Pressure Canning Introduction
Abundant fresh fruits, vegetables, meats, poultry, and seafood are savored during the peak of the season and safely preserved to enjoy all year. What was once done out of necessity, today has become an opportunity to take control of the food you and your family consume. These beautiful jars of home-canned goodness will give you the satisfaction of knowing the quality and freshness of the food in your pantry. They will also ease your meal planning and take a bite out of your garbage and recycling needs. Reusable jars and bands can be used for many years. The flat lid is the only piece to be discarded. Home canning is well worth the effort when you take that first delightful bite of food canned in your own kitchen!
If you're a novice to pressure canning, this outline will give you basic knowledge of the terminology and instruction of canning. The key to successful canning is to understand the acidity and spoilage factor of the food you wish to can, as well as the acceptable canning methods to process those foods. Invisible microorganisms exist naturally on fruits, vegetables, meat, poultry, and seafood. Yet they are not a problem unless food is left to sit for extended periods of time, causing food spoilage. This is nature's way of telling us when food is no longer fit to eat.
There are four basic agents of food spoilage — enzymes, mold, yeast, and bacteria. Canning will interrupt the natural spoilage cycle so food can be preserved safely.
Molds, yeast, and enzymes are destroyed at temperatures below 212°F, the temperature at which water boils (except in mountainous regions). Therefore, boiling water canning is sufficient to destroy those agents.
Bacteria, however, are not as easily destroyed. The bacterium Clostridium botulinum produces a spore that makes a poisonous toxin which causes botulism. This spore is not destroyed at 212°F. In addition, this bacterium thrives on low acid foods in the absence of air. Therefore, for a safe food product, low-acid foods need to be processed at 240°F, a temperature only achieved with pressure canning.
Determining the Method
The level of acidity in the food being canned determines which method of canning is required, either boiling water canning or pressure canning. For the purpose of home canning, foods are categorized as low acid and high acid.
Low acid: Foods that are low acid have a pH value higher than 4.6 and include vegetables, meats, poultry, and seafood. Low acid foods must only be processed using the pressure canning method.
High acid: Foods that are high acid have a pH value of 4.6 or less and include fruits, jams and jellies, properly pickled vegetables and properly acidified tomatoes. Most fruits are naturally high acid. Pickles and tomatoes, which are not high acid, are made high acid with the addition of lemon juice or vinegar. High acid foods can be safely processed using the boiling water method.
Although fruits and tomatoes can be safely processed using the boiling water method, both can be acceptably canned using the pressure canning method. Always follow the processing method stated in the recipe.
Prior to the canning season thoroughly examine your pressure canner. Whether you have a new canner or a trusted old canner, it's important to do a trial run with water to ensure it is functioning acceptably. As a general rule, replace the sealing ring and over-pressure plug every two to three years. If your canner has a dial gauge, we recommend having it tested at your county extension office or with the manufacturer to ensure its proper operation. Finding a problem when there is a load of vegetables in the canner can be disheartening and wasteful.
Acceptable: All Presto® Pressure Canners will work on electric coil and regular gas ranges. Current models of Presto® Pressure Canners will also work on glass/smooth top ranges.
Although Presto believes that current pressure canners are acceptable for use on glass top stoves we recommend that you check with the owner's manual for your range or the manufacturer before using. Please be mindful of the following tips for successful use of the canner on your glass top range:
- Use the largest element, making sure that the surface of the canner bottom contacting the element does not extend more than one inch outside the element.
- Do not place the canner on two heated elements at the same time.
- Make sure that the canner does not boil dry.
- Do not use the canner on the elements for several hours at a time.
- To prevent scratches to the glass top make sure that the bottom of the canner does not have scratches or areas that are rough, and do not slide or rotate the canner on the smooth top range.
- Clean the cooking surface with a ceramic cook top cleaner prior to and after using the canner.
Before you begin
Assemble all ingredients, supplies, and equipment needed for your canning project. Carefully read, understand, and follow the recipe and canning instructions as directed. Do not substitute or omit ingredients. Always follow specific manufacturer's instructions.
Glass home cannng jars, sometimes referred to as Mason jars, are made of heat-tempered glass for durability and reuse. These are the only jars recommended for safe home canning. They are available in standard sizes (half-pint, pint and quart jars) and will withstand the heat of a pressure canner, time after time. Note: Half gallon jars are recommended only for canning clear juices, such as grape and apple.
Glass home canning jars offer a deep neck and wide sealing surface to assure a tight seal. Always visually examine canning jars for nicks or cracks. Recycle or discard any damaged jars. Do not use jars from commercially prepared foods because they were made for single-use only. Always use the jar size and exact processing procedures indicated in the research-tested processing recipe.
Preparing Jars for Canning
Jars should be thoroughly washed in hot, sudsy water. Do not use wire brushes, abrasive materials, or cleansers because they may damage the glass. Rinse jars completely with hot water. To help prevent jar breakage, allow jars to stand in very hot water prior to filling with food. A dishwasher may also be used. Wash and dry jars using a regular cycle. When cycle is complete, remove one jar at a time, keeping the rest of the jars heated until needed.
Jars do not need to be sterilized unless the food placed in them will be processed less than 10 minutes using the boiling water method, such as jams and jellies. To sterilize the jars, boil them for 10 minutes. If you live at an altitude of 1,000 feet or more, boil an additional minute for each 1,000-foot increase in altitude. If you wish, rather than sterilizing jars the processing time can be increased to 10 minutes for those jams and jellies that have a processing time of 5 minutes. The additional processing time is not harmful to most gels. Keep in mind that if your altitude is above 1,000 feet the processing time needs adjustment.
Canning Lids and Bands
The two-piece vacuum cap (lid and band) is the recommended closure for home canning. It consists of a flat metal lid with a sealing compound on the outer edge and a separate metal screw band that secures the lid during processing. The bands can be used repeatedly if they remain in good condition; however, new lids must be used each time. Always prepare lids and bands according to manufacturer's instructions.
Avoid closures such as zinc caps and glass lids that require a jar rubber. These closures do not provide a proper method to determine if the seal is safe. Also, avoid commercial one-piece caps even if they have a rubber-like gasket because they are intended for one-time use only.
Selecting and Preparing Food
Select only produce that is at its peak quality. Produce that is over-ripe or damaged will not be a good canned product. Always follow exact preparation instructions such as peeling, slicing, chopping, puréeing. Altering the recipe may affect the heat penetration of the food which when canned may result in underprocessing.
There are two methods of packing food into jars: raw pack and hot pack. Recipes will indicate a packing method that is best for the food being canned. If given a choice, the hot pack method yields better color and flavor, especially when foods are canned using the boiling water method.
Raw Pack: Unheated food is put directly into the jars and then covered with boiling water, juice or syrup. When raw packing meat, poultry, fish, and seafood, do not cover with liquid. Food should be packed tightly in the jars because it will shrink during processing. However, corn, lima beans, peas, and potatoes expand during processing and should be packed loosely.
Hot Pack: Food is heated to boiling or cooked according to recipe before being packed into jars. The food is then covered with the boiling liquid. Foods that are hot packed should be put into the jars loosely because shrinkage will not occur during processing. Precooking the food allows it to conform to the jar better for a tighter, more efficient fit and prevents food from floating up in the jar during processing.
All recipes will indicate the amount of headspace necessary for the food being canned. Headspace is the air space between the top of the food or its liquid and the lid. Leaving too much headspace can result in under processing because it may take too long to release the air from the jar. Leaving too little headspace will trap food between the jar and the lid and may result in an inadequate seal. As a general rule, allow 1/2-inch headspace for fruits and tomatoes and 1-inch for vegetables, meats, poultry, and seafood.
Removing Air Bubbles
After food has been packed in jars, work quickly to remove air bubbles that have become trapped between pieces of food by moving a clean, nonmetallic spatula around the jar between the food and side of the jar. The use of metal utensils can damage canning jars and should be avoided.
Preparing Jar Rims and Adjusting Lids
Immediately wipe jar rims with a clean, damp cloth to remove any residue. Place flat lid on rim of jar making sure sealing compound is touching glass. Position a band over the lid and screw onto the jar just until resistance is met. Not too tight, as air must release from the jars during processing and cooling. When all the air is released, a vacuum is formed and the lid seals.
The Boiling Water Method
See Boiling Water Method for your Pressure Canner.
The Pressure Canning Method
Follow the manufacturer's instructions for your specific canner.
Venting: Venting, also referred to as "exhausting," the canner is an important step in pressure canning. During the venting period, air is removed from the canner and jars creating a pure steam environment.
After loading the jars in the canner, secure the canner cover. Leave the pressure regulator off the vent pipe. Turn the heat setting to high and wait for a steady, strong flow of steam to come from the vent pipe. Allow steam to flow for 10 minutes. At the end of 10 minutes place the pressure regulator on the vent pipe.
For older model pressure canners that are equipped with petcocks, load the jars in the canner and secure the canner cover. Rotate the petcock screw to the open position. Turn the heat setting to high and wait for a steady, strong flow of steam to come from the petcock. Allow steam to flow from the petcock for 10 minutes. At the end of 10 minutes rotate the petcock screw to the closed position.
Processing: Follow the research-tested recipe for exact pressure and timing. When processing time is complete, remove canner from heat source. Allow pressure in the canner to drop naturally. Once the air vent/cover lock drops you can remove the pressure regulator from the vent pipe. Allow the canner to cool for an additional 10 minutes before removing cover.
Carefully open cover and remove jars from canner with a jar lifter making sure to not tilt the jars. Place jars on a dry towel on countertop away from drafts leaving 1 to 2 inches of space between jars to allow for even cooling. Do not invert jars or cover with a cloth. Allow jars to cool naturally to room temperature. Allow the jars to completely cool for 12 to 24 hours before checking the seals. It is important to test the seals to be sure a vacuum has been formed. Press down on the center of the lid. If it is concave, or stays down when pressed, the jar is properly vacuum sealed. See Pressure Canning Q & A if a jar fails to seal or if you have any other canning questions.
Storing Canned Food
Remove bands. Wipe off any food residue from lids and jars. Do not replace bands as they may rust and become difficult to remove. Store canned food in a cool, dark, and dry place, between 50° and 70°F. Home canned food can be kept for many years. However, after one year the quality will begin to deteriorate. For this reason, always date and label jars before storing.
If up-to-date instructions and processing times and pressures are followed carefully, spoilage is uncommon. However, it is still recommended to check for signs of spoilage before tasting any canned food. Check for a broken seal, gassiness when opening, mold, sliminess, cloudiness, or unpleasant odors. If any of these signs are present, discard the food. As a safeguard against using canned low-acid and tomato products which may be affected with spoilage that is not readily detected, boil food 10 minutes for altitudes up to 1,000 feet above sea level. Extend the boiling time by 1 minute for each 1,000 foot increase in altitude. Many times odors that cannot be detected in the cold product will become evident by this method. If, after boiling, food does not smell or look right, discard it without tasting.