Home canning or bottling, also known colloquially as putting up or processing, is the process of preserving foods, in particular, fruits, vegetables, and meats, by packing them into glass jars and then heating the jars to create a vacuum seal and kill the organisms that would create spoilage. Though ceramic and glass containers had been used for storage for thousands of years, the technique of canning, which involves applying heat for preservation, was only invented in the first decade of the 1800s. Before that, food storage containers were used for non-perishable foods, or with preservatives such as salt, sugar, vinegar, or alcohol.
Techniques The two methods of home canning are water bath canning and pressure canning. Both involve placing the food inside special glass canning jars and then heating the contents. Home canning glass jars are annealed during manufacture to increase their ability to withstand temperature changes and mechanical shocks. There are several regional variations on jar design, such as Mason jars (North America), Fowler's Vacola jars (Australia), Kilner jars (England), and Weck jars (Germany).
Water bath canning Water bath canning is appropriate for high-acid foods only, such as jam, jelly, most fruit, pickles, and tomato products with acid added. It is not appropriate for meats and low-acid foods such as vegetables. This method uses a pot large enough to hold and submerge the glass canning jars. Food is placed in glass canning jars and placed in the pot. Hot water is added to cover the jars. Water is brought to a boil (212 °F (100 °C)) and held there for at least 10 minutes. Different foods require a different length of time under boil; larger jars require longer times.
Pressure canning Pressure canning is the only safe home canning method for meats and low-acid foods. This method uses a pressure canner — similar to, but heavier than, a pressure cooker. A small amount of water is placed in the pressure canner and it is turned to steam, which without pressure would be 212 °F (100 °C), but under pressure is raised to 240 °F (116 °C). Based on the recipe, the canner is heated until the correct pressure is reached, and the jars left for the appropriate amount of time (charts have been published with times and pressures). The heat is turned off, pressure reduced, canner opened, and hot jars carefully lifted out and placed on an insulated surface (towels, wood cutting board, etc.) and out of drafts to cool.
Safety While it is possible to safely preserve many kinds of foods, home canning can expose consumers to botulism and other kinds of food poisoning if done incorrectly. The most common source of foodborne botulism is home-canned foods prepared in an unsafe manner. Safety measures must be taken when performing home canning, since ingestion of toxin in food produced by Clostridium botulinum can cause death. Because of the high risk of illness or death associated with improper canning techniques, the United States Department of Agriculture (USDA) considers it critical that consumers who intend to can at home obtain proper and current information from a reliable source. At the basis of these recommendations is the balance between bringing the food to a high enough temperature for a long enough time that spoilage and disease-producing microorganisms are killed, while not heating the food so much that it loses nutritive value or palatability.
Unsafe methods
The following methods have been determined to be unsafe food preservation techniques:
Open-kettle — Heating food in an open kettle, then pouring into jars, closing with a lid, and not further processing. Oven canning Dry canning — Processing dry goods or vegetables without the addition of liquids in an oven Canning food in a microwave oven, slow cooker or pressure cooker Canning powders — alleged preservatives. They do not replace the need for proper heat processing. Atmospheric steam canning — Processing with 100 °C steam, not under pressure Use of vintage style sealing materials such as jars with wire bails and glass caps, or zinc caps with rubber rings. Instead of a lid, cellophane and rubber bands (moldy). Using the water bath technique for low-acid foods (foods with pH greater than 4.6). Otherwise correct water bath or pressure canning but processing for too little time, the wrong pressure, or not considering variations in time/pressure due to altitude. Re-using one-use seals Using cracked or chipped jars
North America
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