Preserving Food Safely is More Science Than Art

Food preservation has been part of just about every culture throughout history. Prior to today’s technology, ancient societies froze meat and seafood in icy climates or dried foods in tropical ones. Regardless of the century, all harvested or butchered food begins to spoil immediately. Food preservation methods are employed to slow down these spoilage processes and in some cases, stop them from taking place altogether. Let’s take a look at the different methods used for preserving food at home today.

Canning

Canning is the application of heat to food in containers and maintenance of a vacuum seal during storage. The goal is to have packaged moist food that can be stored for an extended time at room temperatures or without the need for refrigeration or freezing. The heating process kills microorganisms of concern for that particular food.  The ability to produce a vacuum seal on a jar is not sufficient alone to preserve food by canning; it takes much less heat to create a vacuum seal than it does to sterilize most foods.

Freezing

Freezing uses very cold temperatures to stop microbial activity during storage. In addition to the cold temperature affecting microbial activity, the water in foods is turned to ice and is unavailable for microorganisms to use in their metabolic activities. Freezing does not kill most microorganisms in foods but puts them into a state of suspended growth and activity.  When foods are thawed and warm up, most microorganisms will recover and resume their growth if other safe food handling practices are not followed.

Pickling

Pickling is the process of controlling many types of microbial activity through acidification. Pickling also significantly changes the taste and appearance of many foods.  Some of our most popular condiments and side dishes are the products of pickling. Besides sliced or whole pickled vegetables like okra, cucumbers, and beets, other foods in the pickled food category include relishes and salsas, chutneys, pepper sauces.  Often pickling is used to make interesting tasting foods and condiments for fresh use. Pickling can extend shelf life even for refrigerated products, but canning is recommended for those stored at room temperature. Canning can also further extend shelf life over refrigerated pickled products.  For pickled products to be safely canned, though, the actual recipe and proportions of acid and low-acid ingredients are important to the type of processing required. Not all pickles, relishes and salsas are the same when it comes to canning requirements.

Fermentation

Fermentation is another method of creating an acidic food situation to extend shelf life as well as create flavorful changes in foods. As with quick pickling, products of fermentation yield foods that do not exist naturally, such as sauerkraut from cabbage.  Fermentation is a longer process to complete preservation of foods, although the time required is very variable by type of food and desired taste of end product. Most fermentation relies on naturally occurring lactic acid bacteria to lower the pH of the food as a means of preservation.

Dehydration

Drying or dehydrating food removes enough water to preserve through lowered water activity. Bacteria may survive dehydrating of fresh food, but without enough water available during storage, they cannot multiply and cause problems.  Some will even die off under this condition. When the foods are rehydrated, microorganisms can recover and resume their growth if temperature controls and sanitary food handling practices are not used. The challenge in maintaining safe production of dried foods is to follow recommended drying temperatures and air flow, so foods do not stay too long in the temperature danger zone while drying down. 

Fruit preserves

Sugar concentration is another type of food preservation. Many microorganisms are inhibited in the presence of enough sugar. Traditional fruit-based jams, jellies and old-fashioned southern fruit preserves with thick sugar syrups are preserved in large part by their sugar concentration, although the acidity of fruits also helps. A good vacuum seal produced by canning also protects quality during storage. Freezing can also be used to extend storage times for versions of these kinds of products instead of canning.

Some risks presented today for people experimenting with all kinds of thickened fruit, vegetable or even bacon spreads is that they all get considered as a “jam.” The minimal processing that a high sugar concentration allows is not sufficient for all similar looking or tasting spreads.  Reduced sugar spreads or low-acid vegetable and bacon spreads can present real food safety risks if they are not preserved properly.

Why do we preserve food?

Home food preservation has been a major factor throughout history for achieving food security and prevent food waste. Over time, the goal expanded to include strategies to meet personal wellness and food safety goals as well as satisfy some needs for creativity in food preparation and maintaining family traditions. The reasons for preserving food vary greatly by culture, tradition, and individual. For some people, there is a large surplus of food that needs to be saved. For others, cultural preferences developed over time encourage them to preserve food. Still, others have chosen to preserve their food because they feel more confident about what is in the food; some react to notices of recalls and adulterated commercial foods by thinking they will preserve their own.

The growth in school and community gardens has also led to greater interest in food preservation in some communities. Those who want to foster support of local farmers and food distribution chains have caused some localized interests in community commercial kitchens and canneries also. Much more common beginning in the mid-20th century than they are now, community canneries were and are public facilities where individuals could bring their food to a small processing plant where it was processed for them. 

Nevertheless, with the currently increasing activity and interest, there is a large need for the general public to understand how to use methods of food preservation safely. If you are interested in learning more, explore the USDA’s Complete Guide to Home Canning. The Centers for Disease Control and Prevention (CDC) also has a dedicated webpage about safe home canning.

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This blog post was written by Elizabeth L. Andress, Ph.D.

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