong direction.  If you are planning to make jam or jelly, don’t think that you can get by with shoddy, overripe berries—you might end up with shoddy, over-mushy jam. A good rule to follow when it comes to preserving food at home—whether it is canned tomatoes, frozen green beans or strawberry jam:  you will never end up with a product that is of better quality than the produce (tomatoes, green beans, strawberries) that you started out with.


Refrigerate the berries as soon as you can after picking. Store unwashed berries loosely covered with plastic wrap in the coldest part of your refrigerator for two to three days at most. But, do not wash the berries before refrigerating them.  If washed, the berries are more likely to get moldy in your refrigerator.  Always wash them before eating, though. To wash, place berries in a colander and rinse under cold running water. Do not allow berries to soak in water—they will lose color, flavor and vitamin C.

Jam 101

If you plan to make strawberry jam, be sure you are following the most up to date guidelines.  Jam is made from crushed or chopped fruits and sugar. All jellied fruit products, jams, jellies, preserves, need to have just the right combination of fruit, pectin, acid and sugar in order to actually be “jellied.” 


Pectins are the substances in fruits that form a gel if they are in the right combination with acid and sugar. While all fruits contain some pectin, some have enough to form a gel on their own, while others, including strawberries, contain little pectin and the cook must use some commercial pectin in order to make a true jam or jelly. Because fully ripened fruit has less pectin, one-fourth of the fruit used in making jellies without added pectin should be underripe. That is why overripe fruit do not make good jams or jellies, they have less pectin and may result in a runny, under-gelled product.


The proper level of acidity is critical to gel formation. If there is too little acid, the gel will never set; if there is too much acid, the gel will lose liquid (weep).  Again, an underripe fruit may have less acid, preventing the gel from forming.  Commercial pectin products contain acids which help to ensure gelling.


Finally, there is the demon SUGAR.  Sugar serves as a preserving agent, contributes flavor, and aids in gelling. Many home cooks ruin a perfectly good product when they try to cut down on the sugar in a jam recipe.  Don’t do it! Too little sugar prevents gelling and may allow yeasts and molds to grow. Commercial low-sugar products are likely to use a different type of pectin (also available to the home cook) or sugar substitutes.  But really, how much jam do you eat?  It would be better to drink less soda, fewer candy bars, cookies or other commercially sweetened products and save your sugar calories for some home-made jams.


As a kid I remember the paraffin covered jams my mom used to make…and I also remember scraping the mold off of many of them.  But, research now shows that the mold we scraped off the surface of those jams and jellies may not be as harmless as it seems. Mycotoxins (or, mold toxins)  have been found in some jars of jelly having surface mold growth. Mycotoxins are known to cause cancer in animals; their effects on humans are still being researched.


Because of possible mold contamination, paraffin or wax seals are no longer recommended.  It is best to fill sterile jam or jelly style canning jars, leaving 1/4-inch headspace, seal with self-sealing lids, and process 5 minutes in a boiling-water canner. This little bit of extra work (actually, I think the whole paraffin thing was messier and more time consuming) will mean less chance of having to throw out the fruits of your labor.


For more information about safe handling of fresh-picked strawberries, contact the UConn Home and Garden Education Center at 877-486-6271 or the National Center for Home Food Preservationfor canning and freezing information.

5 Tips for a Successful Home Canning Season

Photo: PSU Extension
  1. Start with a research-tested recipe. Just because a recipe is in print, doesn’t mean it’s safe for you and your family. Start with a recipe that has been tested to make sure that the product is safe and high quality. A great place to begin is with the recipes from the National Center for Home Food Preservation www.uga.edu/nchfp/ Some states, such as Wisconsin, have recipe books that have been developed to ensure safe canning no matter where you live in the state: www.foodsafety.wisc.edu
  2. Use recipes that are up to date. We all want to continue with those tried-and-true recipes, but canning recommendations have changed dramatically over the last 15 years. If you are using recipes that date before 1994, then it’s a good idea to set those aside and find an up-to-date recipe that has been tested for safety.
  3. Start with equipment in good working order. A boiling water canner should have a flat bottom, so that it fits nicely on the stove top, and a tight-fitting lid. A pressure canner will have either a dial- gauge or a weighted gauge. Dial gauge canners should be tested every year for accuracy. Most county extension offices will test dial gauge canners for free! (This is certainly true in Wisconsin.) If you have a Presto dial gauge canner, contact the company if your county extension office does not offer this serve – 715-839-2232. Replace canner gaskets every 2-3 years. At this time, a steam canners is not recommended as a replacement for a boiling water canner. There is information to help you successful use your pressure canner: Using Pressure Canners www.uga.edu/nchfp/publications/uga/using_press_canners.htmlAnd one final note on canners, don’t use a pressure cooker, sometimes called a pressure saucepan, as a pressure canner. A pressure canner holds a minimum of 4-quart jars and has a pressure regulator capable of measuring up to 15 pounds of pressure.
  4. Assemble jars and other items. Use only standard home canning jars, not old mayonnaise jars, and check these to make sure they are not chipped or cracked. Always use 2-piece lids; purchase lids new each year (the sealing compound will break down on storage) and sort through screw bands to make sure they are not rusted. It’s fine to reuse canning jars, as long as they are not chipped or cracked. Garage sales can be great places to locate used canning jars, just make sure they were designed for canning. Other items that come in handy for home canning include jar fillers, tongs, and lid wands.
  5. Leave your creativity behind! Home canning is one area where being creative can lead to food safety disasters. So begin with an up-to-date, research-tested recipe and carefully follow the directions. Don’t make ingredient substitutions, unless they are allowed, and follow the recipe directions through all the steps. Don’t substitute dishwasher canning, oven canning, or open-kettle canning for an approved canning method – boiling water canning or pressure canning.

And remember, at the end of the day, a sealed canning jar does not indicate that the food inside is safe. A sealed jar simply means that the jar is sealed. You can do a lot of things wrong and still get a jar to seal! Follow these easy steps for safely preserving your garden’s bounty to enjoy all year round.

B. Ingham, May 2011, Wisconsin Extension

For additional information visit USDA’s National Center for Home Food Preservation.

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