How to Can Tomatoes with a Pressure Cooker?
Pressure canning tomatoes allows for safe and efficient preservation of low-acid tomato varieties and tomato products. By using a pressure cooker at the correct PSI and processing time, you can eliminate the risk of botulism and ensure your canned tomatoes are shelf-stable for long-term storage.
Introduction: The Art and Science of Home Canning Tomatoes
Home canning is a time-honored tradition, offering a way to savor the bounty of the season year-round. Tomatoes, a staple in many kitchens, are a popular choice for canning. While water bath canning works well for high-acid tomatoes and tomato products with added acid, a pressure cooker is essential for safely preserving low-acid tomatoes or mixes without acidification. This method utilizes high heat under pressure to eliminate harmful bacteria, ensuring the safety and quality of your canned goods.
Why Pressure Canning Tomatoes is Crucial
The primary concern when canning any food is the potential for Clostridium botulinum bacteria to thrive. This bacterium produces a deadly toxin, botulinum toxin, which causes botulism, a serious illness. Low-acid foods like many tomato varieties (especially paste tomatoes), beans, and meats provide an ideal environment for this bacteria to grow.
- Water bath canning, reaching a temperature of 212°F (100°C), isn’t hot enough to kill Clostridium botulinum spores in low-acid foods.
- Pressure canning, achieving temperatures of 240°F (116°C) or higher, is the only safe method for canning low-acid foods at home.
Even adding acid to tomatoes isn’t a foolproof guarantee against botulism. Using a pressure canner ensures safety, especially for mixed tomato products.
Understanding Your Pressure Canner
Before you begin, it’s crucial to understand the type of pressure canner you have:
- Dial Gauge Canner: These have a gauge that shows the pressure inside the canner. They require periodic testing for accuracy.
- Weighted Gauge Canner: These use weighted regulators that jiggle to release excess pressure. They are simpler to use and don’t require calibration.
Regardless of the type, always follow the manufacturer’s instructions specific to your model.
Supplies You’ll Need
Gathering your supplies before starting streamlines the process. Here’s a checklist:
- Pressure canner with rack
- Canning jars (pint or quart, with new lids and rings)
- Jar lifter
- Lid wand (magnetic)
- Wide-mouth funnel
- Clean kitchen towels
- Timer
- Measuring cups and spoons
- Large pot for blanching tomatoes
- Slotted spoon or skimmer
- Knife for scoring tomatoes
Choosing and Preparing Tomatoes
The quality of your tomatoes directly impacts the quality of your canned product.
- Select ripe, unblemished tomatoes.
- Wash tomatoes thoroughly.
- Core tomatoes and score an ‘X’ on the blossom end. This helps with peeling.
Step-by-Step Pressure Canning Process
Here’s a detailed guide to pressure canning tomatoes:
- Prepare Jars: Wash jars, lids, and rings in hot, soapy water. Keep jars hot until ready to fill by simmering them in a pot of water. Sterilizing the jars is only necessary if processing for less than 10 minutes.
- Blanch and Peel Tomatoes: Immerse tomatoes in boiling water for 30-60 seconds until the skins crack. Transfer to an ice bath to stop cooking. Peel the skins off.
- Prepare Tomatoes: You can leave tomatoes whole, quarter them, crush them, or make sauce. Follow a tested recipe for the specific preparation you choose. Add bottled lemon juice or citric acid based on recipe requirements. This is essential if you are unsure about the acidity of your tomatoes, or if you are canning a recipe with added low acid ingredients like peppers or onions.
- Fill Jars: Using a wide-mouth funnel, fill the jars with the prepared tomatoes, leaving the appropriate headspace (usually ½ inch).
- Remove Air Bubbles: Run a non-metallic utensil (e.g., spatula) around the inside of the jar to release any trapped air bubbles.
- Wipe Jar Rims: Clean the jar rims with a clean, damp cloth to ensure a good seal.
- Place Lids and Rings: Center a lid on each jar and screw on a ring until fingertip tight (not too tight, not too loose).
- Load Canner: Place the jar rack in the pressure canner. Add the amount of water specified in your canner’s instructions (usually 2-3 inches). Load the filled jars into the canner, ensuring they don’t touch each other.
- Seal Canner: Secure the canner lid according to the manufacturer’s instructions.
- Vent Canner: Turn the heat to high and allow the canner to vent steam for 10 minutes.
- Pressurize Canner: Close the vent (or place the weight on the vent) and allow the pressure to build to the recommended PSI for your altitude and the type of tomato product you are canning.
- Process Jars: Once the correct pressure is reached, begin timing. Maintain the pressure consistently throughout the processing time. Adjust the heat as needed.
- Cool Canner: Once the processing time is complete, turn off the heat and allow the canner to cool naturally until the pressure returns to zero. Do not force cool the canner.
- Remove Lids Carefully: Carefully remove the weight from a weighted gauge or open the vent on a dial gauge. Be careful to angle your face away from the steam.
- Remove Jars: Using a jar lifter, carefully remove the jars from the canner and place them on a towel-lined surface, leaving at least one inch of space between them.
- Check Seals: Let the jars cool completely for 12-24 hours. After cooling, check the seals. The lids should be concave and not flex when pressed.
- Store Jars: Remove the rings, wash the jars, label and date them, and store them in a cool, dark place. Jars that didn’t seal properly should be refrigerated and used within a week, or frozen for longer storage.
Troubleshooting: Common Mistakes and Solutions
| Mistake | Solution |
|---|---|
| Incorrect Headspace | Adjust headspace before processing. Too little can cause jars to burst; too much can lead to seal failure. |
| Inconsistent Pressure | Monitor the pressure closely and adjust the heat as needed to maintain a consistent PSI. |
| Insufficient Processing Time | Always follow recommended processing times for your altitude and the type of tomato product. Underprocessing can lead to spoilage. |
| Forcing the Canner to Cool | Allow the canner to cool naturally. Forcing it to cool can cause jars to break or the food to spoil. |
| Reusing Old Lids | Always use new lids for canning. Old lids may not seal properly. |
| Adding too little acid | Make sure to add enough citric acid or lemon juice for low-acid tomatoes or for tomato mixtures that include low acid ingredients like peppers and onions. |
Frequently Asked Questions (FAQs)
What kind of pressure canner should I use?
Both dial gauge and weighted gauge pressure canners are suitable for canning tomatoes. Dial gauge canners require more frequent testing for accuracy, while weighted gauge canners are simpler to use and maintain. Choose the type that best suits your needs and comfort level.
Do I really need to add acid to tomatoes before canning?
Yes, adding acid is crucial, especially if you are unsure about the acidity of your tomatoes or if you’re canning a tomato mixture that includes lower acid vegetables like peppers or onions. This ensures a safe pH level to prevent botulism.
What is headspace, and why is it important?
Headspace is the space between the top of the food and the lid of the jar. Proper headspace is essential for creating a vacuum seal. Too little headspace can cause food to seep out during processing, while too much can prevent a proper seal.
How do I adjust processing times for my altitude?
Altitude affects the boiling point of water, so you need to adjust processing times or pressure for higher altitudes. Refer to your canner’s manual or a reputable canning resource for specific guidelines. Increase both processing time and pressure when at higher altitudes.
What if a jar doesn’t seal properly after processing?
If a jar doesn’t seal, refrigerate it immediately and use the contents within a week. Alternatively, you can freeze the contents for longer storage. Do not reprocess a jar that didn’t seal after its initial processing time.
Can I use different sized jars than the recipe specifies?
It’s generally not recommended to use different sized jars than the recipe specifies. The processing times are calibrated for specific jar sizes, and using different sizes can lead to under-processing or over-processing.
How long can I store home-canned tomatoes?
Properly canned tomatoes can be stored in a cool, dark place for at least one year, and sometimes longer. It is always best to consume your canned goods within two years for best quality.
What are the signs of spoilage in canned tomatoes?
Discard any canned tomatoes if you notice signs of spoilage, such as a bulging lid, cloudy liquid, unusual odor, or if the contents spurt out when the jar is opened. Never taste food from a suspect jar.
Can I add other vegetables to my canned tomatoes?
Yes, you can add other vegetables to your canned tomatoes, but always follow a tested recipe. Adding low-acid vegetables will increase the acidity level required, and different ratios of vegetables to tomatoes affect the heat penetration and processing time. Refer to a USDA Complete Guide to Home Canning or your local Extension Office for approved recipes.
What is “venting” the pressure canner?
Venting is the process of allowing steam to escape from the pressure canner for 10 minutes before pressurizing. This removes air from the canner, which can affect the temperature and processing time.
Is it safe to can tomatoes if they are bruised?
It is not recommended to can bruised or damaged tomatoes. Bruised areas can harbor bacteria and affect the quality and safety of the canned product.
Why do my canned tomatoes sometimes separate?
Separation is normal in canned tomatoes. This is because the water separates from the solids. Give the jar a good shake before using the tomatoes. Adding a small amount of calcium chloride (Pickle Crisp) to the jars before processing can help reduce separation.