How does the canning process preserve food?

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By Melissa Hight, County Extension

So you want to try canning fresh vegetable and fruits this summer? You’ll be ahead of the game if you spend a little time understanding how canning preserves food for later use. The high percentage of water in most fresh foods makes them very perishable. They spoil or lose their quality for several reasons: 

1) Growth of undesirable microorganisms-bacteria, molds, and yeasts.

2) Activity of food enzymes (makes food continue to grow and age after harvest).

3) Reactions with oxygen.

4) Moisture loss.

Microorganisms live and multiply quickly on the surfaces of fresh food and on the inside of bruised, insect-damaged, and diseased food. Oxygen and enzymes are present throughout fresh food tissues. Proper canning practices include: carefully selecting and washing fresh food; peeling some fresh foods; hot packing many foods (heating them before placing in jars); adding acids (lemon juice or vinegar) to some foods; using only jars that are made for canning foods and self-sealing lids; and processing jars in a boiling-water or pressure canner for the correct period of time.

Using these correct practices removes oxygen; destroys enzymes; prevents the growth of undesirable bacteria, yeasts, and molds; and helps form a high vacuum in jars. Good vacuums form tight seals, keep liquid in and air and microorganisms out. 

Want to make sure you do it right? Come to one of the food preservation classes being offered by Cooperative Extension from 1-3 p.m. on May 25 and June 17. Both classes will feature the basics of canning and freezing with instructions on “how-to-do-it.”

Topics will include:

1) When to harvest produce.

2) Estimated yield of canned fruits and vegetables from fresh.

3) Cost of preserving and storing food. Is it worth your time and money?

4) Pros and cons of “doing it yourself.” Canning is not the time to be creative and invent recipes.

5) Why does food spoil and how you can prevent it; differences between canning, freezing, pickling and drying.

6) The importance of using the right equipment, including a pressure canner.

Participants will receive up-to-date instructions and learn reputable sources for recipes and instructions, including their own copy of the fifth edition of “So Easy to Preserve” from Georgia Cooperative Extension. The 375-page book contains 185 recipes with step-by-step instructions and the latest U.S. Department of Agriculture recommendations for safe food preservation. 

Testing of pressure canner dial gauges is free and will be available from 11:30 a.m.-1:30 p.m. Friday, May 6, and Friday, June 10. Simply bring the canner lid only with the gauge attached. It takes a few minutes for the peace-of-mind that comes from knowing the gauge is accurate. Only canners with dial gauges need to be monitored. It is not necessary to check canners with weighted gauges.

Cost for the food preservation class including “So Easy to Preserve” book and all other materials is $20. Pre-registration is required by May 10 for the May 25 class and May 27 for the June 17 class. Classes and pressure canner testing are both at the Cooperative Extension Center, 25 Referendum Drive, Building N, Government Complex in Bolivia. Class size is limited. Call 253-2610 for more information or to register. 

Source: “Complete Guide to Home Canning,” Agriculture Information Bulletin No. 539, USDA (Rev. 2009).