Canned Breads and Cakes
Answer - Recipes for canned breads and cakes as gift items seem to appear each year around Christmas time. These products are typically made by pouring batter into glass canning jars and baking them in the oven. Once the cake or bread is done, the steaming jars are taken out of the oven and then sealed and cooled to create a vacuum. Most recipes claim that they can be stored without refrigeration for about a year. Some say they will keep indefinitely.
The microorganism we are concerned about in these products is Clostridium botulinum. If spores of this type of bacteria are allowed to germinate and grow, deadly botulism toxin is produced. Very small amounts of the toxin can cause an often fatal disease called botulism. Clostridium botulinum spores are abundant in nature but fortunately will only grow and produce toxin in unrefrigerated high moisture foods that are low in acid and exposed to little or no oxygen. These conditions occur in canned foods such as asparagus, green beans, beets, and corn. Thus low-acid canned foods must be processed in pressurized retorts at temperatures of 240 degrees F or higher to make sure that the heat resistant spores are killed.
Outbreaks of botulism from more unusual sources have been reported such as garlic in oil mixtures, improperly handled baked potatoes wrapped in aluminum foil, and home-canned or fermented fish. Some research studies have shown that low acid canned bread or cake products may have characteristics that are favorable for growth of Clostridium spores.
Several years ago, a professor of Food Science at Penn State developed a recipe for canned bread. It was carefully formulated so that acid and moisture levels would prevent the growth of Clostridium botulinum spores during room temperature storage. The product can be safely made as long as the original Penn State recipe is followed exactly as written. However, there is a significant risk that the creative cook may make ingredient substitutions or omissions that could significantly change the pH of the product such that conditions might be more favorable for growth of Clostridium spores.
In addition to the risk of botulism, there is also a significant risk for consumers to become injured from broken glass when baking cakes and breads in glass canning jars. Canning jars are intended for use in hot water baths or pressure canners. They are not designed to withstand the thermal stresses that occur with dry oven heat.
Therefore, Penn State strongly discourages consumers from canning cakes and breads in jars. Botulism is a serious and often fatal disease and no consumer should take unnecessary risks with this microorganism. If someone gives you a home canned cake or bread product, assume that it is unsafe to eat and discard the contents.
References and additional information
- Canning Breads and Cakes, University Of Georgia Cooperative Extension
- Safety of Canning Quick Breads, Utah State University Extension
- Botulism, Centers for Disease Control and Prevention
- Growth of Clostridium sporogenes PA 3679 in home-style canned quick breads. Aramouni, F. M., K. K. Kone, J.A. Craig and D.Y. C. Fung. 1994. J. Food Protection 57: 882-886.
The safety of a home-style canned quick bread was investigated using spores of Clostridium sporogenes putrefactive anaerobe (PA) 3679. Baking was done at 177 degrees C for 30, 40 and 50 min, at 191 degrees C for 45, 50 and 55 min, and at 204 degrees C for 40, 45 and 50 min. Products were analyzed for pH, water activity (aw) and vacuum level. The microbial quality of the products was determined before and after baking. Of the products baked at 177 degrees C, some were stored for 90 days at room temperature (23 to 25 degrees C) or in an incubator at 35 degrees C to study their shelf-life. Inoculated and endogenous vegetative cells and their spores were counted before and after baking and after storage using Fung's Double Tube method. Results showed germination of endogenous spores in uninoculated products after baking at 177 degrees C for 30 min and storage at 35 degrees C for 90 days. Survival of inoculated C. sporogenes PA 3679 was detected for all baking and storage treatments. Further work is recommended to determine safe processing procedures for this type of product.