FREQUENTLY ASKED QUESTIONS   CANNING BASICS

CANNING 101 QUESTIONS

1. 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, using 3 quarts of water as directed. 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.

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.

5. 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.

7. 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.

9. 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

1. 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.

3. Can I mix regular mouth jars and wide mouth jars when canning?

Jars of the same size in wide mouth and regular mouth can be combined when processing. However, do not force jars to fit, as jar breakage may occur. Be aware that the maximum capacity stated in your instruction manual may be different than what you achieve when mixing jars.

5. 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.

7. Is there a minimum jar capacity?

There has been considerable discussion regarding minimum capacity, especially with the digital canner. As of 2022, we have determined that no minimum jar capacity is required when processing in the Presto Precise® Digital Canner. However, when pressure canning, Presto® stovetop canners have a minimum jar capacity of 2 quarts or the equivalent if using smaller jars. This is to maintain enough mass in the canner for an adequate cool down period. The Presto Precise Digital Canner cool down is slower than stovetop canners, so there is no need for a minimum capacity.

9. 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?

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.

11. 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

1. 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. 

3. 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. 

5. 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.

7. 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.

9. 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.