The Methods Not to Use When Canning Foods

By Mary Loftis, Extension Associate

Avoid Unsafe Canning Methods

It’s the time of year many people spend a lot of time, effort and money on preserving foods at home for future use. I recently canned a box of peaches, but I always consult my USDA approved methods booklet (and/or website) for the correct methods and processing times. I hope you do too! I

f you need to look it up you can go to the Nebraska Extension website http://food.unl.edu/canning or google USDA Home Canning which will lead you to the National Center for Home Food Preservation to get to the most current recommendations.

Some Canning Methods are Unsafe

Have you heard that some methods of canning are not recommended, but you don’t understand why? Let’s look at a couple methods that are NOT safe and why.

This information comes from Penn State Extension and is available on the Nebraska Extension website http://food.unl.edu/canning

Open Kettle Canning – Unsafe

Since the late 1980’s we have been teaching that open kettle canning is no longer safe. Open kettle canning involves heating the food to boiling, pouring it into the jars, applying lids, and allowing the heat of the jar to cause the lid to seal. Many years ago, it was commonly used for pickles, jams and jellies, and sometimes used for tomatoes and applesauce.

The reason open kettle canning is no longer recommended is that the food is not heated adequately to destroy the spoilage organisms, molds and yeasts that can enter the jar while you are filling the jar, and it does not produce a strong seal on the jar. This method is not safe! Processing jars in a boiling water bath or in a pressure canner drives air out of the jar and produces a strong vacuum seal.

Open kettle canning is not safe! It is especially dangerous when used for canning tomatoes or tomato products where the acid level may be low enough to allow bacterial growth. Never open kettle can low acid foods (meats, vegetables, soups) that should be pressure canned.

Just because a lid “pops,” it doesn’t mean the contents inside the jar are safe. The time saved with open kettle canning is not worth the risk of food spoilage or illness.

Oven Canning – Unsafe

Occasionally people ask about processing jars in the oven. They claim a friend or neighbor promotes it as a simple method of canning. What they fail to understand is that oven heat is not the same as heat from a boiling water bath or from steam in a pressure canner.

First of all, placing jars in the dry heat of the oven may cause the glass to crack and shatter causing injury to you. The Jarden Company that manufacturers most canning jars in this country states emphatically that it is not safe to heat glass jars in the dry heat of an oven. Jars are not designed to withstand oven temperatures and can break or even explode causing injury from broken glass.

Secondly, dry heat is not comparable to the moist heat of a boiling water bath. Processing in an oven will not heat the contents in the coldest part of the jar in the same way as boiling water.

Thirdly, oven heat will not increase the temperature inside the jar above boiling to be adequate to destroy botulism spores in low acid foods. Only in the enclosed conditions of a sealed pressure canner will you be able to increase the internal temperature to 240°F. Oven canning is not recommended!

Use Up-to-Date Canning Recommendations

The USDA Complete Guide to Home Canning, 2015 is the most recent update of the canning guide. Two of the revised recommendations that are most frequently noted involve the waiting time recommendations below. These new waiting time recommendations were added to improve lid performance and reduce sealing failures.

Water Bath Wait Time: 5 Minutes

Water bath canning directions were updated, advising consumers to “Wait 5 minutes before removing jars” to be consistent with a major canning lid manufacturer’s advice based on their research on lid functioning and seal formation. (When using a boiling water canner: “After jars have been processed in boiling water for the recommended time, turn off the heat and remove the canner lid. Wait 5 minutes before removing jars from the boiling water bath canner.”)

Pressure Canner Wait Time: 10 Minutes

Pressure canning directions were also updated advising consumers “After processing, remove canner from heat and allow canner to cool naturally to 0 pounds pressure. Wait 2 minutes and remove weighted gauge or pressure regulator. Wait 10 more minutes before removing lid—this will reduce siphoning (loss of liquid from the jar).”

Check Your Pressure Canner Gauge

If you are using a pressure canner you need to make sure your pressure canner gauge is accurate. Nebraska Extension in Burt County (in the Burt County Courthouse in Tekamah) has a pressure canner gauge tester if you want to make sure you are accurate. Call our office at 402-374-2929 to make sure someone is available to test it for you. If you have a weighted gauge canner you should have no problem with the accuracy, just be sure your rubber seals on the lid are pliable and not hard and cracked.

Know Your Altitude

When canning foods, it is important to know your local altitude. Your altitude determines the amount of pressure (pressure canner) or time (boiling-water canner) for your food. In Nebraska, the altitude ranges in elevation from about 1,000 feet to 5,000 feet above sea level so we need to add on the additional recommended time as most areas are above the 1,000 ft. level.

Happy and Safe Canning!