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FREQUENTLY ASKED QUESTIONS   CANNING BASICS

Go to questions section:     CANNING 101     CANNER USE     FOOD SPECIFIC

CANNING 101 QUESTIONS

Question 11. I just got a pressure canner. How do I get started?

First, we strongly recommend doing an initial “water test”  or “trial run” to experience the pressure canning steps, but with water only; no jars yet. To get started, read through the instruction manual to understand how to clean the parts and how the canner operates. Add water to the pot as directed below. There is no need to place jars in the canner. This process allows you to become familiar with each step and how long it will take at your altitude. If there is a problem, you can fix it before you have food in the canner.

Stovetop Presto® Pressure Canners Water Test: Follow the instructions for pressure canning, but use only 1 quart of water for this test. Continue with the directions for heating and venting. Then bring the canner to 10 or 11 pounds pressure (depending on canner type). Read the instructions on how to maintain the proper pressure. (If the canner cannot build pressure, check for steam escaping anywhere other than under the regulator.) Turn the burner to OFF and remove the canner from the heat source. Continue to follow the instructions for cooling the canner naturally.

Presto Precise® Digital Pressure Canner Trial Run: Follow the instructions for pressure canning, using 3 quarts of water as directed. Select the pressure canning method and a short processing time, then press the advance → button. Follow the instructions throughout the canning method, pressing advance when directed to move through all of the steps. An error code will alert you if something is wrong.

Second, visit the Canning Index and read through the Canning Introduction, Frequently Asked Questions, and Canning Basics of the food you will be canning.

Question 22. Is it safe to use canning recipes found on the web or passed down from family?

Oftentimes canning problems arise because of outdated recipes. Family recipes and many found online may be seriously incorrect. Guidelines have changed, testing has changed, and agriculture is different than it was years ago. Always use reliable sources that offer current, research-tested procedures, recipes, and timetables. Such information is available on this Presto website. In addition, the National Center for Home Food Preservation and your local Cooperative Extension Service are also reliable sources of home canning information and established processing procedures. Canning recipes must be scientifically tested, which is vital to a safe and successful home canning project. Canning information published before 1994 may be incorrect and could pose a serious health risk.

Question 13. Why is it necessary to use a pressure canner for certain types of food?

Canning destroys the natural enzymes, molds, yeasts, and bacteria that cause food spoilage. Most of these microorganisms are killed by processing food at boiling temperature (212°F) for a specified time period. The temperature and time required to destroy bacteria is determined in part by the acidity of the food being canned. Along with heat, the natural acid in fruits and tomatoes retards bacteria growth.

Some bacteria, such as Clostridium botulinum, can be more difficult to destroy so canning at a higher temperature is absolutely necessary. Low-acid foods (vegetables, meats, poultry, and fish) must be canned at a temperature of 240°F or higher and held there for the time specified in the recipe in order to destroy the bacterial spores naturally present in these foods.

Pressure canning utilizes pressurized steam to reach this superheated temperature. Therefore, the United States Department of Agriculture recommends pressure canning as the only safe method for preserving low-acid foods. Low-acid foods must be canned at pressures and times stated in current, reliable, published canning instructions.

Question 34. How should pickled food and jams and jellies be canned?

Pickles, pickled vegetables (such as beets), sauerkraut, jams, jellies, and salsas should NOT be canned under pressure. They should only be preserved by using the boiling water method. To learn how to use your Presto® pressure canner as a boiling water canner, go to the Boiling Water Method.

Question 45. Is there a problem with canning overripe food?

Yes. Flat sour is a type of food spoilage that is caused by canning overripe food or allowing precooked foods to stand in the jar too long before processing. Use ripe or slightly underripe food and properly process, cool, and store. Flat sour shows no indication of spoilage until the jar is opened.

Question 56. Why do I need to use “Mason” jars?

Glass home canning jars, sometimes referred to as Mason jars, are the only jars recommended for safe home canning. They are available in standard sizes (half-pint, pint, and quart) 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.

Question 67. Do I really need to leave a certain amount of headspace in the jar?

Yes. Leaving the specified amount of headspace in a jar is important to assure a vacuum seal. If too little headspace is allowed, the food may expand and bubble out when air is being forced out from under the lid during processing. The bubbling food may leave a deposit on the rim of the jar or the seal of the lid and prevent the jar from sealing properly. If too much headspace is allowed, the food at the top is likely to discolor. More importantly, the jar may not seal properly because there will not be enough processing time to drive all the air out of the jar. See Canning Introduction.

Question 78. How do I know if the screw band is tight enough?

Do not use undue exertion. Adjust two-piece vacuum caps by screwing the bands down evenly and firmly until a point of resistance is met, or fingertip-tight. Two-piece vacuum caps seal by the cooling of the contents, not through the pressure of the screw band on the lid. During processing, the flexible metal lid permits air to be exhausted from the jar.

Question 89. Water is present on the lids when I remove the processed jars from the canner. Should I tilt the jar to remove the water?

No. The water will evaporate on the hot lid. Keep the jar upright when removing it from the canner. Tilting the jar could leave a deposit between the jar and the lid preventing the jar from sealing properly.


 

CANNER USE QUESTIONS

Question 91. How do I can with an induction range?

Presto manufactures a special Induction Compatible Pressure Canner that is equipped with a stainless steel clad base for use on induction stoves. This extra-large and extra versatile canner also works with gas, electric, and smooth top ranges for use with both pressure canning and boiling water canning. Another option to consider is the Presto Precise® Digital Pressure Canner which is electric and doesn’t require a stove.

Question 102. Where can I find information on the Presto Precise® Digital Pressure Canner?

Check out the Product page on GoPresto.com. There is also detailed information on the Canner Comparison Guide in the Canning Index that you may find useful.

Question 113. How do I stack a second layer of jars?

For some canner models, it may be necessary to double-deck pint or half-pint jars to reach the maximum capacity of your canner. It is recommended that you stagger the jars by placing one jar on top of two. The canning rack which accompanied your Pressure Canner must be placed on the bottom of the canner to prevent jar breakage. It is not necessary to use a rack between the layers of jars. However, if you wish to do so, go to Parts & Service and search for your canner’s accessories to order a rack.

Question 124. Is it necessary to vent my pressure canner before processing?

Yes. It is vitally important to allow steam to escape from the canner for 10 minutes before placing the pressure regulator on the vent pipe. This ensures that all air is vented (exhausted) from the canner as well as the jars. If the air is not exhausted, the inside temperature may not correspond to the pressure on the gauge. It also eliminates any air pockets in the jars of food that would cause an uneven heat treatment to occur.

Question 135. Do I use the same time and pressure when processing less than a full load in the
canner?

Yes. The processing pressure and time, as well as water in the canner must be the same regardless of the number of jars being processed. The venting (exhausting) time also remains the same.

Question 86. On my Weighted Gauge Canner with 3-piece adjustable regulator, why is it important for 
the pressure regulator to maintain a slow, steady rocking motion?

Question 8

The adjustable pressure regulator is designed to maintain the appropriate pressure inside the canner when the regulator is rocking in a slow and steady motion. A loud, annoying, and vigorously rocking regulator is the result of the heat source being too high and may result in the canner boiling dry. In addition, it may cause liquid loss in your jars of food. It is essential to understand what a slow, steady rocking motion looks and sounds like. Click the video link for reference.

Question 157. Is it better to overprocess food than underprocess?

It is better to overprocess. Underprocessing may result in spoilage and unsafe food.

Question 78. During processing the pressure dropped below the recommended amount. Is that 
a problem?

Yes. If the pressure drops, it needs to be restored to the recommended level, and the processing time must start from the beginning.


 

FOOD SPECIFIC QUESTIONS

Question 151. What causes beets to lose their color during processing?

It is not unusual for beets to lose some color vibrancy during processing. The best way to minimize the loss is to precook the beets leaving one inch of the stem and root intact. After cooking, slip off the skins and remove the stem and root. A more noticeable color loss or change in color may be due to the variety of beets used for canning. Two varieties of beets that retain color well are Ruby Queen and Detroit Red. Color loss may also result from water that is alkaline in nature. 

Question 72. What causes corn to turn brown during processing?

Caramelization of the natural sugar in corn causes the brown color. This change can occur when canning super sweet varieties of corn. This color change is not harmful.

Question 153. Is it safe to can fruits without sugar?

Yes. The sugar in syrup does not preserve the fruit, but it does improve flavor, help stabilize color, and retain the shape of the fruit. Fruit which has been canned without sugar will often turn brown when exposed to air just as fresh fruit does. 

Question 74. When canning meat, why is it necessary to remove as much fat as possible before canning?

During processing, any fat that gets on the rim of the canning jar can prevent an airtight seal. Leaving excess fat on meat makes it easier for the fat to climb the sides of the jar and contaminate the seal. 

Question 155. Why can’t I can my own salsa recipe?

There are many factors. Salsas are usually a blend of acid and low-acid ingredients. Tested salsa recipes with a pH less than 4.6 are categorized as high-acid and are appropriately canned using the boiling water method. The specific proportion of ingredients (including tomatoes, peppers, herbs, and other vegetables), preparation procedures, and the final consistency of the salsa are necessary components in determining the acidity level of the mixture. Extensive testing is also required to develop the proper processing time for a safe canned product. If your recipe mixture has less acidity raising the pH value, it would require the pressure canning method, which is not recommended. With all the factors listed above, we must rely on research tested recipes to guarantee safe home canning results.

Question 76. Do I have to peel tomatoes?

Yes. Washing fresh food removes only a slight amount of bacteria, yeast, and mold from the surface of the food. Peeling tomatoes, however, removes the bacteria, yeast, and mold load greatly. Research tested recipes were developed using specific preparation procedures. Changing those procedures, ingredients, or steps may also change the quality and, most importantly, the safety of the finished product.

Question 157. Why do I have to acidify tomatoes?

Tomatoes have a natural pH close to and above 4.6, which means it is necessary to take precautions to can them safely. The USDA recommends a small amount of acid be added to tomatoes so they can be treated as a food with a pH less than 4.6 for home canning using the boiling water method. Penn State developed the equivalent safe pressure canning times for tomatoes with acidification. Therefore, this acidification recommendation for tomatoes applies to both boiling water canning and pressure canning. The pressure canning process developed is not a heat substitute for acidification. It is just a somewhat faster equivalent that still requires acidification. For more information on how to acidify, see Tomatoes Basics.

Question 78. What does “raw pack” and “hot pack” mean when canning tomatoes?

Some tested recipes specify raw pack and some specify hot pack. If both raw and hot pack are listed, you may choose the method you prefer based on the information below. Always follow the pack specified in the research-tested canning recipe.

Raw pack: Unheated tomatoes are put directly into the jars and then covered with boiling water. Tomatoes should be packed loosely because they expand during processing.

Raw pack requires less upfront preparation; however, the tomatoes typically separate during processing into a liquid and solid, with the solids forming on top of the liquid. This change is due to an enzyme that causes tomatoes to break apart when heated. Flavor and nutritional quality are not affected by this change.

Hot pack: Tomatoes are heated to boiling as directed in the recipe before being packed into jars.

Hot pack will require more upfront preparation time heating the tomatoes, but there is less chance of liquid and solid separation.

Question 159. Should I can tomatoes using the pressure canning method or boiling water method?

Many tomatoes and tomato products are safely and acceptably processed using either method. The exceptions are spaghetti sauce and salsa. Spaghetti sauce has a relatively large quantity of low-acid ingredients and therefore requires the pressure canning method. Salsas are more acceptably processed using the boiling water method.

If both methods are listed in a tested recipe, you may choose either method. If only one method is listed in your tested recipe, it is due to the pH value of the recipe ingredients and you must follow the specified method. 

 

Canning Index | Canning Introduction | Frequently Asked Questions | Pressure Canning Method
Boiling Water Method | Fruits | Tomatoes and Tomato Products | Vegetables | Meat, Game and Poultry
Fish and Seafood | Stock and Soup | Troubleshooting | Care and Maintenance| Pressure Canner Comparison Guide