Published in Moscow-Pullman Daily News (Aug 4, 2018)
Farmers Markets are filling up with a wide variety of delicious, fresh produce, which makes it the perfect time to think about preserving this produce for the dreary months ahead. Some of the most common questions we receive regard the canning of favorite recipes, or canning foods similar to those found in stores. However, the process of canning food is not so simple. Safe canning is dependent on several factors including the acidity of the food (pH), the amount of water available in a food to support growth of microorganisms (water activity), and the amount of time a food needs to be processed (heat penetration) to ensure the coldest spot in a can or jar of food has received adequate heat treatment to destroy microorganisms.
Commercially canned food has undergone rigorous testing to determine how the food will need to be processed to ensure it is safe. Unfortunately for the home canner, this means that only well-researched recipes and processes are safe for canning, and these recipes and processes must be followed exactly.
Botulism and Canned Food
Clostridium botulinum, the microorganism that produces the botulinum toxin, can grow and produce the toxin in canned food where the pH is above 4.6, and the water activity is above 0.86. This is most often an issue with home canned foods that contain vegetables and meats, and have not been properly processed. These low-acid foods must be processed using a pressure canner, unless a proper amount of acid has been added to ensure the pH is well below 4.6. Most fruit have a pH below 4.6, and can be processed in a water bath canner. However, some fruit such as Asian pears and white fleshed peaches can have a pH above 4.6.
Avoiding the Risk of Botulism
- Only use recipes which have been tested for safety. Contact your Extension office for more information.
- Use the appropriate canner for the recipe and follow all specified processing times and recipes exactly.
- Never fill hot food into the jar and let seal without processing. You must use the appropriate canner/canning method to process the food safely.
- Do not open, smell, touch, or eat any food from jars that are damaged, leaking, swollen, squirts liquid or foam when opened, or looks or smells bad. If you are ever unsure whether food is safe, throw it away.
- Boil home-processed low acid foods, like tomato sauces, meats, soups and vegetables, for 10 minutes in a saucepan before serving even if there is no sign of spoilage.
New to Canning?
Your local Extension office can provide you with safe recipes and processes to get you started. Most people prefer to start with water bath canning, as it tends to be a less complicated process.
Before you start you will need some supplies. Needed supplies include appropriate sized canning jars with 2-piece lids, a water bath canner or a large enough pot which will allow covering the jars completely with 2” of water (for water bath canning), a jar lifter, kitchen towels, and items specified in the recipe. A wide-mouth funnel and ladle will make filling jars easier. Many of these supplies can be found at your local hardware or grocery store. If you are pressure canning, you will need a pressure canner that is in good working condition. Canners with pressure gauges need to have the gauge checked for accuracy every year. You will want to make sure the gasket is flexible and not damaged, and the vent port is clean. Always fully read the manufacturer’s instructions for your canner before using.
Be sure to follow the directions in the recipe exactly, so your hard work will result in a delicious and safe product. You will need to know your elevation, as different elevations will require different processing times and pressure, if pressure canning.
Canning food is a great way to preserve the fresh produce available during summer. Your local Extension office can help you get started, so don’t be afraid to give them a call. Happy canning!