Friday Food Preservation: Water Bath Canning Explained

By Cassidy Hobbs Hall
Area Agent, Family and Consumer Sciences
Johnston County Cooperative Extension

This is the 4th in a series of 6 Food Preservation articles that will publish each Friday

When I first began my career with Extension, I received extensive training in food safety and preservation from a team of food safety professionals at N.C. State University. Once people learn that N.C. Cooperative Extension offers canning classes, they love to tell me how they learned to can, which typically involves very risky practices that make me cringe. I’ve heard everything from “I just put a lid on it and it seals” or “I add water and boil green beans in a jar” to “I put the lid on and stuff it in a cooler with towels.” Safe and quality products require strict adherence to tested recipes which involve pH, processing time based on a variety of factors, using the correct canner method, and ensuring a proper seal achieved by oxygen compressed from the jars. The correct combination of these components ensure food does not spoil and the risk of contracting foodborne illness is nearly eliminated.

Although recipes may have floated through your family for years, that does not ensure you are creating a safe product today. If you were diagnosed with a serious condition, would you want to follow medical recommendations from 1920 or would you want the most updated, data-driven information? Canning is no different. Following a tested recipe means following procedures recommended based on research. (Yes, teams of researchers have actually been tracking heat penetration, pH of foods, and the amount of time it takes to drive oxygen from jars based on the size of food, variety of food, and more.) You can find tested recipes in Georgia Extension’s So Easy to Preserve, the 100th edition of the Ball Blue Book, and the National Center for Home Food Preservation website. If you’re new to canning, it is important to note that there are two types of canners: water bath canners and pressure canners. You would use a water bath canner for foods with a pH of 4.6 or lower and you’d use a pressure canner for foods with a pH greater than 4.6.

Jams, jellies, fermented and pickled foods, as well as acidified foods, such as tomatoes with the addition of vinegar or lemon juice, may be processed using a water bath canner. These foods either contain enough acid naturally or have acid added to them. The acid in these foods is coupled with heat processing to prohibit growth of microorganisms that can result in food spoilage. Foods are packed into warm jars with a lid secured and loaded into a water bath canner. A water bath canner looks like a large pot with a lid. Water bath canners have a rack, which ultimately looks like a large trivet, in the bottom of the pot to ensure water and heat properly circulates around the jars. Once water reaches boiling, you begin your processing time. This processing time works to drive oxygen out of the jars to make a shelf-stable product. Once the jars have processed for the necessary length of time, they are removed and placed on a towel to cool. This cooling process should not be rushed. Oxygen is driven out of the jars during processing, but the cooling process is what actually seals the jars. It is important to note that new jar lids should not be boiled prior to use. Boiling these one-time use lids ruins the sealing compound.

Water bath canning is very easy to do which is why consumers enjoy this process- sometimes to a fault. As I mentioned previously, water bath canning requires bringing water to a boil to begin processing. Water boils at 212 degrees (F). This degree of heat works with the food’s pH to prohibit the growth of microorganisms responsible for food spoilage. Note, this is not the same as microorganisms responsible for foodborne illness, specifically Clostridium botulinum.

Remember how I mentioned that processing drives oxygen out of the jar to make a shelf-stable product? This oxygen-free environment is the perfect condition for Clostridium botulinum to create heat-stable toxins resulting in an illness known as botulism. Botulism first mimics a stroke by attacking the central nervous system resulting in drooling, facial paralysis, and in severe cases, paralyze the diaphragm, resulting in fatality. Vegetables and meats should be pressure canned because they do not contain enough acid to prohibit the growth of C. botulinum. Low-acid foods must be pressure canned to achieve heat penetration of 240 degrees (f).

I’ll save pressure canning information for next Friday’s edition of Food Preservation Friday. Home-canning is a great way to preserve locally grown foods. If you are interested in home food preservation, be sure to check out the upcoming series offered by N.C. Cooperative Extension- Johnston County Center. Due to COVID-19, this year’s food preservation series will be held virtually. Participants must register and must attend live. Workshops will not be recorded. More information can be found here.

May 15th Article: Gearing Up to Preserve Local Foods
May 22nd Article: Dos and Don’ts of Freezing Produce
May 29th Article: Handling & Freezing Meats, Eggs, & Dairy