Science behind food preservation methods

Why have food preservation times, pressures and approved methods changed?

Various mason jars of canned fruit.

Your family has preserved food for years, so why would you need to attend a food preservation class? While many food preservation methods that have been used in the past are still used today, some have been updated to follow the latest science. Understanding the current methods for preserving food at home is critical to ensure a safe product for you and your family.

When preserving food, first you need to decide what you want to preserve and then find a research-based recipe, which will tell you what preserving method to use. 

Dehydrating is one of the oldest forms of food preservation. This method removes moisture from food. Removing moisture from the product reduces the ability of bacterial growth by taking away the element it needs to grow. In some areas of the world, it is difficult to keep food safe as a dehydrated product due to humidity. If humidity is an issue, it may be best to dehydrate the food and then freeze it to keep bacteria from growing. Keeping dehydrated food in airtight containers is beneficial to maintaining dehydration levels required to keep food safe.

Water bath canning is used when putting high-acid foods, such as fruit jams/jellies and tomatoes, in a jar and then processing them in a canner. The latest food preservation research has determined it is necessary to add acid to tomatoes when canning them. Because of science, the length of time produce is in the water bath canner has also increased to ensure that the heat has reached the center of the jar to kill any bacteria or enzymes in the product.

Atmospheric steam canning has been used for a while, but it was not an approved preservation method by the United States Department of Agriculture (USDA) until recently, when research determined it was a safe method of preserving high acid foods, so long as specific recommendations are followed. It is important to note that when using the atmospheric steam canning method, the processing time should never go over 45 minutes, because the amount of water used in the bottom of the canner has a potential to boil dry after 45 minutes. Read and follow the directions carefully before using the atmospheric steam canner.

Pressure canning is another preservation process that requires processing product in a jar. Always can low-acid foods, like vegetables and meats, in a pressure canner. Research is continually being done to determine the safety of the processing times and the amount of pressure used when canning with a pressure canner.

Pickling is a method of preservation that has a high concentration of acid. Pickled products are saturated with acid to help with the preservation ph of the food. Heat treating these products, using a water bath or steam canning method is still needed to kill any chance of potential bacterial growth that may remain in the jar.

Freezing food is quick, easy and probably the most affordable method of food preservation. Many foods can be frozen without disruption of flavor, color and nutritional value. Freezing slows growth of enzymes but does not eliminate them. When foods are removed from the freezer microorganisms begin to grow once they reach a thawed state, so it is important to thaw all foods in refrigeration to keep them safe.

When it comes to home food preservation, recommendations and methods have changed through the years. To keep yourself and your family safe when practicing home preservation, be sure to use research-based recipes. Michigan State University Extension offers Home Food Preservation classes to increase your knowledge and confidence in everything from pickling to dehydrating techniques.

For more research-based information on methods of food preservation refer to USDA National Food Preservation, So Easy to Preserve, Michigan Fresh Fact Sheets or the Ball Blue Book 37th edition.


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