I’ve heard conflicting information about the dangers of pressure canning food. How can I be sure the foods I’ve canned are safe to eat?
Learning to can foods can be intimidating, and it’s certainly important to do it properly. After all, sometimes there are no colors, odors or other handy indicators to betray potentially hazardous canned foods that could make you sick. But canning foods safely isn’t as difficult as you may have heard.
There are three main things that cause concern: equipment reliability, foodborne illness and altitude adjustments. Let’s get the first one out of the way, because it’s a snap.
Modern pressure canners are safe. You may have heard about pressure canners of yore exploding when pressurized. Rest assured, the canners available today are much more reliable than they used to be. According to the National Center for Home Food Preservation, home pressure canners were extensively redesigned beginning in the 1970s. Today they all have an automatic vent/ cover lock, a steam vent and a safety fuse. However, it’s still important to carefully follow guidelines that come with your pressure canner, both for safety and to be sure you’re canning at the correct temperature and pressure. (Keep reading.)
Avoiding foodborne illness is simple. The purpose of canning is to heat the food to a high enough temperature to arrest enzymatic activity and kill yeasts, molds and bacteria. Most of these nasties are knocked out by the acidity of foods or by heat. There are a few pathogens, however — most notably the one that can cause botulism poisoning — that thrive in low-acid foods and can survive temperatures up to 240 degrees Fahrenheit. That’s a potential problem because the temperature of water boiling in an open pan (or in this case, in a water bath-style canner) never reaches much above the boiling point of water — 212 degrees.
Pressure canners, on the other hand, can reach higher temperatures. Here’s why: These canners trap the steam that escapes from boiling water, thereby increasing the pressure on the liquid. When the pressure is increased, it takes more energy for the liquid molecules to escape the surface, so the temperature at which the water will boil becomes higher. The boiling point in a pressure canner is approximately 250 degrees.
In short, here is which canning method to use for which foods: 1. Use a water bath canner for acidic foods, such as pickles and many types of fruit. 2. Always use a pressure canner for low-acid foods, such as beans and meat, and for any recipes that combine low-acid with high-acid ingredients, such as salsa and soup.
Mountain-dwellers: Adjust for your altitude. Cooking at high altitudes can be weird. But the view is well worth it, so I bet you won’t mind making a few adjustments for canning. Here’s the rule: More altitude = more time or more pressure. Instructions on how to adjust for altitude will come with your canner. All of this safety talk should be helpful, but if this is your first introduction to canning, it isn’t enough information to get you started. To learn more, read “Home Canning Basics.” Be sure to follow all canning recipes carefully, use clean equipment and always discard any suspicious foods. If in doubt, throw it out!
—Tabitha Alterman, senior associate editor