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Food Preservation

June 2, 2022 - This page is under development.
NOTE: Research is ongoing - recommendations may change. Please refer to the National Center for Home Food Preservation (NCHFP) for the most current recommendations.

Excerpts from Historical Origins of Food Preservation by Brian A. Nummer, Ph.D., National Center for Home Food Preservation, May 2002.

The astonishing fact about food preservation is that it permeated every culture at nearly every moment in time. To survive ancient man had to harness nature. In frozen climates he froze seal meat on the ice. In tropical climates he dried foods in the sun.
Food by its nature begins to spoil the moment it is harvested. Food preservation enabled ancient man to make roots and live in one place and form a community. He no longer had to consume the kill or harvest immediately, but could preserve some for later use. Each culture preserved their local food sources using the same basic methods of food preservation
[historical origins of some food preservation methods]
In America more and more people live in cities and procure foods commercially. They have been removed from a rural self-sufficient way of life. Yet, for many, a garden is still a welcome site. And, annually there exists a bounty crop of vegetables and fruits. It is this cultural nature of preserved foods that survives today. Interests have shifted from preserve “because we have to”, to “preserve because we like to.”

Commercially Available Preserved Foods

Supermarkets are full of foods that have undergone one or more processes to delay spoilage. Refrigerators and freezers provide cold storage. Aisles of packaged goods are stocked with foods preserved by various methods to make them shelf-stable.

Excerpts from FSIS.USDA.gov  Shelf-Stable Food Safety

Foods that can be safely stored at room temperature, or "on the shelf," are called "shelf stable." These non-perishable products include jerky, country hams, canned and bottled foods, rice, pasta, flour, sugar, spices, oils, and foods processed in aseptic or retort packages and other products that do not require refrigeration until after opening. Not all canned goods are shelf stable. Some canned food, such as some canned ham and seafood, are not safe at room temperature. These will be labeled "Keep Refrigerated."

In order to be shelf stable, perishable food must be treated by heat and/or dried to destroy foodborne microorganisms that can cause illness or spoil food. Food can be packaged in sterile, airtight containers. All foods eventually spoil if not preserved.

Except for infant formula and some baby food, product dating — having a "use-by," "sell-by," or "best-if-used-by" date —
is not  required by Federal regulations. Dating is for quality, not safety. [Click to read more from FSIS.USDA about Food Product Dating.]

Will commercially canned goods last forever?  [NO!]

Commercial canning is done under tightly controlled conditions — careful sanitation and the necessary time and temperature under pressure, but there are still limits to how long it will preserve food. There are several factors that limit the shelf life of canned foods. First, cans can rust over time. Shipping accidents, where cans fall and dent or are crushed, also cause container problems.

Then there's can corrosion. In all foods, but especially in high-acid foods like canned tomatoes, natural chemicals in the food continually react with the container. Over several years, this can cause taste and texture changes, and eventually lower the nutritional value of the food.

High temperatures (over 100 °F) are harmful to canned goods too. The risk of spoilage jumps sharply as storage temperatures rise. In fact, canned goods designed for use in the tropics are specially manufactured.

Store canned foods and other shelf stable products in a cool, dry place. Never put them above or beside the stove, under the sink, in a damp garage or basement, or any place exposed to high or low temperature extremes. Temperatures below 85 °F are best. Check your pantry every few weeks and use canned goods you have had on hand for awhile. Don't purchase bulging, rusted, leaking, or deeply dented cans.

Preserving at Home

When we choose to preserve at home, we want the results of our efforts to be of good quality and safe to eat. The USDA and extension programs have published guidelines for safe home food preservation methods and recipes based on research and extensive testing. Watch UC Master Food Preserver Food Safety Training (a series of 11 videos that the University of California has made available to the home consumer) to understand the science behind food quality and safety. Video topics include food spoilage, microorganisms found in food the can be hazardous and environmental factors that affect the rate at which they multiply. Research is ongoing, so recommendations may change. Look for the most current recommendations at the National Center for Home Food Preservation (NCHFP).

Some food preservation methods are identified below, with a nutshell of the science behind making them safe while retaining quality. Two key factors are controlling pathogenic microorganism and deactivating enzyme that occur naturally in food. (In time, this page will have additional linked pages.

However you plan to preserve, start with food of good quality and adhere to food safety guidelines: clean - separate - cook - cool. Remember: If food doesn't look or smell right, it is better to throw it out than to risk your health.

Refrigeration and Freezing (cold storage)

Refrigeration does not kill bacteria, but storing food in a refrigerator set below 40 degrees Fahrenheit will slow the rate at which foodborne bacteria multiply. Inside the refrigerator's controlled conditions, food items can stay fresh and usable longer than at the ambient room temperature.

Many, but not all foods benefit from this cold storage. (See Food Safety page for information about storing leftovers.)

Freezing 

 

Drying

 

Pickling
Brining 
Fermenting

Fermentation

Canning

When canning home-preserved foods: 

  • Use scientifically-tested, up-to-date recipes such as those shown in this resource guide,  Home Food Preservation Recipes and Information
  • Follow directions carefully and do not change the measurements of fruit, vegetables, or acid. 
  • Adjust processing time for altitude.
  • Date home-preserved foods and store them no more than 12 months between 50-70 degrees Fahrenheit.  Avoid direct sunlight. 

Safe Methods of Canning Vegetables

Additional Resources

For more information, visit the NCHFP website and refer to some of the many extension publications and videos that are currently available.