Canned foods are a convenient way of eating fresh foods at a later date but errors in the canning process can be fatal.
Food poisoning is one of the deadly side effects of eating canned foods that have been exposed to the bacterium Clostridium botulinum. This bacteria, commonly just referred to as botulism can exist as a spore or vegetative cell. In spore form, which resembles plant seed, the bacteria can survive for many years in water and soil. If the conditions become ideal, the spores grow vegetative cells which are fast multiplying, producing a deadly toxin in the process. All this takes place within four days if the environment has less than 2% oxygen, there is moisture on low acid food and the temperature is between 40°F and 120°F. The potent spores of Botulinum are present on fresh food surfaces but they will only grow if there is no air.
Even with the high levels of sterilization involved in canning, it is impossible to completely remove molds, yeast, and bacteria from food surfaces. Some of the processes that help to reduce their numbers are washing, peeling and blanching.
What Causes Botulism?
The spores of Botulism are heat resistant even if boiled in water and will thrive in a moist environment without oxygen. One of the byproducts of botulism reproduction is a poison that is capable of killing 100,000 people with a single teaspoon. If home canning is not done properly, the perfect breeding environment for the growth of botulism is created. The problem with botulism infestation is that the food still smells and looks fresh.
Identifying spoilt canned food
Growing up, most people were taught to be aware of food packaging that appeared to bulge; this is true for canning too. As a matter of fact, bulging of a metal can is a red flag and a cause to be suspicious about the safety of the food inside. Here are some guidelines to identify defects in metal and glass canning containers;
- Metal cans – follow the double seam from top to bottom and make sure there is no obvious opening underneath it. red flags include any sort of puncture on the surface of the can, a portion of the seam that appears unwelded, a fracture of the double seam and bulging on either end.
- Glass jars – red flags include a pop top that does not produce the popping sound when being opened indicates that the protective vacuum has been compromised, damage to the seal and cracks in the glass jar body.
Getting rid of spoiled canned food
You may be tempted to taste food in a defective container just because it does not look spoilt but do not because that is poison.
- If the spoilt food is acidic in nature, discard it at a location where pets and human beings will not accidentally consume it.
- Treat all cans with spoilt food as though they had the deadly botulinum and discard either by placing in a heavy garbage bag to throw in the trash or bury in a landfill.
- If the suspected spoilt food is unsealed, open or leaking from its glass jar container, detoxify by placing the container on their side in a pot of water which must then be brought to a boil and heated for 30 minutes. All the utensils used should then be thoroughly sanitized.
How dangerous can the Botulinum toxin be?
In all foods that are low in acids, all non-fruit foods, the botulinum toxin continues to grow long after the canning process is complete if it was poorly done. Improper handling of food is a fertile breeding ground for listeria, salmonella, and E.Coli that cause serious illness and death.
To bring the picture into perspective, if you dip your finger in food contaminated with botulinum and then licked it, the poison you swallow is enough to kill you.
The bottom line is that canning should be left to the experts because breaking a simple rule of the process is risky business.
Controlling Botulism in canning
- There are two main methods when canning food; use a pressure canner or boiling water canner. The choice will depend on the acidity of food in question but each controls the botulism bacteria if done correctly. Acidity is a natural botulism control and you do not have to do anything to enhance it in most fruits. You may, however, add acid from lemon juice, vinegar or citric acid to pickled foods to control the botulism bacteria.
- Low acid foods, on the other hand, include meats and fresh vegetables. The cans should contain low acid food and acid food before it is sealed. Lemon juice, citric acid, and vinegar are often added to food to make it acidic.
- Food like tomatoes and figs are considered acidic foods but their pH is above 4.6. When they are being canned, their pH should be lowered with citric acid or lemon juice before processing in a canner.
- The spores of the botulism bacteria are quite difficult to destroy but as the temperature of the canner goes up, they are unlikely to survive. Low acid foods must, therefore, be sterilized at between 240°F to 250°F which can be obtained if the pressure canner is operating at 10-15 PSIG. The time required to kill bacteria can be as low as 20 minutes or as high as an hour and 40 minutes but the exact duration depends on the food type being canned, altitude and size of jars.
- Canning errors as a result of errors in temperature can be controlled by following the strict guidelines for canning pressures specified for each region and altitude. Air that is accidentally trapped in a can will lower the temperature of the process and the result is under-processing. Such errors are most likely to be encountered when processing raw foods for canning. The dial gauge canners used are not designed to vent out air and so they do not. To be safe, vent all types of pressure canners for at least 10 minutes before pressurization.