Approved Canning Methods: Types of Canning Jars

Three scientifically tested and approved canning methods for home food canning are pressure canning, water bath canning, and atmospheric steam canning. These methods heat food in sealed jars until it is hot enough to kill spoilage microorganisms. Heating the can allows air to be released or forced out of the cans to create an airtight vacuum seal. The most important choice for a safe product is choosing a canning method that will kill all harmful bacteria and prevent their growth during storage. Preservation methods are also called processing methods.

Pressure Canning Machine

A pressure canner is a sealed unit that, when heated, creates pressure inside, raising the temperature. Pressure canning is essential for processing low acid vegetables and meats. Low-acid vegetables include all vegetables except acidified tomatoes, pickles and sauerkraut. Low-acid foods can promote the growth of botulism spores, which can survive the boiling temperature of water. The temperature inside a weighed pressure gauge jar at 10 pounds of pressure and a dial gauge jar at 11 pounds of pressure is 240°F at sea level, which is sufficient to kill botulism spores, a potential source of deadly foodborne illnesses.

Types of Pressure Cans

Pressure measuring device with the dial has a scale, which shows the pressure inside.

• As the temperature and pressure inside the can increase, the scale rises.
• The gauges can indicate each ½ or 1 pound increment; others mark only 5-pound increments, leaving the user to determine the pounds in between.
• The dial indicator allows the user to determine pressure increments at high altitudes. At 2000 feet or lower, the pressure should be 11 pounds for meats and vegetables and 6 pounds for fruits.
• It is necessary to monitor the pressure gauge and adjust the temperature while using it to maintain the correct pressure.

У weighed tin can with gauge pressure is a weight that controls pressure.

• One type of weight is a flat disc, marked in 5, 10 and 15 pounds.
• Another type consists of three metal rings that sit on top of each other; for 5 pounds only one ring is used; an additional ring is added for every additional 5 pounds.
• When pressure is reached inside the weight, the mass will “jibble”, indicating the proper temperature inside. Some weights swing 3-4 times per minute; others sway continuously. Check the manufacturer's instructions for the canning machine you use.
• Because you can hear the rocking, you can control the pressure without having to be near the canner all the time.
• Pressure canners process meats and vegetables at 10 pounds of pressure and fruits at 5 pounds of pressure. At altitudes above 1000 feet the pressure should be increased by 5 pounds.
• Weighted calibration cans do not need to be checked for accuracy.

Boiling water cans

A water bath canner fills food jars with boiling water, transferring heat into the food jar. Fruits, acidified tomatoes, pickled foods, jams and jellies can be safely processed in a boiling water bath.

• The jars must be completely filled with boiling water.
• A stand is needed to circulate water under the jars.
• There should be room at the top of the canner to allow one to two inches of water to cover the jars.
• A lid is needed for canning.
• You can purchase a boiling water bath canner or create a water bath canner using equipment you already have. You need a pot deep enough to have room for the trivet, the jars, and at least an inch of water above the jars, as well as room for the water to simmer quickly without boiling over.
• Note: Some newer canning jars are designed for jams and jellies and are only deep enough for pint jars.

Atmospheric Steam Canning Machines

Atmospheric steam canning is the newest method approved for home food canning. Research from the University of Wisconsin shows that the steam in an atmospheric steam canner reaches the temperature of boiling water (212°F) and is as safe to process high-acid foods as boiling water.

• An atmospheric steam canner typically has a low base with a shelf and a high lid that covers the jars.
• The lid has one or two holes at the base through which steam escapes.
• The lid should be left in place and the jar should be heated to force the air out of the jar until a column of steam 6-8 inches long forms. Steam is hotter than air.
• Foods processed in boiling water can be safely processed in an atmospheric steam canner. Processing time is the same.
• Note: Foods that take longer than 45 minutes to process should not be processed in an atmospheric steam bath as this may cause the can to become overcooked.

Unsafe Canning Methods

Some canning methods that were used many years ago are no longer considered safe. Do not use these methods for home canning food.

• The open pot or hot pour method involves pouring hot food into jars and heating the food until the jars seal. It's not safe!Heat is not sufficient to kill spoilage microorganisms. This method is no longer recommended for pickles, jams, or jellies. Brief processing of these products will kill mold, yeast and bacteria in the head section. The treatment also forces air out of the cans, creating a stronger vacuum seal.
• Placing cans in an oven for processing can be dangerous because the cans may explode, causing personal injury, and the heat may not be distributed evenly within the cans. Jars are not designed for oven temperatures. Older cookbooks may contain instructions for oven canning, but this is no longer recommended.
• You can even find instructions for canning in microwaves, slow cookers, slow cookers, dishwashers, or in the sun. These methods can be extremely dangerous and are not recommended. Avoid canning powders or chemicals that try to replace heat treatment.