Two Letters Re: The Joy of Canning

I read with interest DDR’s article “The Joy of Canning”. Most of her advice is spot-on and an excellent primer for new canners. I commend her for such a comprehensive article for novice canners. However, she includes some potentially dangerous advice that can invite the risk of botulism. For example, she correctly writes, “Vegetables and meats are considered low-acid and should always be processed in your pressure canner. This is also true of your soups, chilis, and most sauces. I find that it’s a good idea, when in doubt, to pressure can just to be safe.” Then, she contradicts this advice later in the article when she writes, “By the way, I water bath can my spaghetti sauce, even though it contains onions, peppers, and oil, because tomatoes are so very high in acid.”This is INCORRECT. If her spaghetti sauce contains onions and bell peppers, then the food MUST be pressure canned in order to prevent the deadly disease of botulism. The acid in tomatoes does not negate the fact that onions and bell peppers are low-acid and must be pressure canned.

The rule of thumb for canning mixed-ingredient foods is to PROCESS THE FOOD IN ACCORDANCE WITH THE INGREDIENT REQUIRING THE LONGEST PROCESSING TIME. In this particular case, bell peppers canned in quarts require processing for 45 minutes at 10 lbs of pressure (adjusted for altitude). Pressure canning these low-acid ingredients for less time or water-bath canning them invites the risk of botulism.

Even without the addition of low-acid ingredients, sauces made with modern, hybrid tomatoes are often too low-acid to be safely canned in a water-bath. It is recommended that citric acid or another acidifier be added to increase the acidity in order to safely water-bath can. And as I mentioned, if there is anything else added to the sauce (such as bell peppers or onions), then the sauce MUST be processed in accordance with the ingredient requiring the longest processing time.

DDR also mentions canning butter or high-oil items, both of which are items that should not be canned at home. While DDR claims she’s never poisoned anyone yet, I’d like to remind her that “past performance does not guarantee future results.” There are some things that home canners shouldn’t can at home, even with a pressure canner, and even if those products are available commercially. Commercial canneries have additives, preservatives, and processing controls that are not available to home canners. They also have professional processing equipment that we can’t duplicate at home.

The foods not recommended for home-canning include:

  • Foods packed in oil. Canning in oil is not recommended because oil coats and insulates botulism spores and creates an anaerobic micro-environment, which allows the spores to survive high heat. To kill botulism spores encased in oil would require pressure canning at such high temperatures and for so long that the food itself would be destroyed. (A small amount of oil, for example used in sautéing before canning, is acceptable.)
  • Highly viscous foods. Items such as refried beans, peanut butter, pumpkin purée, or squash purée should not be home-canned. (Cooked cubed pumpkin can be canned at home, but cubed squash will compress during heating and become too thick; it should not be home-canned).
  • Lard. It is too dense and too fatty to safely can at home.
  • Pickled eggs. They are too dense to safely can at home. There are no tested recipes for canning pickled eggs.
  • Dairy products. Soups (or other foods) made with cream, milk, butter, or other dairy products are not recommended for home-canning. Like oil, dairy products are low-acid and support an environment which fosters botulism growth at room temperature. The fat in dairy products can protect botulism spores and toxins from heat during the canning process. When milk is over-heated, the milk proteins drop out of suspension and separate. The amount of heat that would need to be used to kill botulism is so extreme that the food would be rendered inedible. For this reason, canning milk or canning butter is not recommended as a safe procedure for home canners.
  • Cornstarch. Cornstarch is a thickener that breaks down during processing; more importantly, it retards heat penetration. When a thickening agent is needed, use Clear-Jel, which is a modified corn starch formulated for canning. Clear-Jel does not break down in acid food mixtures, and it does not thicken so much that it interferes with the process of heat-killing any pathogens. Please note that processing times listed in published reference books are not sufficient for using any thickeners other than Clear Jel. Unfortunately, this product generally can’t be found in grocery stores, but it can be found online.
  • Flour. Some people believe they can make “cakes in a jar” or other foodstuffs that contain flour. This is strongly inadvisable. Home canned flour products , such as breads and doughs, are considered very prone to botulism. No one has yet been able to come up with a reliable recipe and canning direction that doesn’t produce botulism some of the time. Flour products are low-acid and “baking” them in a jar is not “canning”; it is not recommended.

The reasons behind the inadvisability of canning these foods are generally due to one of two things: either scientific research has demonstrated that home-canning of such foods is potentially hazardous, or the only way to can them is at such high pressures that the results are unpalatable. In other words, if it’s not possible to kill off botulism spores while producing a palatable product, then the food is placed on the “not recommended” list.

There will always be people who think the rules don’t apply to them, or believe they’re special enough to refute the science behind safe canning. This is the kind of sloppy canning techniques I continuously warn about. Remember, past performance (“Granny always did it!”) does not guarantee future results. Canning is a highly developed science, and to assume the rules don’t apply to you is asking for trouble. Be safe. – Patrice Lewis

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