Safe Home Canning of Fruits, Vegetables and Meats

Section 1

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The Basics—Principles of Home Canning

Food Acidity and Processing Methods
Determining Processing Times
Why There Are More Changes in Home Canning Methods
Processing Adjustments at High Altitudes
Equipment and Methods Not Recommended

Maintaining Color and Flavor in Canned Food
Advantages of Hot-Packing Over Raw-Packing
Controlling Headspace

Jar Cleaning
Sterilization of Empty Jars
Lid Selection, Preparation, and Use

Boiling-water Canners
Pressure Canners

Canning Without Sugar
Canning Without Salt

Why People Can Foods

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Canning can be a safe and personally rewarding way to preserve quality food at home. Canning favorite and special products to be enjoyed by family and friends often is a fulfilling experience and a source of pride for many people. Canning may not be the least expensive way of obtaining every type of food and costs of equipment, energy, and time must be considered.

However, the main objective of canning is to preserve the food by the application of heat so that it can be safely eaten at a later time. Safety of the consumer is the primary concern when food is canned. It is also important to achieve acceptable quality in the final product and to retain as much of the nutritive value of the food as possible. The potential advantages of home canning are lost 1) when you start with poor quality fresh foods, 2) when jars fail to seal properly, 3) when food spoils, and 4) when flavors, texture, color, and nutrients deteriorate during prolonged storage in warm, bright light conditions.

The Nutritional Value of Canned Food

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Many vegetables begin to lose vitamins when harvested. Nearly half the vitamins may be lost within a few days unless the fresh produce is cooled or preserved. Within one to two weeks, even refrigerated produce may lose half of its vitamins. The heating process during canning destroys from 1/3 to ½ of vitamins A and C, thiamin, and riboflavin. Once canned, additional losses of these sensitive vitamins are from 5 to 20 percent each year depending on storage conditions. The amounts of other vitamins, however, are only slightly lower in canned compared with fresh food. Vegetables handled properly and canned promptly after harvest may be more nutritious than fresh produce held many days after harvest under abusive conditions.

How Canning Preserves Foods

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The high percentage of water in most fresh foods makes them very perishable. They spoil or lose their quality for several reasons:

• growth of undesirable microorganisms such as bacteria, molds, and yeasts
• activity of food enzymes
• reactions with oxygen
• moisture loss

Microorganisms live and multiply quickly on the surfaces of fresh food and on the inside of bruised, insect-damaged, and diseased food. Oxygen and enzymes are present throughout fresh food tissues. Proper canning practices minimize the effects of these microorganisms. They include:

• carefully selecting and washing fresh food
• peeling some fresh foods
• hot packing many foods
• adding acids (lemon juice or vinegar) to some foods
• using acceptable jars and self-sealing lids
• processing jars in a boiling-water or pressure canner for the correct period of time.

When these practices are followed along with recommended methods, they control potential spoilage by removing oxygen, destroying enzymes, destroying and/or preventing the growth of undesirable bacteria, yeasts, and molds, and by helping form a high vacuum in jars. Good vacuums form tight seals which keep the food in the jars and keep air and microorganisms from reentering.

The most critical step in ensuring safety in canning is processing in a boiling-water bath or pressure canner. This is what destroys microorganisms and creates the desired vacuum for a good seal. Both a high temperature and sufficient time is required to be certain of adequate heat processing. This ensures that all parts of the food being canned have received enough heat to reduce the number of microorganisms to an extremely small level. A safe food with a long storage life is produced. The complete destruction of every microorganism would result in a product with unacceptable quality and little nutritional value. A best process is that which has a maximum effect on spoilage organisms and minimal effect on quality.

Ensuring Safe Canned Foods

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Growth of the bacterium Clostridium botulinum in canned food may cause botulism, a deadly form of food poisoning. These bacteria exist either as spores or as vegetative cells. The spores, which are dormant and comparable to plant seeds, can survive harmlessly in soil and water for many years. When ideal conditions exist for growth, the spores produce vegetative cells which multiply rapidly and may produce a deadly toxin within three to four days of growth in an environment consisting of:

• a moist, low-acid food
• a temperature between 40° and 120°F
• less than 2 percent oxygen

Botulism spores are on most fresh food surfaces. Because they grow only in the absence of air, they are harmless on fresh foods. Most bacteria, yeasts, and molds are difficult to remove from food surfaces. Washing fresh food reduces their numbers only slightly. Peeling root crops, underground stem crops, and tomatoes reduces their numbers greatly. Blanching also helps, but the vital controls are the method of canning and making sure the recommended research-based process times are used.

The processing times in this publication ensure destruction of the largest expected number of heat-resistant microorganisms in home-canned foods. Properly processed, canned food will be free of spoilage if lids seal and jars are stored below 95°F. Storing jars at 50° to 70°F also enhances retention of quality.

To further reduce the risk of botulism, home canned low-acid and tomato foods should be boiled even if you detect no signs of spoilage. Boil foods for 10 minutes at altitudes below 1,000 feet. Add an additional minute of boiling time for each additional 1,000 feet elevation. In Minnesota, boil food for 11 minutes.

Food Acidity and Processing Methods

Whether food should be processed in a pressure canner or a boiling-water bath to control botulism bacteria depends on the acidity in the food. Acidity may be natural, as in most fruits, or added, as in pickled food. Low-acid canned foods contain too little acidity to prevent the growth of these bacteria. Acid foods contain enough acidity to block their growth, or destroy them more rapidly when heated. The acidity level in foods can be increased by adding lemon juice, citric acid, or vinegar.

The term "pH" is an index of acidity. The lower its value, the more acid in the food. Low-acid foods have pH values higher than 4.6. They include red meats, seafood, poultry, milk, and all fresh vegetables except for most tomatoes. Most mixtures of low-acid and acid foods also have pH values above 4.6 unless enough lemon juice, citric acid, or vinegar is included to make them acid foods. Acid foods have a pH of 4.6 or lower. They include fruits, pickles, sauerkraut, jams, jellies, marmalades, and fruit butters.

Although tomatoes usually are considered an acid food, some are now known to have pH values slightly above 4.6. Figs also have pH values slightly above 4.6. Therefore, if they are to be canned as acid foods, these products with unknown pH must be acidified to a pH of below 4.6 with lemon juice or citric acid. Properly acidified tomatoes and figs are acid foods and can be safely processed in a boiling-water bath. Processing acid foods at boiling water temperatures will destroy yeast and molds, the most common forms of spoilage microorganisms in these foods. Heat-sensitive bacteria are also killed. Those that are heat resistant, such as C. botulinum spores, are prevented from multiplying because of the high acid conditions of the food.

Botulism spores are very heat resistant. They may be destroyed at boiling water temperatures, but extremely long times are required. The higher the canner temperature, the more easily and quickly they are destroyed. Therefore, all low-acid foods should be sterilized at temperatures of 240° to 250°F, attainable with pressure canners operated at 10 to 15 PSI. PSI means pounds per square inch of pressure as measured by a gauge. At these temperatures, the time needed to destroy bacteria in low-acid canned food ranges from 20 to 100 minutes. The exact time depends on the kind of food being canned, the way it is packed into jars, and the size of jars. The time needed to safely process low-acid foods in a boiling water canner ranges from 7 to 11 hours. Such long processing times are not researched and are not recommended. Losses in nutrients and quality would be unacceptable. The time needed to process acid foods in boiling water varies from 5 to 85 minutes.

Acidity of foods helps determine the type of heat processing or home canning required for safe preservation.

Determining Processing Times

In addition to the acidity of the food and the heat resistance of the microorganism, the time required for sufficient heat to penetrate all parts of the food in the jar must be considered. Heat is transferred from the outside of the jar through the food and thus is affected by:

• The size and shape of the container. Smaller jars heat faster than wider or taller jars.
• Amount of liquid. Food containing a large amount of free liquid heats much more quickly than a more solid product.
• Piece size. Smaller pieces of food (corn, peas) heat much more quickly than large chunks.
• Amount of fat. Fat insulates the food and slows heat transfer.
• The type of heating medium being used. Wet steam heats faster than dry air.

The many factors involved make it impossible to estimate the correct processing conditions for any food product. This is especially true for items which are mixtures of food with differing water content, piece size, fat content, or acidity as well as types and numbers of microorganisms present. The establishment of a correct, safe process requires laboratory research by trained scientists.

Individuals who can food at home and do not use methods approved by the Minnesota Extension Service, other state extension services, United States Department of Agriculture (USDA), or other reputable sources (Kerr, Ball, etc.) are taking a great risk with the health of those who eat the canned product.

Why There Are More Changes in Home Canning Methods

As with many things in our society, ongoing research continues to increase our knowledge about factors affecting the safety of canned food. Combinations of incorrect ingredients, processing times unadjusted for altitude, faulty equipment, and human error may cause the home-canned food to be unsafe for consumption. The latest changes in home food preservation methods are based on research sponsored by the USDA and conducted at the Extension Service Center for Excellence, Pennsylvania State University. These methods attempt to further minimize the chance of producing an unsafe product. They are more detailed in equipment, ingredients, and procedures. Examples of new method changes are:

1. Increased processing time and/or pressure with increasing altitude. This was added because water boils at lower temperatures as altitude increases. Lower temperatures are less effective for killing potentially harmful microorganisms. Increasing the process time or canner pressure compensates for lower boiling temperatures.

2. Increased pounds pressure recommendations for weighted-gauge canners vs. dial-gauge canners. Weighted-gauge canners cannot be set for pressures between 10 and 15 PSI. If desired pressure is above 10, then the 15 PSI setting must be used.

3. Using a pressure saucepan is not recommended. Pressure saucepans have poor temperature control and a risk of inadequate heat processing. They heat up and cool down too quickly.

4. Addition of lemon juice or citric acid to tomatoes and tomato products. This ensures that the acid level is great enough to permit water bath processing or allow reduced pressure canning times. Recently a few tomato varieties have been found not to contain enough acid.

5. Increased processing times for non-water packed whole or halved tomatoes. Some new tomato varieties are more solid or have less liquid. It thus take longer to transfer heat to the coldest point in the jar and kill the microorganisms present.

6. Increased headspace for many canned vegetables. New methods have increased processing times or pounds pressure and this requires food be heated to higher temperatures. Because of this there is increased expansion of food in the jars and headspace must also be increased.

Unfortunately many home canners think these changes are too complicated or overdone. To help understand and accept these changes, you need to be able to assess and accept risks. There is a potential health risk associated with most things we do. For example, we take a risk of being in an accident when we drive or ride in a car. But we take these risks because we believe the convenience and time we save is worth it. We may choose to reduce driving risks by driving carefully or more slowly and by wearing seat belts. The same is true of the new canning methods in this manual. They involve extra details which make them more difficult and time consuming. However, the risk of food poisoning is further reduced if they are followed. These new USDA methods have been integrated into this publication with methods previously researched at the University of Minnesota and found in previous publications of the Minnesota Extension Service. In the "Tomatoes" section of this publication you are given method options from which to choose, depending on the varieties selected and the level of risk you wish to assume. No method is failure-proof or can assure 100 percent safety under all circumstances of ingredients, processing, and storage. With tomatoes, home canners are allowed to decide on the method which represents an acceptable amount of risk for an acceptable amount of time and energy spent. This risk is further reduced by boiling the food before eating.

Processing Adjustments at High Altitudes

Using the process time for canning food at sea level may result in spoilage if you live at altitudes of 1,000 feet or more. Water boils at lower temperatures as altitude increases. Lower boiling temperatures are less effective for killing bacteria. Increasing the process time or canner pressure compensates for lower boiling temperatures. The highest inhabited elevation in Minnesota (2,000 ft) is used to determine the recommended processing times found in this publication. However, if you use the charts in the new USDA Canning Guides, select the proper processing time or canner pressure for the altitude where you live. If you do not know the altitude, contact your local county Extension agent or district conservationist with the Soil Conservation Service.

Equipment and Methods Not Recommended

1. Open-kettle canning and the processing of freshly filled jars in conventional ovens, microwave ovens, and dishwashers are not recommended. These practices have great risk of producing unsafe foods.

2. Unpressurized steam canners are not recommended because processing times for use with current models have not been adequately researched. Because steam canners may not heat foods in the same manner as boiling water canners, their use with boiling-water process times may result in spoilage.

3. It is not recommended that pressure processes in excess of 15 PSI be applied when using new pressure canning equipment.

4. So-called canning powders are useless as preservatives and do not replace the need for proper heat processing.

5. Jars with wire bails and glass caps make attractive antiques or storage containers for dry food ingredients but are not recommended for use in canning.

6. One-piece zinc porcelain-lined caps are also no longer recommended. Both glass and zinc caps use flat rubber rings for sealing jars, but too often fail to seal properly.

7. Pressure saucepans, because of poor temperature control and risk of inadequate heat processing, are not recommended.

8. Devices for canning food in microwave ovens are not recommended because of incomplete destruction of bacteria due to non-uniform heating.

Ensuring High-Quality Canned Foods

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Begin with high-quality, fresh foods suitable for canning. Quality varies among different fruits and vegetables. Examine food carefully for freshness and wholesomeness. Discard diseased and moldy food. Trim small diseased or discolored areas from food.

Can fruits and vegetables picked from your garden or purchased from nearby producers when the products are at their peak of quality. This is 6 to 12 hours after harvest for most vegetables. For best quality, apricots, nectarines, peaches, pears, and plums should be ripened one or more days between harvest and canning. If you must delay the canning of other fresh produce, keep it in a shady, cool place.

Fresh, home-slaughtered red meats and poultry should be chilled and canned without delay. Do not can meat from sickly or diseased animals. Put fish and seafoods on ice after catching or buying. Clean (gut, devein, etc.) immediately and can within two days.

Maintaining Color and Flavor in Canned Food

To maintain good natural color and flavor in stored, canned food, you must:

• Remove oxygen from food tissues and jars,
• Quickly destroy the food enzymes,
• Obtain high jar vacuums and airtight jar seals.

Follow these guidelines to ensure that your canned foods retain optimum colors and flavors during processing and storage:

• Use only high-quality foods which are at the proper maturity and are free of diseases and bruises.
• Use the hot-pack method, especially with acid foods to be processed in boiling water.
• Don't unnecessarily expose prepared foods to air. Can them as soon as possible.
• While preparing a canner load of jars, keep peeled, halved, quartered, sliced, or diced apples, apricots, nectarines, peaches, and pears in a solution of ascorbic acid or Vitamin C. This procedure is also useful in maintaining the natural color of mushrooms and potatoes, and for preventing stem-end discoloration in cherries and grapes. You can get ascorbic acid in several forms:

Pure powdered form: Seasonally available among canners supplies in supermarkets. One level teaspoon of pure powder weighs about 3 grams. Use 1 teaspoon per gallon of water as a treatment solution.

Vitamin C tablets: Economical and available year-round in many stores. Buy 500-milligram tablets; crush and dissolve 6 tablets per gallon of water as a treatment solution.

Commercially prepared mixes of ascorbic and citric acid: Seasonally available among canners' supplies in supermarkets. Sometimes citric acid powder is sold in supermarkets, but it is less effective in controlling discoloration. If you choose to use these products, follow the manufacturer's directions.

• Fill hot foods into jars and adjust headspace as specified in recipes.
• Tighten screw bands securely, but if you are especially strong, not as tightly as possible.
• Process and cool jars.
• Store the jars in a relatively cool, dark place, preferably between 50° and 70°F.
• Can no more food than you will use within a year.

Many fresh foods contain from 10 percent to over 30 percent air. The length of time canned food retains high quality depends on how much air is removed from food before jars are sealed.

Raw-packing is the practice of filling jars tightly with freshly prepared, but unheated food. Such foods, especially fruit, will float in the jars. The entrapped air in and around the food may cause discoloration within two to three months of storage. Raw-packing is more suitable for vegetables processed in a pressure canner.

Hot-packing is the practice of heating freshly prepared food to boiling, simmering it 3 to 5 minutes, and promptly filling jars loosely with the boiled food. Whether food has been hot-packed or raw-packed, the juice, syrup, or water to be added to the foods should also be heated to boiling before adding it to the jars. This practice helps to remove air from food tissues, shrinks food, helps keep the food from floating in the jars, increases vacuum in sealed jars, and improves shelf life. Pre-shrinking food permits filling more food into each jar.

Hot-packing is the best way to remove air and is the preferred pack style for foods processed in a boiling water canner. At first, the color of hot-packed foods may appear no better than that of raw-packed foods, but within a short storage period, both color and flavor of hot-packed foods will be superior.

Controlling Headspace

The unfilled space above the food in a jar and below its lid is termed headspace. Directions for canning specify leaving ¼ inch for jams and jellies, ½ inch for fruits and tomatoes to be processed in boiling water and from 1 to 1¼ inches in low-acid foods to be processed in a pressure canner. This space is needed for expansion of food as jars are processed, and for forming vacuums in cooled jars. The extent of expansion is determined by the air content in the food and by the processing temperature. Air expands greatly when heated to high temperatures; the higher the temperature, the greater the expansion. Foods expand less than air when heated.

Jars and Lids

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Food may be canned in glass jars or metal containers. Metal containers can be used only once. They require special sealing equipment and are much more costly than jars.

Regular and wide-mouth, Mason-type, threaded, home-canning jars with selfsealing-lids are the best choice. They are available in ½ pint, pint, 1½ pint, quart, and ½ gallon sizes. The standard jar mouth opening is about 2-3/8 inches. Wide-mouth jars have openings of about 3 inches, making them more easily filled and emptied. To be certain of adequate processing, it is important to use only the size(s) of jar listed in the recommended method. With careful use and handling, Mason jars may be reused many times, requiring only new lids each time. When lids are used properly, jar seals and vacuums are excellent. Mason jars designed for use in home canning ensure a safe product and no breakage during processing.

Jar Cleaning

Before reuse, wash empty jars in hot water with detergent and rinse well by hand, or wash in a dish-washer. Unrinsed detergents may cause unnatural flavors and colors. These washing methods do not sterilize jars. Scale or hard-water films on jars are easily removed by soaking jars several hours in a solution containing 1 cup of vinegar (5 percent) per gallon of water.

Sterilization of Empty Jars

All jams, jellies, and pickled products processed 10 minutes or less should be filled into sterile empty jars. To sterilize empty jars, put them right side up on the rack in a boiling-water canner. Fill the canner and jars with hot (not boiling) water to 1 inch above the tops of the jars. Boil 11 minutes when at Minnesota altitudes. At higher elevations, boil 1 additional minute for each additional 1,000 feet elevation. Remove and drain hot sterilized jars one at a time. Save the hot water for processing filled jars. Fill jars with food, add lids, and tighten screw bands.

Empty jars used for vegetables, meats, and fruits to be processed in a pressure canner need not be presterilized. It is also unnecessary to presterilize jars for fruits, tomatoes, and pickled or fermented foods that will be processed 10 minutes or longer in a boiling-water canner.

Lid Selection, Preparation, and Use

The common self-sealing lid consists of a flat metal lid held in place by a metal screw band during processing. The flat lid is crimped around its bottom edge to form a trough, which is filled with a colored gasket compound. When jars are processed, the lid gasket softens and flows slightly to cover the jar-sealing surface, yet allows air to escape from the jar. The gasket then forms an airtight seal as the jar cools. Gaskets in unused lids work well for at least five years from date of manufacture.

The gasket compound in older unused lids may fail to seal on jars. Buy only the quantity of lids you will use in a year. To insure a good seal, carefully follow the manufacturer's directions in preparing lids for use. Examine all metal lids carefully. Do not use old, dented, or deformed lids, or lids with gaps or other defects in the sealing gasket.

After filling jars with food, release air bubbles by inserting a flat plastic (not metal) spatula between the food and the jar. Slowly turn the jar and move the spatula up and down to allow air bubbles to escape. Adjust the headspace and then clean the jar rim (sealing surface) with a dampened paper towel. Place the lid, gasket down, onto the cleaned jar-sealing surface. Uncleaned jar-sealing surfaces may cause seal failures.

Fit the metal screw band over the flat lid. Follow the manufacturer's guidelines enclosed with or on the box for tightening the jar lids properly.

Do not retighten lids after processing jars. As jars cool, the contents in the jar contract, pulling the self-sealing lid firmly against the jar to form a high vacuum. If rings are too loose, liquid may escape from jars during processing, and seals may fail. If rings are too tight, air cannot vent during processing, and food will discolor during storage. Overtightening also may cause lids to buckle and jars to break, especially with raw-packed, pressure-processed food.

Screw bands are not needed on stored jars. They can be removed easily after jars are cooled. When removed, washed, dried, and stored in a dry area, screw bands may be used many times. If left on stored jars, they become difficult to remove, often rust, and may not work properly again.

Equipment Used for Home Canning

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1. Range

2. Pressure canner with rack, lid, and a dial gauge or weighted gauge

3. Water bath canner with rack and lid

4. Jars, lids, and screw bands

5. Jar lifter for easy removal of hot jars from canner

6. Funnel or jar filler to pack small food items into jars

7. Bubble freer, plastic knife, or spatula. Do not use metal because it scratches glass which could cause it to break more easily

8. Lid wand with magnet on the end to remove lids from hot water when following manufacturers treatment instructions.

9. Clean cloths for wiping jars rims and general cleanup
   

10. Knives for product preparation

11. Timer or clock to determine end of processing time

12. Clean towels, rack, or board on which to cool the hot jars after processing

13. Hot pads

14. Cutting board

Selecting the Correct Processing Time

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When canning in boiling water, more processing time is needed for most raw-packed foods and for quart jars than is needed for hot-packed foods and pint jars.

The food may spoil under any of these conditions:

1. you fail to add process time for lower boiling-water temperatures at altitudes about 2,000 feet

2. you process for fewer minutes than specified

3. you cool jars in cold water

4. you fail to exhaust canners properly

5. you process at lower pressure than specified

6. you cool the canner with water

Process times for 1-1/2 pint and pint jars are the same, as are times for 1-½ pint and quart jars. For some products, you have a choice of processing at 5, 10, or 15 PSI. In these cases, choose the canner pressure (PSI) you wish to use and match it with your pack style (raw or hot) and jar size to find the correct process time.

To destroy microorganisms in acid foods, processed in a boiling-water canner, you must:

• Process jars for the correct number of minutes in boiling water
• Cool the jars at room temperature

To destroy microorganisms in low-acid foods processed with a pressure canner, you must:

• Process the jars for the correct number of minutes at 240°F (10 PSI) to 250°F (15 PSI) as the method indicates.
• Allow canner to cool at room temperature until it is completely depressurized.

Recommended Canners and Their Use

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Equipment for heat-processing home-canned food is of two main types, boiling-water canners and pressure canners. Most are designed to hold 7 quart jars or 8 to 9 pints. Small pressure canners hold 4 quart jars. Some large pressure canners hold 18 pint jars in two layers, but hold only 7 quart jars. Pressure saucepans with smaller volume capacities are not recommended for use in canning. Small capacity pressure canners are treated in a similar manner as standard larger canners, and should be vented using the typical venting procedures.

Low-acid foods must be processed in a pressure canner to be free of botulism risks. Although pressure canners may also be used for processing acid foods, it is faster to do so in boiling-water canners. A pressure canner would require from 55 to 100 minutes to can a load of jars whereas the total time for canning most acid foods in boiling water varies from 25 to 60 minutes.

Boiling-Water Canners

These canners are made of aluminum or porcelain-covered steel. They have removable perforated racks and fitted lids. The canner must be deep enough so that at least 1 inch of briskly boiling water will be over the tops of jars during processing. Some boiling-water canners do not have flat bottoms. A flat bottom must be used on an electric range. Either a flat or ridged bottom can be used on a gas burner. To ensure uniform processing of all jars with an electric range, the canner should be no more than 4 inches wider in diameter than the element on which it is heated. Follow these steps for successful boiling-water canning:

1. Fill the canner halfway with water.

2. Preheat water to 140°F for raw-packed foods (lower temperature reduces jar breakage) and to 180°F for hot-packed foods.

3. Load filled jars, fitted with lids, into the canner rack and use the handles to lower the rack into the water or fill the canner, one jar at a time, with a jar lifter.

4. Add more boiling water, if needed, so the water level is at least 1 inch above jar tops.

5. Turn heat to its highest position until water boils vigorously.

6. Set a timer for the minutes required for processing the food.

7. Cover with the canner lid and lower the heat setting to maintain a gentle boil throughout the process schedule.

8. Add more boiling water, if needed, to keep the water level above the jars.

9. When jars have been boiled for the recommended time, turn off the heat and remove the canner lid.

10. Using a jar lifter, remove the jars and place them on a towel, leaving at least one inch between the jars during cooling.

Pressure Canners

Pressure canners for use in the home have been extensively redesigned in recent years. Models made before the 1970s were heavy-walled kettles with clamp-on or turn-on lids. They were fitted with a dial gauge, a vent port in the form of a petcock or counterweight, and a safety fuse. Modern pressure canners are lightweight, thin-walled kettles which usually have turn-on lids. They have a jar rack, gasket, dial or weighted gauge, an automatic vent/cover lock, a vent port (steam vent) to be closed with a counterweight or weighted gauge, and a safety fuse.

Pressure does not destroy microorganisms. High temperatures applied for a certain period of time kill microorganisms. The success of destroying all microorganisms capable of growing in canned food is based on the temperature obtained in pure steam, free of air, at sea level. At sea level, a canner operated at a gauge pressure of 10 pounds provides an internal temperature of 240°F.

Two serious errors in temperatures obtained in pressure canners occur because:

1. Internal canner temperatures are lower at higher altitudes. To correct this error, canners must be operated at the increased pressures specified in this publication for the appropriate altitude.

2. Air trapped in a canner lowers the temperature obtained at 5, 10, or 15 pounds of pressure and results in underprocessing. The highest volume of air trapped in a canner occurs in processing raw-packed foods in dial-gauge canners. These canners do not vent air during processing. To be safe, all types of pressure canners must be vented 10 minutes before they are pressurized.

To vent a canner, leave the vent port uncovered on newer models or manually open petcocks on some older models. Heating the filled canner with its lid locked into place boils water and generates steam that escapes through the petcock or vent port. When steam first escapes, set a timer for 10 minutes. After venting 10 minutes, close the petcock or place the counterweight or weighted gauge over the vent port to pressurize the canner.

Weighted-gauge models exhaust tiny amounts of air and steam each time their gauge rocks or jiggles during processing. They control pressure precisely and need neither watching during processing nor checking for accuracy. The sound of the weight rocking or jiggling indicates that the canner is maintaining the recommended pressure and needs no further attention until the load has been processed for the set time. The single disadvantage of weighted-gauge canners is that they cannot correct precisely for higher altitudes. At altitudes above 1,000 feet they must be operated at canner pressures of 10 instead of 5, or 15 instead of 10 PSI.

Check dial gauges for accuracy before use each year. Contact your local county extension office for gauge testing times and places and replace the gauge if it reads high by more than 1 pound at 5, 10, or 15 pounds of pressure. Low readings cause overprocessing and may indicate that the accuracy of the gauge is unpredictable.

Handle canner lid gaskets carefully and clean them according to the manufacturer's directions. Nicked or dried gaskets will allow steam leaks during pressurization of canners. Keep gaskets clean between uses. Older canner models may require a light coating of vegetable oil once a year. Newer models are prelubricated and do not need oiling. Check your canner's instructions if you are unsure whether or not your canner lid has been prelubricated.

Safety fuses found in the lid are thin metal inserts or rubber plugs designed to relieve excessive pressure from the canner. Do not pick at or scratch fuses while cleaning lids. Use only canners that have the Underwriter's Laboratory (UL) approval to ensure their safety. Avoid purchasing pressure canners made in foreign countries or old used canners which are no longer manufactured. Replacement parts are difficult or impossible to obtain and the canner may be unsafe to operate.

Boiling-Water Canner

Replacement gauges and other parts for newer canners are often available at stores offering canner equipment or from canner manufacturers. When ordering parts, give your canner model number and describe the parts needed. Follow these steps for successful pressure canning:

1. Put 2 to 3 inches of hot water in the canner. Place filled jars on the rack, using a jar lifter. Fasten canner lid securely.

2. Leave weight off vent port or open petcock. Heat at the highest setting until steam flows from the petcock or vent port.

3. Maintain high heat setting, exhaust steam 10 minutes, and then place weight on vent port or close petcock. The canner will pressurize during the next 3 to 5 minutes.

4. Start timing the process when the pressure reading on the dial gauge indicates that the recommended pressure has been reached, or when the weighted gauge begins to jiggle or rock.

5. Regulate heat under the canner to maintain a steady pressure at or slightly above the correct gauge pressure. Quick and large pressure variations during processing may cause unnecessary liquid losses from jars. Weighted gauges on Mirro canners should jiggle about 2 or 3 times per minute. On Presto canners, they should rock slowly throughout the process.

6. When the timed process is completed, turn off the heat, remove the canner from heat if possible, and let the canner depressurize. Do not force-cool the canner. If you cool it with cold running water in a sink, or open the vent port before the canner depressurizes by itself, liquid will spurt from jars, causing low liquid levels and jar seal failures. Force-cooling may also warp the canner lid of older model canners, causing steam leaks. Depressurization of older models should be timed. Standard size heavy-walled canners require about 30 minutes when loaded with pints and 45 minutes with quarts. Newer thin-walled canners cool more rapidly and are equipped with vent locks. These canners are depressurized when their vent lock piston drops to a normal position.

7. After the vent port or petcock has been open for 2 minutes, unfasten the lid and remove it carefully. Lift the lid away from you so that the steam does not burn your face.

8. Remove jars with a lifter, and place on towel or cooling rack, if desired.

Pressure Canner

Cooling Jars

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When you remove hot jars from a canner, do not retighten their jar lids. Retightening of hot lids may cut through the gasket and cause seal failures. Cool the jars at room temperature for 12 to 24 hours. Jars maybe cooled on racks or towels to minimize heat damage to counters. The food level and liquid volume of raw-packed jars will be noticeably lower after cooling. Air is exhausted during processing and food shrinks. If a jar loses excessive liquid during processing, do not open it to add more liquid. Check for sealed lids as described below.

Testing Jar Seals

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After cooling jars for 12 to 24 hours, remove the screw bands and test seals with one of the following options:

Option 1.Press the middle of the lid with a finger or thumb. If the lid springs up when you release your finger, the lid is unsealed.

Option 2.Tap the lid with the bottom of a teaspoon. If it makes a dull sound, the lid is not sealed. If food is in contact with the underside of the lid, it will also cause a dull sound. If the jar lid is sealed correctly, it will make a ringing, high-pitched sound.

Option 3.Hold the jar at eye level and look across the lid. The lid should be concave (curved down slightly in the center). If the center of the lid is either flat or bulging, it may not be sealed.

Reprocessing Unsealed Jars

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If a jar fails to seal, remove the lid and check the jar-sealing surface for tiny nicks. If necessary change the jar, add a new, properly prepared lid, and reprocess within 24 hours using the same processing time.

Headspace in unsealed jars may be adjusted to 1½ inch and jars could be frozen instead of reprocessed. Foods in single unsealed jars could be stored in the refrigerator and consumed within several days.

Storing Canned Foods

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If lids are tightly vacuum sealed on cooled jars, remove screw bands, wash the lid and jar to remove food residue, then rinse and dry jars. Label and date the jars and store them in a clean, cool, dark, dry place. Do not store jars above 95°F or near hot pipes, a range, a furnace, in an uninsulated attic, or in direct sunlight. Under these conditions, food will lose quality in a few weeks or months and may spoil. Dampness may corrode metal lids, break seals, and allow recontamination and spoilage.

Accidental freezing of canned foods will not cause spoilage unless jars become unsealed and recontaminated. However, freezing and thawing may soften food. If jars must be stored where they may freeze, wrap them in newspapers, place them in heavy cartons, and cover with more newspapers and blankets.

Identifying and Handling Spoiled Canned Food

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Do not taste food from a jar with an unsealed lid or food which shows signs of spoilage. You can more easily detect some types of spoilage in jars stored without screw bands. Growth of spoilage bacteria and yeast produces gas which pressurizes the food, swells lids, and breaks jar seals. As each stored jar is selected for use, examine its lid for tightness and vacuum. Lids with concave centers have good seals. Next, while holding the jar upright at eye level, rotate the jar and examine its outside surface for streaks of dried food originating at the top of the jar. Look at the contents for rising air bubbles and unnatural color.

While opening the jar, smell for unnatural odors and look for spurting liquid and cottonlike mold growth (white, blue, black, or green) on the top food surface and underside of lid.

Carefully discard any jar of spoiled food to prevent possible illness to you, your family, and pets. You must detoxify the container, lid, and all the contents before disposal. To do so, place container with contents and lid on their sides in an 8-quart or larger stock pot, pan, or boiling-water canner. Wash your hands thoroughly. Add water to the pot so it is 1 inch or more above everything in the pot. Avoid splashing the water. Place a lid on the pot and heat the water to boiling. Boil 30 minutes to ensure detoxification of the food, container, and lids. Cool and discard the food, container, and all container components such as lids in the trash or bury in soil. Take care that animals or children cannot get in contact with the disposed food and containers. Thoroughly wash all counters, containers, and equipment including can opener, clothing, and hands that may have been in contact with the food or containers. Discard any sponges or wash cloths used in cleaning. Place all in a plastic bag and discard in the trash where they are unreachable by animals and children. This will prevent accidental poisoning.

Canning Foods for Special Diets

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The high cost of commercially canned, special diet food often prompts interest in preparing these products at home. Some low-sugar and low-salt foods may be easily and safely canned at home. However, the color, flavor, and texture of these foods may be different than expected and be less acceptable.

Canning Without Sugar

When canning regular fruits without sugar, it is very important to select fully ripe but firm fruits of the best quality. Prepare these as hot packs as described later in this publication, but use water or regular unsweetened fruit juices instead of sugar syrup. Juice made from the fruit being canned is best. Blends of unsweetened apple, pineapple, and white grape juice are also good for filling over solid fruit pieces. Adjust headspaces and lids and use the processing recommendations given for regular fruits. Add sugar substitutes, if desired, when serving.

Canning Without Salt

To can tomatoes, vegetables, meats, poultry, and seafood, use the procedures given later in this publication, but omit the salt. In these products, salt seasons the food but is not necessary to ensure its safety. Add salt substitutes, if desired, when serving.

Canning Baby Foods

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You may prepare any chunk-style or pureed fruit with or without sugar, using the procedure for preparing and processing found in this publication. Pack in half-pint, preferably, or pint jars and use the following processing times for all Minnesota altitudes.

Recommended Process: Boiling-Water Bath÷Half-Pints or Pints, Hot Pack, 25 minutes

Caution: Do not attempt to can pureed vegetables, red meats, or poultry because proper processing times for pureed foods have not been determined for home use. Instead, can and store these foods using standard processing procedures. Puree or blend them at serving time. Heat the blended foods to boiling, simmer for 10 minutes, cool, and serve. Store unused portions in the refrigerator and use within two days for best quality.

The Amount You Should Can

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The amount of food to can or freeze for your family should be decided by your family. The following formula might be helpful in calculating your needs.

Use the suggested serving size for a particular food as listed below. Multiply this amount by the number of family members who will be eating this food. Then multiply this by your estimate of the number of servings per week per person. Multiply this figure by 52 weeks to get a total amount necessary to preserve in one year. To get this amount in quarts, multiply the number by four.

Example:
Fruit—½ cup suggested serving X 4 family members = 2 cups.
Two cups X 3 servings per week per person = 6 cups/week.
Six cups X 52 weeks/year = 312 cups.
Divided by 4 = 78 quarts.

Suggested Serving Sizes

Fruits	½ cup
Juices	1 cup
Vegetables	½ cup
Meat & Seafood	½ cup
Soups	1 cup
Sauces	½ cup

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