Why You Really Do Need To Leave Extra Room When Canning Food
We can thank Napoleon for kick-starting our love of canned foods. Yes, you read that right: Napoleon. France's most notorious emperor is responsible for encouraging his citizens to find a way to safely preserve food after witnessing his soldiers suffer from malnutrition. In response, chef Nicolas François Appert stepped up to the task and successfully created the first known method of canning in 1810 (via International Food Additives Council). Thanks to Appert, we can now open a jar of jam in the middle of winter or pop the lid off a can of dill pickles in the summer.
Today, most of us buy our canned goods from the store, but quite a few people still enjoy canning their own fruits and veggies; however, the process is a serious endeavor. Canning can be a surprisingly dangerous activity, so much so that the CDC has a part of their food safety page dedicated to proper canning techniques. It is important to use the right kind of equipment and methods to make sure everyone can enjoy the fruits of their labor without incident. One of these methods is making sure to leave extra room under the lid when canning food.
Yes, you must leave extra room when canning
It's easy to feel like you're wasting perfectly good space when you don't fill up your container to the very top, but when canning, it is important to strike a delicate balance. According to Utah State University, maintaining the space between the food and can lid is necessary to create the vacuum seal essential for preservation. If the food is too low or too high in the can, things could go wrong. It is especially important not to overfill the can and to leave sufficient space to create the vacuum seal; if not, the food could expand out of the can and allow bacteria to enter, which could cause those who consume it serious health problems (via CDC).
Another, more well-known, side effect of not properly sealing canned goods is the risk of explosion. If you've seen the classic 1942 film "Holiday Inn," you'll remember the scene where the protagonist, Jim, played by Bing Crosby, brings a friend some peach preserves. But, because of his bad canning job, they explode, and Jim and his friend are forced to duck for cover (via NY Times). This is a real canning problem. If there is not enough space left in the can, the lid will not seal and, yes, your canned goods might very well explode (via Shelf Life Advice)
Canning is a great way to preserve your foods and have a pantry full of delicious fruits and veggies all year long, but — for the sake of your health and safety — leave the recommended amount of space in the can. We don't want you to have explosive results.