Canning is a common method that has been used for centuries to preserve food from spoilage. The canning process alters the chemical make-up of food by changing the pH, salinity or moisture levels to protect against microbes, such as bacteria, mold and yeast. It limits the activity of food enzymes which also contribute to decomposition. These chemical modifications, combined with physical barriers such as cans, seals and lids, are an effective defense against decay. But the canning process has its limitations. Canning reduces the nutrient value of food. It also requires a significant investment of time and equipment, and inadequate processing or poor sanitation can result in a deadly contamination.
Loss of Nutrients
The canning process often requires cooking the food you want to preserve. Cooking stops the natural enzymatic action in fruits and vegetables that helps them to ripen in the first place. If the enzymes are not stopped, or denatured, the food will over-ripen and become spoiled. Cooking raw fruits and vegetables to prepare them for the canning process is often done by blanching—a quick 3- to 5-minute dunk in boiling water. Fruits and vegetables are rich in minerals and water soluble vitamins that leech from the foods during blanching; essentially, leaving much of the benefit of these foods behind in the boiling water bath. Further loss of nutrients, including fat-soluble vitamins, occur during the heating step of the canning process and throughout their long shelf lives. Canned fruits and vegetables have about 35 percent of the vitamins and minerals their fresh counterparts contain.
Canning requires a good deal of equipment, from glass jars to hold food to the sturdy kettles to heat-seal the goods. Some other special equipment may be required if you are planning to do pressure-canning or to preserve meats and fish. The good news is that most of the equipment can be reused, though the upfront costs can be intimidating to a novice. Pressure canners range in price from $30 to $300. Glass jars, lids and seals can be purchased out of season to defray costs but must be replenished each time you preserve. A good kettle is essential for the water-bath portion of the canning process. A stovetop model can be purchased for about $25, or you can spend $300 on the electric type. If you are not canning your own produce you will also have to factor in the cost of fresh food. Don’t forget the cost of pickling spices, herbs, sugar and salt.
The canning process can be an all-day affair, so you should take into consideration the significant time investment for preparing, processing and waiting. All equipment should be sterilized and thoroughly cooled to limit the potential for contamination. The fruits and vegetables you want to preserve should be cleaned, peeled, pared, cored, blanched or pickled prior to packing them into canning jars. The final step in canning preserves to seal them takes time as well, whether you are using a hot water bath or pressure canning.
Perhaps the biggest disadvantage to canning food is the potential for contamination. Beginners fear creating a shelf full of tainted canned goods. Proper techniques based on the acidity of the fruits and vegetables to be canned must be strictly adhered to in order to prevent contamination from yeast, mold or bacterial spores such as Clostridium botulinum, a soil-dwelling bacterium that creates a neurotoxin-causing botulism that can lead to death. Thorough cleansing of fruits and vegetables to rid them of soil, as well as careful selection of fresh produce, is imperative. Luckily, Clostridium botulinum is susceptible to high salt and acidity levels and can be destroyed when thoroughly heated. This is why conscientious attention to all steps is essential during the canning process.
References and ResourcesCenters for Disease Control and Prevention: Botulism
USDA Publications: Complete Guide to Home Canning, 2009 Revision