How to can

What is Canning?

Canning is a widely used method for preserving food that involves sealing food in airtight containers, typically glass jars, and then heating them to a specific temperature for a set amount of time. This heat treatment serves two primary purposes: it destroys microorganisms like bacteria, yeasts, and molds that cause spoilage, and it inactivates enzymes that can lead to food degradation. As the sealed containers cool, a vacuum is formed, which helps to keep the contents preserved and prevents recontamination.

Why Can Food?

The primary advantage of canning is extending the shelf life of food significantly. It allows consumers to enjoy seasonal produce year-round, preserve harvests from gardens, and have a readily available supply of food in case of emergencies or shortages. Properly canned foods can retain their nutritional value and quality for extended periods, often several years, when stored correctly. It also offers a way to reduce food waste by preserving surplus ingredients.

Types of Canning Methods

There are two main methods of home canning, distinguished by the types of food they are suitable for and the equipment required:

Boiling Water Bath Canning

This method is suitable for high-acid foods, which include most fruits, jams, jellies, and pickled vegetables. The process involves submerging filled jars in boiling water (212°F or 100°C at sea level) for a specified processing time. The high acidity of these foods helps to inhibit the growth of harmful bacteria, including the spores that cause botulism. Boiling water bath canners are typically large pots with racks to keep jars from touching the bottom and a lid.

Pressure Canning

This method is essential for preserving low-acid foods, such as vegetables, meats, poultry, and seafood. Low-acid foods do not have enough acidity to prevent the growth of Clostridium botulinum, a bacterium that produces a deadly toxin. Pressure canning uses a specialized canner that operates under pressure, allowing the internal temperature to reach levels significantly higher than boiling (typically 240-250°F or 116-121°C). These higher temperatures are necessary to destroy botulism spores. Pressure canners are more complex than water bath canners, featuring a pressure gauge or regulator and a locking mechanism.

Essential Canning Equipment

Successful canning relies on using the correct equipment:

• Canning Jars: Specially designed Mason jars made of tempered glass are required. Regular glass jars are not suitable as they may break under the heat and pressure.
• Lids and Bands: Canning lids consist of a flat metal disc with a sealing compound and a screw band. Only new lids should be used for each canning session, as the sealing compound can degrade over time. Bands are reusable.
• Canner: Either a boiling water bath canner or a pressure canner, depending on the food being preserved.
• Jar Lifter: A tool used to safely lift hot jars in and out of the canner.
• Funnel: A wide-mouth funnel helps fill jars without spilling.
• Bubble Remover/Headspace Tool: Used to remove air bubbles from the jars and ensure the correct headspace (the space between the food and the top of the jar).

The Canning Process: Step-by-Step

While specific instructions vary by recipe and food type, the general steps for canning are:

1. Prepare Jars and Lids: Jars should be washed and sterilized. Lids are typically kept warm according to manufacturer instructions.
2. Prepare Food: Follow a tested recipe for the specific food you are canning. This includes washing, chopping, and cooking the food as directed.
3. Fill Jars: Pack food into the jars, leaving the recommended headspace. Remove air bubbles and adjust headspace if necessary. Wipe jar rims clean.
4. Apply Lids and Bands: Center the lid on the jar and screw on the band fingertip tight.
5. Process Jars: Place jars in the canner according to the method (boiling water bath or pressure). Process for the time specified in the tested recipe, adjusting for altitude if necessary.
6. Cool Jars: Remove jars from the canner and let them cool undisturbed for 12-24 hours. You should hear a "ping" sound as the lids seal.
7. Check Seals: Once cooled, remove the bands and check the seals by pressing the center of the lid. If it doesn't flex, the jar is sealed. Store sealed jars without the bands.

Safety Considerations

Canning requires strict adherence to safety guidelines to prevent foodborne illnesses. The most significant risk is botulism, which can occur when low-acid foods are improperly canned. Always use up-to-date, scientifically tested recipes from reliable sources like university extension offices or the National Center for Home Food Preservation. Never taste food from a jar with a bulging lid or a seal that has broken, as it may contain botulinum toxin. If in doubt, throw it out.

Storage of Canned Goods

Proper storage is crucial for maintaining the quality and safety of canned foods. Store jars in a cool (ideally 50-70°F or 10-21°C), dark, dry place. Avoid extreme temperature fluctuations. Canned foods are best used within one year for optimal quality, although they remain safe to eat for much longer if properly sealed and stored. Inspect jars before opening for any signs of spoilage, such as bulging lids, leaks, or off-odors.