What is Clostridium botulinum?
Clostridium botulinum is a bacteria, which when found in its dormant state, is a rod-shaped spore. These spores are present on most fresh food surfaces and can survive for many years in soil and water harmlessly. When ideal conditions for growth exist, the spores germinate into actively growing cells, which are initialy harmless. As these cells rapidly multiply, they become overpopulated and begin to die. As these cells die, they can produce a deadly neurotoxin within three to four days. This neurotoxin can be absorbed into the blood stream through the respiratory mucous membranes as well as through the wall of the stomach and intestine. Very small amounts of the neurotoxin can cause an often fatal disease called botulism. This toxin is the most deadly known to food scientists: about one microgram is lethal to humans.
Conditions for Growth
The conditions that must be present for the germination and growth of C. botulinum are:
- moist food (water activity > or = 0.940)
- low-acid food
- sugar content lower than 50%.
- a temperature between 40 deg and 120 deg F
- less than 2 percent oxygen (jar of canned food)
Preventing Botulism
The acidity level is a primary factor for the germination and growth of C. botulinum spores. A pH level of 4.6 or lower is needed to inhibit growth. A temperture below 38 deg F and heating above 250 deg F will also inhibit the growth.
In order to kill the growing cells and inactivate the spores formed by C. botulinum they must be heated under high pressure to 250 deg F for at least twenty minutes. The pH of a food also has an influence on the amount of heat necessary to kill the spores. The higher the pH (lower the acid level), the greater the amount of heat needed to kill the spores.
You can’t see, smell, or taste botulism poison. C. botulinum toxin can be present in the absence of visual spoilage, such as bulging cans or lids.
Oven Canning
With oven canning the temperature will vary according to accuracy of the oven regulator and how heat circulates. The temperature will also vary considerably between the “on” and “off” cycles, so heating is uneven. There are no safe and reliable processing times or temperature settings established for home canning in an oven.
For a product in an open jar the ingredients of the product determines the maximum temperature it can reach, no matter how high the oven is set. Once all the moisture is gone in the product, it will slowly go up to oven temperature. For example: If the product was water, it would maintain a temperature of 212 deg F at sea level until all moisture is gone. If the product was water with a large amount of salt or sugar mixed in, it would maintain a temperature of approximately 214 deg F at sea level until all moisture is gone. Each additional ingredient, and its quantity, will affect the temperature in a positive or negative way, which makes it almost impossible to know the maximum temperature reached.
Canning Breads and Cakes
Most of the botulism events that are reported annually in the United States are associated with home-canned foods that have not been safely processed. In recent years around 30 cases per year have been reported.
Studies at Kansas State University and Utah State University did microbial experiments on canned breads. They intentionally added spores to the batter and then baked the three samples at 350, 375 and 400 deg F. The temperatures at the centers of the breads reached 223, 225 and 226 deg F. Also, the water activity (aw) ranged from 0.93 to 0.95 and pH from 7.6 to 7.9. Immediately after baking, the active form of the bacteria could not be detected, but many of the spores survived. The samples were then stored for 90 days at 95 deg F. After 90 days the samples were tested and showed microbial growth.
Since you can’t rely on heat to kill C. botulinum spores in the oven, your only other option is to control the pH, sugar or water activity in the recipe, so that when the product is vacuum sealed it will inhibit the growth of C. botulinum.
Utah State University did do research to see if it was possible to either raise or lower the acid level enough to control C. botulinum or add enough sugar to control water activity while still having a palatable bread. They were unable to formulate a safe product.
Botulism found in Canned Cake: Minnesota Department of Health
http://www.health.state.mn.us/divs/idepc/newsletters/bugbytes/0701bb.html
Canned Jams and Jellies
Home-canned jams and jellies, because of their high sugar and acidity, do not usually provide an environment in which the C. botulinum spores germinate.
Conclusion
In order to kill C. botulinum spores they must be heated under high pressure to 250 deg F for at least twenty minutes, which is not possible in an oven because the boiling point of the cake or bread will not allow it to get that high. At best the boiling point would reach 223 deg F, any higher and you may not have a palatable product.
A person could spend the next twenty years making canned breads and cakes and never have a problem with botulism. This however, will only give them a false sense of security, because if you ask them why they don’t have to worry about C. botulinum there first response is usually, “I’ve been doing this for yyyyears and I’ve nnnnever had a problem” (famous last words). While if you ask a “safety conscious” canner they will respond by saying: “I followed the instructions exactly in the USDAs “Complete Guide to Home Canning”, which has been proven to be scientifically safe”. Not knowing why your product doesn’t get botulism, is a recipe for disaster.
Even though the risk of getting C. botulinum in your product is quite rare, the consequences are to severe to ignore. It only has to happen once, and you or your loved ones, may at worst die or at best end up with life long health issues.
