There is a lot more to canning than merely getting the lid to seal on a jar of food. 

Some of the important considerations food scientists take into account when determining that a canning recipe is safe include the density and pH of the food, as well as the heat circulation in the jars and in the canner itself. Once these things are carefully determined in a lab, scientists inoculate test jars with microbes such as botulism spores, then monitor them during the canning process to ensure every particle of food reaches a temperature that will kill those microbes. This is done repeatedly, using different processing times and food from different sources, so scientists can ensure the results are consistent and not just an anomaly. Then, every so often, existing canning recipes are tested again, using new scientific knowledge and advances. When needed, the recipes are revised.

Unfortunately, none of this can be done accurately at home, which is why canners should always have an up-to-date copy of a Ball canning book or The National Center for Home Food Preservation website handy. The recipes from those sources are tested safe - meaning that if you follow them and use correct canning procedures, the food will be safe to eat and store in your pantry. 

Unfortunately, some people are distrustful of what they consider "government canning rules." (Even though Ball, a private company, plays a huge role in the safety of home canning by testing their own recipes.) This, along with misunderstandings about canning history and science, has led to an uptick in botulism cases from home-canned food. (Other types of food borne illnesses from home-canned food aren't tracked; however, they are much more common than botulism poisoning. Click here for more information on botulism and home canning.)

No one wants food poisoning - and especially not botulism poisoning, which can cause great injury or even death. The goal of home canning should always be to provide safe, healthy food for those we love. 

The good news is, we know which foods are tested safe to can and which are not. Below you'll find foods some people try to can at home, and why they are not actually safe for home canning. 

1. Dry beans.

Beans are perfectly safe to can (learn how here), but dry beans must always be rehydrated and partially pre-cooked before canning. This is because there hasn't been any testing done on canning dried beans without rehydrating and pre-cooking them first; therefore no one knows how long you'd have to process such beans in order to kill harmful microbes.

In addition, the older dry beans get, the more water they require to fully rehydrate. Therefore, if you can beans without rehydrating them first, you can easily end up with only partially rehydrated food. This means the water in the canner will not fully heat the beans in your jars. Proper, thorough heating is vital in order to kill any microorganisms that could make you sick.

Fully soaking dry beans, then giving them the partial pre-cook all tested safe recipes call for also means that some of the starch from the beans gets released before they go into jars. If you skip this step, the extra starch in each jar will make the food denser...which means the beans may not get heated thoroughly enough to kill off microbes. 

To preserve dry beans without rehydrating them, store them in a Mylar bag with an oxygen absorber kept inside a sealed bucket. Cooked beans may also be frozen.

2. Processed meat.

When I first started canning, I canned processed meats like ham and corned beef. I thought this was safe, since my Ball canning book gave instructions on canning pork and beef. But once meat is processed or cured, its density changes; no testing has been done to determine how to bring such meats to a temperature that will kill microbes that could make you sick. 

There are a few tested safe recipes from Ball and The National Center for Home Food Preservation that call for small amounts of ham or bacon. These recipes are safe because the creators understood the density issues with processed meat and tested the processing times accordingly. This does not mean that canning ham or bacon is, in general, safe.

Instead, store processed meats in the freezer or, if they aren't too fatty, run them through a freeze dryer. 

3. Certain Vegetables.

While vegetables in general are safe to pressure can (or to water bath can, if there is a tested safe pickling recipe for them), there are certain vegetables with no tested safe recipes for canning. This is due, in part, to the fact that they will turn to mush when canned in a way that kills off harmful microorganisms. These veggies include broccoli, Brussels sprouts, cabbage, cauliflower, eggplant, summer squash, olives, lettuce, and artichokes. 

Except for olives and whole Brussels sprouts, these vegetables may be preserved through dehydration. All but the olives may be freeze dried. (Dehydrated or freeze dried lettuce will crumble easily, so plan to use it as a powder.) All but lettuce and olives may also be frozen for storage.

4. Nuts.

Image courtesy of Wikimedia Commons and Silar.

Years ago, there were some recommended recipes for canning nuts, but due to more thorough testing, they are no longer recommended. We now know that salmonella can thrive under the conditions once suggested for home-canned nuts. 

To keep nuts for a longer period, freeze them. 

5. Ground poultry.

It's perfectly safe to can ground beef, so why not can ground poultry (such as chicken or turkey)? Well, there simply hasn't been any testing to see how long ground poultry - which has a different density than chunks or pieces of poultry - would need to be processed to kill off harmful microbes. An exception to this rule is the tested safe spaghetti sauce recipe in the USDA's So Easy to Preserve book. 

To preserve ground poultry, freeze dry or freeze it.

 6. Dairy and Fats.

Courtesy of Wikimedia Commons and Rainer Zensz.

While there are people who home can their homestead milk, butter, or lard, there are no tested safe ways to can dairy or fats of any type at home. This is largely because dairy becomes thick when canned, which makes it difficult to heat thoroughly - which is the only way to kill microbes that could make you sick. Plus, fats tend to go rancid, no matter how they are processed. 

Yes, commercial canneries offer some canned dairy and fats in grocery stores, but home canning uses completely different equipment than commercial canning.

The best way to preserve dairy is to either freeze it or freeze dry it. Or, if you want shelf-stable butter, you can turn it into ghee, which can sit in the pantry for at least 3 months. 

7. Eggs.

There are absolutely no tested safe ways to home can eggs. In fact, one of the more recent cases of botulism poisoning in the U.S. was from pickled eggs canned at home; the man who ate them only recovered after prolonged medical treatment. 

It's safe to make homemade pickled eggs, but they must include enough vinegar to acidify them (use a trusted recipe) and they must be stored in the refrigerator. 

Instead of canning eggs, consider storing unwashed eggs in the fridge for 6 months or more; or you may freeze or freeze dry them, or use mineral oil or lime to preserve them for a few months. Click here for details and more ideas on how to preserve eggs. 

8. Pasta, rice, and other grains.

It's fine to put pasta and grains in a canning jar and store them in the refrigerator, freezer, or pantry. You can even vacuum seal them. But they should never actually be canned. This includes putting pasta, rice, or grains in home-canned soups or using flour or cornstarch as a thickener in, say, home-canned pie filling. Canning makes grains go rancid, and during the canning process, they don't get heated thoroughly enough to kill off potentially harmful organisms. 

Pasta, rice, and other grains are best stored dry. For long-term storage, put them in a Mylar bag with an oxygen absorber, inside a sealed bucket. 

9. Pumpkin Puree.

Courtesy of Brownies for Dinner.

Although most people love the idea of canning their homegrown pumpkins into pumpkin puree that can be used to make pies, it's not safe to do so. In fact, in the 1970s it was found that there was simply too much variation in the viscosity of pumpkin puree to give safe guidelines for home canning it. 

That said, you may safely can pumpkin and winter squash chunks, which can be pureed after opening the jar. In addition, pumpkin puree may be frozen, dehydrated, or freeze dried. 

10. Previously canned food.

Some people love the idea of buying a big, oversized can of food from a restaurant supply or big box store, opening it, and then re-canning the contents into smaller jars. Unfortunately, this has never been tested safe. The initial processing of the food in a commercial cannery changes its density - and possibly its pH; this means you could be canning up food poisoning if you re-can the food. In addition, re-canning depletes the food of more nutrients and can turn the food to mush. 

Instead, plan to freeze or freeze dry excessive amounts of canned food. 

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