How to Canning Food Safely at Home: A Comprehensive Guide

Canning is a fantastic way to preserve food, ensuring you can enjoy the flavors of fresh produce long after the season has passed. When practiced correctly, it’s a safe and reliable method. The core principle involves sealing food in jars and applying heat to eliminate microorganisms that could cause spoilage or pose health risks. This process also deactivates enzymes that can degrade food quality. During heating, air is expelled from the jar, creating a vacuum seal upon cooling. This seal prevents air and new microorganisms from re-entering and contaminating the food.

Proper home canning techniques are crucial for safe and effective food preservation.

To ensure safe home canning and prevent foodborne illnesses, it’s imperative to follow research-based canning methods. Botulism, a severe illness, is most commonly associated with improperly home-canned foods. According to the Centers for Disease Control and Prevention, a significant number of botulism outbreaks have been linked to home-canned goods, often due to deviations from recommended canning procedures, failure to use pressure canners for low-acid foods, ignoring signs of spoilage, or a general lack of knowledge regarding botulism risks.

The Importance of Pressure Canning for Low-Acid Foods

Clostridium botulinum bacteria pose the primary risk in canning low-acid foods, making pressure canning an absolute necessity. While boiling temperatures can kill the bacterial cells, they can form spores that withstand such heat. These spores thrive in low-acid environments, particularly in the absence of air, like canned vegetables and meats. As these spores grow, they produce botulinum toxin, a deadly neurotoxin.

To effectively destroy these spores, canning must be done at temperatures of 240°F or higher for a specific duration. These temperatures exceed the boiling point of water (212°F) and are only achievable with a pressure canner.

Safe Canning Methods Explained

There are three primary safe methods for canning, each suited for different types of food:

• Boiling Water Bath Method
• Atmospheric Steam Canning Method
• Pressure Canning Method

Boiling Water Bath Method

The boiling water bath method is ideal for high-acid foods like fruits, tomatoes, pickles, jams, jellies, and other preserves. This method involves completely submerging jars of food in boiling water (212°F at sea level) to heat them.

High-acid foods (with a pH of 4.6 or less) contain sufficient acid to inhibit the growth of Clostridium botulinum spores and the production of their deadly toxin. These foods are safely canned at boiling temperatures using a boiling water bath. Tomatoes and figs, having pH values close to 4.6, require the addition of lemon juice or citric acid to ensure safe canning using this method.

Atmospheric Steam Canning Method

The atmospheric steam canning method is suitable for naturally acidic or properly acidified foods with a pH less than or equal to 4.6, including most fruits, preserves, and pickled vegetables. It’s crucial to note that this method is NOT appropriate for low-acid foods like vegetables and meats.

Historically, there was insufficient research to fully recommend atmospheric steam canners for safe home canning. However, recent research has provided critical information and practices that must be adhered to for safe food canning using a steam canner as an alternative to a boiling water bath. In steam canners, jars are placed on a rack above a water reservoir. The steam generated from the boiling water provides the necessary thermal treatment. This method offers advantages such as lower water consumption, faster temperature attainment, and reduced energy requirements compared to boiling water bath canning.

Atmospheric steam canning offers a convenient alternative for high-acid foods when proper procedures are followed.

Pressure Canning Method

Pressure canning is the only safe method for canning low-acid foods (those with a pH above 4.6), including vegetables, meats, poultry, and seafood. The risk of botulism necessitates the use of a pressure canner for these foods. This method involves placing jars in a pressure canner with 2 to 3 inches of water and heating them to a minimum temperature of 240°F, achievable only within a pressure canner.

Choosing the Right Recipe for Canning Success

It’s essential to use recipes specifically designed for your chosen canning method and sourced from reputable, research-based sources like the USDA, the National Center for Home Food Preservation, and Extension resources. These recipes should provide detailed instructions, including ingredients, ingredient preparation, and processing times for acidic and properly acidified foods.

If you’re canning at an altitude above 1,000 feet, it’s crucial to adjust processing times. Standard canning recipes are generally designed for altitudes between 0 and 1,000 feet, and adjustments are necessary for higher altitudes.

Preparing for the Canning Process

Before beginning, gather and wash all necessary equipment and containers. Select products at their peak quality, avoiding overripe or damaged items. Process only what you can manage within 2 to 3 hours to maintain freshness.

Thoroughly wash the produce in small batches, lifting the food out of the water each time and rinsing until the water is clear. Avoid soaking, which can leach out flavor and nutrients. Clean raw foods are essential for effective canning. Discard any decayed or damaged items.

Preparing Jars and Lids

Inspect jars for any nicks, cracks, or rough edges, which can compromise the airtight seal and lead to spoilage. Wash all canning jars with soapy water, rinse thoroughly, and keep them hot. This can be achieved in a dishwasher or by placing the jars in the water heating in your canner. Keeping jars hot prevents breakage when filling them with hot product and placing them in the canner.

Jars processed for less than 10 minutes in a boiling water bath canner require sterilization by boiling them for 10 minutes. At altitudes of 1,000 feet or higher, increase the boiling time by one minute for each additional 1,000 feet. Jars processed for 10 minutes or more in a boiling water bath or in a pressure canner will be sterilized during processing.

Always use new two-piece lids and follow the manufacturer’s instructions for preparing them. Some lids require simmering in hot water, while others may need to be boiled for a specific period.

Understanding Packing Methods: Raw Pack vs. Hot Pack

Fruits and vegetables can be packed raw or preheated before being placed into canning jars. Hot packing generally yields better color and flavor, especially for foods processed in a boiling water bath. Regardless of the packing method, ensure sufficient syrup, water, or juice to fill the spaces around the solid food and cover it completely. Insufficient liquid can lead to discoloration and unnatural flavors at the top of the jar. Typically, ½ to 1½ cups of liquid are needed for a quart jar.

Raw Pack

The raw pack method involves placing raw, unheated food directly into jars. Boiling hot water, juice, or syrup is then poured over the food to achieve the proper headspace. Fruits and most vegetables packed raw should be packed tightly because they will shrink during processing. However, foods like corn, lima beans, potatoes, and peas should be packed loosely as they expand during canning.

Hot Pack

The hot pack method involves heating the food to boiling (or cooking it for a specified time) before packing the hot food and boiling hot liquid into jars. Because shrinkage has already occurred, pack the foods loosely enough to allow liquid to surround the food.

Step-by-Step Guide to Boiling Water Bath Canning

Use the boiling water bath method exclusively for high-acid foods such as fruits, tomatoes, and pickles.

1. Fill the canner halfway with hot water and heat.
2. For raw-packed jars, the water should be hot but not boiling. For hot-packed jars, use hot or gently boiling water.
3. Fill one jar at a time, following the packing methods described above. Leave the proper headspace, remove air bubbles, and adjust lids.
4. Allow the appropriate headspace as per the recipe to ensure proper air removal and a tight vacuum seal.
5. Run a bubble freer or plastic utensil around the edges of the jar to release trapped air. Add more liquid if needed to maintain proper headspace.
6. Wipe the rims of the jars with a clean, damp cloth.
7. Screw on the lids, but not too tightly, to allow air to escape during processing.
8. Place filled jars on the rack in the canner. Add boiling water as needed to cover the jars by at least 1 inch. Pour water between jars, not directly onto them. Cover the canner.
9. Once the water reaches a rolling boil, begin timing the process. Maintain a gentle and steady boil.
10. If the water stops boiling, return to a vigorous boil and restart the timing from the beginning.
11. After processing, turn off the heat and remove the lid. Wait 5 minutes before removing the jars.
12. Use a jar lifter to carefully remove the jars and place them right side up on a cooling rack or dry towels. Allow at least 1 inch of space between jars and let them cool untouched for 12 to 24 hours. Avoid drafts or covering the jars. Do not tighten the ring bands or press down on the lids until completely cooled.

Step-by-Step Guide to Atmospheric Steam Canning

This method is suitable for high-acid foods only.

1. Use only research-based recipes; do not use recipes provided by the canner manufacturer unless they are research-tested.
2. Steam canners may be used with approved recipes using ½ pint, pint or quart jars. The total processing time, including altitude adjustments, must be less than 45 minutes.
3. The steam canner must vent air and produce pure steam before timing begins. Use caution due to hot steam.
4. Pure steam must remain at the temperature of boiling water (212°F at sea level) throughout the entire processing time. Monitor the temperature with a thermometer placed in the vent hole, ensuring it doesn’t touch a jar.
5. Preheat jars and fill with hot liquid for raw or hot-pack foods.
6. While pre-heating the steam canner isn’t required, it can help keep jars hot.
7. Allow jars to be canned for the full processing time.
8. After processing, turn off the heat and carefully remove the lid, directing steam away from you. Wait 5 minutes before removing jars.
9. Cool jars on a rack or towel at room temperature, away from drafts, with at least 1 inch of space between them. Allow the jars to cool at room temperature for 12-24 hours without forcing cooling.

Proper venting is crucial for safe atmospheric steam canning.

Step-by-Step Guide to Pressure Canning

This is the only safe method for low-acid foods.

1. Read your canner’s instructions thoroughly. Test dial-gauge canners annually for accuracy.
2. Place 2 to 3 inches of hot water in the canner. It should be hot, but not boiling, when canning raw-packed food and hot or gently boiling for hot-packed foods.
3. Fill jars according to the packing method, allowing proper headspace, removing air bubbles, wiping jar rims, and putting on lids.
4. Place jars on the rack, ensuring steam can circulate. Fasten the lid, leaving the vent open.
5. Heat on high until steam escapes steadily from the vent for 10 minutes to remove air.
6. Close the vent using a weight, valve, or screw. Use the correct pressure for your gauge.
7. For dial-gauge canners, let the pressure rise to 8 pounds quickly, then adjust the burner and let the pressure continue to rise to the correct pressure. Start timing when the correct pressure is reached.
8. For weighted-gauge canners, heat quickly, then adjust until the weight rocks gently or “jiggles” as per instructions. Start timing when this occurs.
9. Maintain a steady pressure, adjusting heat as needed.
10. Loss of pressure requires restarting the entire process from the beginning.
11. When processing is complete, remove the canner from the heat or turn it off.
12. Let the pressure drop to zero naturally (30-45 minutes for standard canners, longer for larger ones). Do not rush the cooling process.
13. Depressurize older canners when the gauge reads zero or the weight shows no resistance. Newer canners have safety locks that drop when depressurized. Open the vent or remove the weight. Wait ten minutes, then open the canner.
14. Unfasten the lid, tilting it away from you to avoid steam. Remove jars with a jar lifter and place them on a cooling rack or dry towels, right side up, with at least 1 inch of space between them.
15. Do not tighten lids. Allow jars to cool untouched for 12 to 24 hours.

Safe Handling After Processing

Testing the Seal

Most two-piece lids will “pop” when sealing. After cooling, the lid should curve downward and not move when pressed. Unsealed jars should be refrigerated and used within 2 to 3 days, reprocessed within 24 hours, or frozen.

If liquid is lost from sealed jars, do not open them to replace it; use these jars first. Discoloration may occur, but if sealed, the food is safe.

Labeling and Storing

Remove screw bands to prevent rusting. Wash and dry them for later use. Wash food residue from the jars, rinse, and label with contents, date, and lot number. Store in a clean, cool, dark, dry place between 50 and 70°F, away from heat sources and direct sunlight. Use canned foods within one year for best quality.

Reprocessing Unsealed Jars

If jars do not seal, reprocess within 24 hours. Check the sealing surface for nicks, change the jar if necessary, add a new treated lid, and reprocess using the same processing time. Use recanned foods first, as they will be softer and have lower nutritional value.

Guarding Against Spoilage

Never taste or use canned foods showing signs of spoilage, such as bulging lids, leaking jars, spurting liquid, off-odors, or mold. Dispose of spoiled canned foods where they cannot be eaten by humans or pets.

Suspect containers of spoiled, low-acid foods must be treated as containing botulinum toxin. Properly discard or detoxify them. Low-acid foods are improperly canned if not processed in a pressure canner, if the canner gauge was inaccurate, if up-to-date processing times were not used, if ingredient proportions were changed, or if processing time and pressure were incorrect for the altitude.

Detoxifying Canned, Low-Acid Foods

Contact with botulinum toxin can be fatal. Wear disposable rubber or heavy plastic gloves and protective clothing.

Step-by-Step Detoxification

1. Place jars on their sides in an 8-quart or larger pot or canner.
2. Wash gloved hands thoroughly.
3. Add enough hot water to completely cover the jars with at least 1 inch above the containers.
4. Cover the pot and heat the water to boiling.
5. Boil for 30 minutes.
6. Cool and discard the containers, lids, and food in the trash or a landfill.

Cleaning Contaminated Surfaces

1. Wear gloves to clean contaminated surfaces and equipment.
2. Use a fresh solution of 1 part unscented, liquid, household, chlorine bleach (5 to 6% sodium hypochlorite) to 5 parts clean water.
3. Spray or wet surfaces with the bleach solution and let stand for 30 minutes. Avoid inhaling bleach or contact with skin.
4. Wipe treated spills with paper towels and place them in a plastic bag before putting them in the trash.
5. Apply the bleach solution again, let stand for 30 minutes, and rinse.
6. Wash all detoxified counters, containers, equipment, and clothing.
7. Discard gloves.

By following these guidelines meticulously, you can ensure that your home canning endeavors are safe, enjoyable, and yield delicious, preserved foods for you and your family to enjoy.

Sources:

1. Reynolds, Susan and Paulette Williams. So Easy to Preserve. Cooperative Extension Service, University of Georgia. Revised 2006 by Elizabeth Andress and Judy Harrison.
2. USDA. 2009 Complete Guide to Home Canning.
3. Blakeslee, K. 2015. How-To Guide To Water Bath Canning and Steam Canning. Available from: https://www.bookstore.ksre.ksu.edu/pubs/mf3241.pdf. Accessed February 22, 2019.
4. Centers for Disease Control and Prevention (CDC). 2018. Protect Yourself from Botulism. Atlanta, GA: Centers for Disease Control and Prevention. Available from: https://www.cdc.gov/botulism/consumer.html. Accessed February 22, 2019.
5. Harris, L.J., and Soule, K.E. 2017. Guidelines for Safe Canning of Acid Foods in a Steam Canner. Available from: https://anrcatalog.ucanr.edu/pdf/8573.pdf. Accessed February 22, 2019.
6. Ingham, B. 2015. Guidelines of Using an Atmospheric Steam Canner for Home Food Preservation. Accessed February 22, 2019.
7. National Center for Home Food Preservation (NCHFP). 2015. Burning Issue: Using Atmospheric Steam Canners. Athens, GA: National Center for Home Food Preservation. Available from: https://nchfp.uga.edu/publications/nchfp/factsheets/steam_canners.html. Accessed February 22, 2019.
8. Willmore, P., Etzel, M., Andress, E., and Ingham, B. 2015. Home Processing of Acid Foods in Atmospheric Steam and Boiling Water Canners. Food Protection Trends. 35(3): 150-160.