How to safely can vegetables

As we approach the fruit and vegetable canning season, I thought it would be good for you to be reminded of some of the potential hazards of canning. Home grown green beans, peas, tomatoes, corn, and other vegetables can successfully be preserved by you, the home gardener. However, care must be taken to ensure the safety of these products. 

The actions of naturally occurring enzymes, bacteria, yeasts, and molds can all cause food spoilage. This week we look at bacteria since they are the most prevalent of these.

Bacteria are the major concern of canners, since there are so many different kinds of them. They also are able to survive under varying conditions of moisture, oxygen, temperature, and tolerances to acids and chemicals.

For example, some bacteria are known as aerobic, and function only in the presence of air.  Other bacteria are anaerobic, functioning only in the absence of air.  Most bacteria, however, are able to survive in either environment. 

Bacteria can also be grouped according to their heat requirements for growth.  Three basic groups exist:  cold-loving, growing at temperatures from 40 degrees to 68 degrees; intermediate, thriving at moderate temperatures from 86 degrees to 98 degrees; and heat-loving, which can grow in conditions up to 170 degrees.

The major objective in canning low-acid foods is to process them under pressure at a temperature sufficient to destroy spores of the bacterium Clostridium botulinum.  These low-acid foods have a pH of 4.6 or above and include fish, meat and most vegetables (beans, peas, okra, squash, etc.). High acid foods which do not require processing under pressure include tomatoes, peaches, pears, and the like.

Clostridium botulinum is an anaerobic bacterium which multiplies at intermediate temperatures.  It produces a deadly toxin, the ingestion of which causes a type of food poisoning called botulism.  It is so deadly, in fact, that a spoonful of the toxin might kill a million people.  Botulism disease is greater than 60 percent fatal to man.

The organism causing botulism comes from the word “botulus” – meaning “sausage.”  The first case reported was in Germany in 1735, and was caused from the consumption of infected sausage.

From 1900 to 1941, there were found to be more than 1000 cases reported in the U.S., nearly 700 of which were fatal.  A few deaths a year still occur, arising mostly from home canned vegetables and meat.  Death is generally due to respiratory failure, and comes three to six days following ingestion.  Non-fatal cases recover very slowly.

Clostridium botulinum is soil-borne, and can be found in both fruits and vegetables.  Fruits, however, will not permit bacterial growth or spore formation due to their acid nature.

Vegetables, which are low-acid, will permit bacterial growth and production of reproductive organs called spores which, when they germinate, produce the toxin which causes botulism. (The bacterium itself is not harmful when ingested).  Boiling vegetables will kill the vegetative cells but will not destroy any spores present.  

Thus vegetables should be processed under very high temperatures and pressure for a specific time to destroy Clostridium botulinum spores.  It is also recommended that anytime you open a can of processed vegetables or meat that you boil the contents for 15 minutes before consumption. This will destroy any toxin present.  

You home canners be careful! Stay informed as to recommended canning procedures, cooking temperatures, blanching and washing, etc. The guidelines mentioned in this article are only general rules. Your county extension office is always very helpful with this, as is the staff at the Argene Claxton Canning Plant located on Houston Lake Road at the site of the old Houston County bus shop. I’m sure they would welcome a call or visit. 

Tim Lewis is a Georgia Green Industry Association Certified Plant Professional, gardening writer, former Perry High School horticulture instructor, and former horticulturalist at Henderson Village and Houston Springs. He and his wife, Susan, own and operate Lewis Farms Nursery located on Hwy 26 two miles east of Elko, where he was born and raised. He can be reached at (478)954-1507 and timlewis1@windstream.net.