The Biggest Mistakes People Make When Canning Food

From cost savings to making healthier food choices by staying clear of BPAs or preservative-laden foods, there are several reasons why an individual would forgo store-bought canned goods and venture out to make their own. Although the process of canning food items was first introduced in the 1800s as a necessary practice for stocking the cellar with vegetables and fruits for the upcoming winter, many continue the tradition in the current day. The phenomenon has now become a source of pride for indulging hobbyists, a way to connect to the practices of generations past.

When diving into the true bare bones of the process, canning is primarily a method of removing the oxygen from a food, which is what microorganisms require to thrive. These microorganisms are what eventually lead to mold, decay, and yeast buildup. Essentially, they are the culprit to blame when your delicious block of cheese starts growing fuzzy green patches. Each type of canning requires a slightly different process, though, so whether you're using boiling water, a pressure canner, or an atmospheric steam canner, there will be a learning curve in the process. Whatever your reason for taking the first step on the canning journey, learning the common pitfalls before diving in will help ensure you are well-prepared for this new chapter.

If a recipe calls for lemon juice and a big bag of lemons is sitting in your crisper, you may think using them is a no-brainer, especially if a bottle of lemon juice isn't readily available. Or perhaps you simply prefer the fresh stuff (and all its vitamin C), so you figure you'll swap the bottle out for hand-squeezed juice. However alluring the benefits of fresh lemon juice are, it's not a good idea to replace the bottled variety in this case, even if you're super excited to try out that new hack for getting more juice out of a lemon.

Using fresh lemons when a recipe calls for lemon juice could alter the concentration of acid in the recipe. Bottled lemon juice has a far more consistent acidity than homemade juice, which the recipe is relying on to produce a properly preserved product. Changing the acidity in the jar could be dangerous, as this also affects the carefully crafted pH level and could then result in bacteria growing.  Remember, the goal here is to create an environment where bacteria cannot grow, so that the food remains preserved. Forgoing bottled lemon juice for fresh-squeezed could be the difference between a successful canned food and a bacteria-ridden one. 

Even if you're faced with a slight excess of product, cramming a jar to the top is a mistake you'll want to avoid. Recipes actually strive to avoid this by providing a measurement of something called "headspace". Headspace refers to the amount of space between the top of the food and the bottom of the lid. If the headspace is off due to over- or underfilling jars, that ever-important vacuum seal can be affected, which could lead to unsafe food or food discoloration. Discolored food isn't necessarily unsafe to eat, though it might be off-putting to eat brown vegetables that are normally green.

The process of measuring headspace is an exact science. It's far less willy-nilly than measuring a pinch of salt or a sprinkle of sugar in a recipe, though there seem to be countless methods for measuring it. Some common methods involve sticking a household ruler into the jar, or simply looking at markings on the side of the jar, like the bottom ring of the rim, which often marks an inch of headspace. For those looking for fancier methods, you can buy measuring tools for canning (the bonus here is that many are plastic and can also be used for bubbling jars).

Typically, the recipe direction to remove air bubbles from your canning jars will be phrased as "bubble your jars." This is usually done before placing the cap on a jar and moving it to your canning device of choice. The process is far easier to do than it might sound; a utensil is taken and slowly swirled around the edge of the jar, jostling the contents and thus loosening any air bubbles that might be trapped inside. It is recommended to use wood or rubber, as using metal could lead to a secondary mistake: scratching the glass of the jar and lowering its durability.

There are several reasons why failing to remember this step is a mistake, however simple it may seem. Trapped air within the jar could bubble up to the top during the canning process and tamper with the vacuum seal (potentially becoming stuck underneath and not allowing it to seal properly). If trapped within, the bubbles could also add to the headspace that was previously allotted for, tampering with the air-tight seal in a whole different fashion. With the vacuum seal being the main thing preserving the food, it's easy to see why the bubbling step shouldn't be skipped.

If the canning process eliminates harmful bacteria, this might spring to mind the assumption that all foods can be canned. After all, microorganisms like bacteria and oxidation are some of the main culprits as to why people are constantly checking how quickly their food will spoil, which the canning process essentially neutralizes. However, not all foods can withstand the canning process effectively and remain safe for consumption. If unsafe foods are canned, this can lead to a very serious illness called botulism. It is associated with many unpleasant side effects, including possible paralysis. 

Some foods do not properly heat through during the canning process, such as dense purees. This is easy to fix by simply changing the form of the food; for example, instead of canning mashed potatoes, which are too thick, can the whole small potatoes, which will be preserved effectively. Other foods are simply chemically incompatible with the process, such as bread and cakes. These foods have a very low acid level, which means if canned and eaten, they could cause illness. On the other hand, broccoli and eggplant are low-acid foods that, if canned, would not promote the growth of harmful bacteria, but the pressurizing process involved would turn them into mush. For these reasons, before canning a food item, doing the research on whether it can be canned safely is a checkpoint you won't want to forget.

A canning recipe is more than just a list of suggestions. It is a tried and true scientific process, which has been formulated to ensure the food is canned effectively. Recipes from reputable sources have been tested and practiced, producing a result that is safe for consumption. Creativity is great when crafting new drinks with rum or trying out a new method of cooking steak. But if you start getting creative and going off-script from your canning recipe, this could alter the ever-important acidity of the recipe and lead to serious health concerns later, as harmful bacteria grow.

While going completely off-script is a serious no-no, there are some minor adjustments that canners can make that won't mess with the acidity of the food item. One example of this is the level of salt in a recipe. This is only added for flavor in vegetables, meats, and soups, which means adding in a dash more or less won't cause any issues. The only exceptions for this are in canned pickles and sauerkraut, where the salt is added into the recipe as more than just flavoring. Another example is the sugar levels when canning fruit. Typically, a homemade syrup is created for this process by boiling sugar and water. The sugar level in these syrups can be adjusted safely without affecting the food's safety. Word to the wise on this, though, the sugar is what helps canned fruit remain firm and keep its coloring, so if these two things can't be compromised, it may not be something you want to tamper with.

Recipes will often specify a jar size, and this jar size may not match what you currently have on hand. Swapping out the size for a larger jar might seem like a truly innocent way to use up those 64-ounce jars that have been lying around, a resourceful decision even. But here lies a trap that many first-time canners may fall into. Canners should always strive to follow the jar size specified in the recipe, with one little caveat. 

The reason that larger jars cannot be swapped out is that the processing time required to allow the heat to properly reach the center of the food will be much longer than noted in the recipe. If the larger jar has not been properly tested, with a specific processing time noted, canners could be risking their health by using larger jars, as the food may not process properly. Here's the good news: If smaller jars are gathering dust in the closet, these can actually be swapped out in the recipe without compromising the final product. However, even though the jar is smaller, it will still need to be processed for the same amount of time that the original size would have required.

The air changes depending on what altitude a person is standing at, a fact that can slip the minds of even those who live at high altitudes. The higher the altitude, the less oxygen and atmospheric pressure are observed, and for this reason, water boils at lower temperatures in areas of high altitude. This causes cooking to take a bit more time in high altitude areas than for those cooking at sea level. 

With this in mind, the processing times for canning will need to be adjusted accordingly to ensure food remains safe. If a boiling water canner is used for processing, the time spent in the boiling water will need to be increased. If a pressure canner is used, the weighted and dial gauges are going to need adjusting. This might sound a bit intimidating, but don't worry – there are several charts available that can help those newer to both canning and high-altitude cooking navigate this change properly.

In this day and age, when consumers are becoming more environmentally friendly, reusing the lids of canning jars seems reasonable. Buying new lids for the next canning batch might seem like a waste of products, but this is actually a safety-conscious decision that can save a canner from the resulting disappointment of spoiled food products. This is because these jar lids have a gasket function, which is triggered when used. This gasket allows air to leave the jar during the hot processing period of canning, then provides an airtight seal around the lip of the jar when it has cooled. 

As nifty as this function is, the downside is that it's a one-time deal. Reusing the same lid twice can cause this gasket to malfunction, potentially allowing bacteria to get into the precious cargo inside the jar. For this same reason, pay attention to any dented or misshapen lids, as this could also affect the quality of the vacuum seal. For those who prefer not to throw lids away, never fear. There are several other ways in which these lids can be reused, even within the kitchen; for example, Ree Drummond uses them to bake mini pies.

Oven canning was trendy in the early 1900s and was often spoken about as an easy alternative to the other options. There was less risk of being burned by steam, and it didn't elevate the kitchen temperature as much as other canning processes did. By 1917, the United States Department of Agriculture (USDA) had announced the method was only safe for low-acid foods. However, by 1940, after a two-year study on oven canning, it was announced that there were too many variables for the process to be considered safe at all. 

There are several reasons why this practice is not recommended, the first being that the precise temperature inside an oven is going to slightly vary depending on factors like how well the heat is circulated and maintained. Often jars are not constructed for oven usage, and can shatter or explode if used in the oven. The oven's dry heat also takes a long time to heat jars all the way through, which could cause harmful bacteria to remain in the food. And above all, sure, there are recipes to follow from back in oven-canning glory days, but there are no scientifically tested oven-canning recipes, and so the process remains unsafe. Taking all of this into consideration, it might be hard to believe that there are still individuals out there who continue to practice this method regardless of the safety concerns. But oftentimes the practice has been passed down through generations of family members, and traditions can be hard to break. 

When an item like a glass jar is heated or chilled, it expands or contracts. When a jar expands or contracts due to a rapid temperature change, this can cause it to break or crack in response. This reaction is called thermal shock, and is a very common reason for canning jars to bite the dust during processing. 

Essentially, the rule here is to never combine a hot or cold jar with something of the opposite temperature. For example, always be sure to warm the jars before dropping them into the water bath if water bath canning. Or if pressure canning, warm up the canner before dropping the hot jars inside so they aren't met with a cool canner. Once removed from the canner, be sure to keep the hot jars off the cool counter, as this could also lead to cracking or breaking. Something as simple as a cool breeze hitting the hot glass may cause breakage to occur, which is why being aware and cautious of thermal shock hazards during the process will help make canning a much smoother procedure.

After reading about all the pitfalls of the canning process, you might feel prepared enough to jump headfirst into canning. But before you do so, take a pause and consider some safety preparations, as canning comes with risks that can be greatly mitigated if the proper tools are handy in the kitchen. One example of a helpful tool, according to the Reddit community, is using a glove or oven mitt to avoid burning your hand. 

During the canning process, processes like sterilizing and prewarming jars and lids involve submerging them in boiling water, and then, of course, resubmerging if using the water bath canning process. During pressure canning and atmospheric steam canning, the jars will still get burning hot due to the steam, so using either gloves or mitts would be useful here as well. Heat-resistant nitrile gloves are recommended by one Reddit user, as traditional oven mitts can feel a bit clumsy without the full use of your fingers that the gloves would offer. Alternatively, a jar lifter can put some distance between your precious fingers and the hot jars. For the lids specifically, there is also a tool called a canning wand or magnetic lid wand, which helps to fish the lids out of their hot water bath easily, without worrying about burns.