Canning diced tomatoes at home is a fantastic way to preserve the fresh flavors of summer and ensure you have a ready supply of this kitchen staple throughout the year. However, safety is paramount when pressure canning. Incorrect processing can lead to spoilage and, more seriously, botulism. This comprehensive guide provides everything you need to know about safely and effectively pressure canning diced tomatoes. We will delve into preparation, timing, techniques, and essential safety precautions.
Understanding the Importance of Pressure Canning Tomatoes
Tomatoes, unlike some fruits, are considered a low-acid food. This means they need to be processed in a pressure canner to reach a temperature high enough to destroy Clostridium botulinum spores, the bacteria that cause botulism. Water bath canning, suitable for high-acid foods like jams and pickles, doesn’t reach a sufficient temperature to ensure safety with tomatoes, especially diced tomatoes which may have slightly varying acidity levels.
Always prioritize safety when canning. Following tested and approved recipes and processing times is crucial.
Why Diced Tomatoes Require Pressure Canning
The reason diced tomatoes specifically require pressure canning lies in their composition and potential for trapped air. The density of diced tomatoes packed into jars makes it harder for heat to penetrate evenly. Furthermore, any air pockets within the diced mixture can insulate the contents, preventing the temperature from reaching the required 240°F (116°C) necessary to eliminate botulism spores.
Using a pressure canner allows for the necessary high temperatures to be achieved safely and consistently throughout the jar, guaranteeing proper preservation.
Preparing Your Tomatoes for Canning
Proper preparation is just as important as the canning process itself. It ensures the quality of your final product and contributes to safe preservation.
Selecting the Right Tomatoes
Choose firm, ripe tomatoes without blemishes or signs of spoilage. Overripe tomatoes can have a lower acidity level, potentially compromising safety. Roma or plum tomatoes are often preferred because they are meatier and contain less juice, resulting in a thicker canned product.
Use only high-quality, ripe tomatoes for canning.
Washing and Preparing the Tomatoes
Thoroughly wash the tomatoes under cool, running water. Remove any dirt or debris. Core the tomatoes by cutting out the stem end with a small knife.
Dicing the Tomatoes
You can dice the tomatoes by hand or use a food processor. If using a food processor, pulse carefully to avoid creating a puree. Aim for uniform pieces of about ½ inch in size. Consistent size ensures even heating during processing.
Acidifying the Tomatoes
Because tomato acidity can vary, especially in modern hybrids, adding acid is a crucial step to ensure safe canning. This is typically done with bottled lemon juice or citric acid.
Acidification is mandatory for safe tomato canning.
For each quart jar, add 4 tablespoons of bottled lemon juice or ½ teaspoon of citric acid. For each pint jar, add 2 tablespoons of bottled lemon juice or ¼ teaspoon of citric acid. Do not substitute other acids, such as vinegar, unless specifically stated in a tested recipe. Bottled lemon juice has a consistent acidity level, unlike fresh lemons.
Packing the Jars
How you pack the jars impacts heat penetration and overall safety. It is essential to follow correct procedures.
Choosing the Right Jars and Lids
Use only canning jars designed for home canning. Inspect the jars for any chips or cracks, especially around the rim. Use new, flat lids each time you can. Old lids may not seal properly. The metal bands can be reused if they are in good condition.
Sterilizing the Jars
While sterilization isn’t always necessary for foods processed for 10 minutes or more in a boiling water bath, it’s generally recommended for pressure canning. Sterilize your jars by boiling them in water for 10 minutes. Keep the jars hot until you are ready to fill them. You can also sterilize the jars in the dishwasher.
Hot Packing vs. Raw Packing
There are two main methods for packing tomatoes into jars: hot pack and raw pack.
- Hot Pack: Heat the diced tomatoes in a large pot until they are simmering before packing them into the jars. This method helps to remove air from the tomatoes and improves the vacuum seal.
- Raw Pack: Pack the raw, diced tomatoes directly into the jars. This method requires slightly longer processing times because the tomatoes haven’t been preheated.
For diced tomatoes, hot packing is generally recommended because it helps to eliminate air and improves the density of the packed jars.
Filling the Jars
Whether you are hot packing or raw packing, ladle the diced tomatoes into the hot, sterilized jars, leaving the correct headspace. Headspace is the space between the top of the food and the lid. For diced tomatoes, the recommended headspace is ½ inch.
Use a non-metallic spatula to remove any air bubbles trapped inside the jars. Adjust the headspace as needed.
Wiping the Rims and Applying Lids and Bands
Wipe the rims of the jars with a clean, damp cloth to remove any food residue. This ensures a proper seal. Place the flat lids on top of the jars, and then screw on the metal bands fingertip tight. Do not overtighten the bands, as this can prevent the jars from venting properly during processing.
Pressure Canning: The Essential Steps
Pressure canning is a precise process that requires careful attention to detail.
Loading the Pressure Canner
Place the jars in the pressure canner on the rack. Make sure the jars do not touch each other or the sides of the canner. Add the amount of water specified in your canner’s instruction manual. Typically, this is about 2-3 inches of water.
Venting the Canner
Secure the lid of the pressure canner and turn the heat to high. Allow the canner to vent steam for 10 minutes before closing the vent or placing the weighted gauge. Venting removes air from the canner, which is essential for achieving the correct temperature.
Processing Time and Pressure
The processing time and pressure depend on the type of canner you are using (weighted gauge or dial gauge) and your altitude.
Always consult a tested canning recipe from a reliable source, such as the USDA Complete Guide to Home Canning or your local extension office.
Here are some general guidelines for processing diced tomatoes in a pressure canner:
- Pint Jars:
- Weighted Gauge Canner: 10 minutes at 10 PSI (0-1000 feet altitude) or 15 PSI (above 1000 feet altitude).
- Dial Gauge Canner: 10 minutes at 11 PSI (0-2000 feet altitude), 12 PSI (2001-4000 feet altitude), 13 PSI (4001-6000 feet altitude), or 14 PSI (6001-8000 feet altitude).
- Quart Jars:
- Weighted Gauge Canner: 25 minutes at 10 PSI (0-1000 feet altitude) or 15 PSI (above 1000 feet altitude).
- Dial Gauge Canner: 25 minutes at 11 PSI (0-2000 feet altitude), 12 PSI (2001-4000 feet altitude), 13 PSI (4001-6000 feet altitude), or 14 PSI (6001-8000 feet altitude).
Altitude adjustments are crucial for safe canning. The higher your altitude, the lower the boiling point of water, and the higher the pressure needed to achieve the necessary temperature.
Maintaining Pressure
Once the canner reaches the required pressure, adjust the heat to maintain a steady pressure throughout the processing time. Monitor the gauge frequently to ensure the pressure does not drop. If the pressure drops below the required level, increase the heat and start the processing time over from the beginning.
Cooling the Canner
After the processing time is complete, turn off the heat and allow the canner to cool naturally. Do not force cool the canner by running cold water over it, as this can cause the jars to break or seal improperly.
Wait until the pressure returns to zero before carefully removing the weight or opening the vent. Then, wait an additional 10 minutes before opening the lid.
Post-Processing and Storage
Proper post-processing and storage are vital for ensuring the long-term quality and safety of your canned tomatoes.
Removing the Jars
Carefully remove the jars from the canner using a jar lifter. Place the jars on a towel-lined surface, leaving space between them. Avoid placing the jars directly on a cold countertop, as this can cause them to crack.
Checking the Seals
Allow the jars to cool completely for 12-24 hours. After they have cooled, check the seals. The lids should be concave (curved downward). You can also test the seal by pressing down on the center of the lid. If the lid flexes or pops up, the jar did not seal properly and should be reprocessed with a new lid or refrigerated and used within a few days.
Labeling and Storing
Label the jars with the date and contents. Store the canned tomatoes in a cool, dark, and dry place. Properly canned tomatoes can be stored for up to one year.
Discard any jars that show signs of spoilage, such as bulging lids, unusual odors, or mold growth.
Troubleshooting Common Canning Problems
Even with careful preparation, problems can sometimes occur during the canning process.
Siphoning
Siphoning, or loss of liquid from the jars during processing, can be caused by several factors, including overfilling the jars, not venting the canner properly, or fluctuating pressure during processing. While some liquid loss is normal, excessive siphoning can result in the food above the liquid line discoloring or spoiling more quickly.
To minimize siphoning, ensure you leave the correct headspace, vent the canner for the recommended time, and maintain a consistent pressure throughout processing.
Jar Breakage
Jar breakage can occur if the jars are cracked or chipped, if they are placed directly on a cold surface after processing, or if the canner is cooled too quickly.
Always inspect your jars for damage before filling them, and avoid rapid temperature changes.
Seal Failures
Seal failures can be caused by damaged lids, food residue on the jar rims, or improper processing. Ensure you use new lids, wipe the rims clean, and follow the recommended processing times and pressures.
By following these detailed instructions and safety guidelines, you can confidently and safely pressure can diced tomatoes at home, enjoying the taste of summer all year round. Remember to always prioritize safety and consult reliable resources for accurate information. Enjoy your home-canned bounty!
Why is pressure canning necessary for diced tomatoes?
Pressure canning is essential for safely preserving diced tomatoes due to their low acidity. Tomatoes, even though we often think of them as acidic, generally fall into a pH range that can support the growth of Clostridium botulinum, the bacteria that produces botulism toxin. This toxin is deadly and can grow in anaerobic environments like sealed jars if not properly processed to kill the bacteria.
Boiling water bath canning is only safe for high-acid foods, like certain fruit jams and pickles. Because diced tomatoes are not naturally acidic enough to reliably inhibit botulism growth during water bath canning, pressure canning, which reaches much higher temperatures, is required to eliminate the botulism spores and ensure a safe and shelf-stable product. Adding acid, like lemon juice or citric acid, is also a critical step, but pressure canning provides the necessary heat to destroy the spores, making it a two-pronged approach to safety.
What size jars are suitable for pressure canning diced tomatoes?
You can safely pressure can diced tomatoes in both pint and quart jars. It is crucial to follow the processing times specifically recommended for each jar size in your pressure canner’s instruction manual or a reputable canning guide like the USDA Complete Guide to Home Canning. Using the incorrect processing time can lead to inadequate heat penetration and potentially unsafe food.
Choosing between pint and quart jars often depends on how you plan to use the tomatoes. Pint jars are ideal for smaller households or single servings in recipes like chili or pasta sauce. Quart jars are better suited for larger families or when you’re preparing bigger batches of dishes, such as soups or stews. Ensure your canner has enough space to accommodate the jars you choose, leaving proper headspace.
How much headspace should I leave when canning diced tomatoes?
When pressure canning diced tomatoes, it is crucial to leave the correct amount of headspace in the jars. Leave ½ inch of headspace between the top of the diced tomatoes and the lid of the jar. This space allows for expansion of the contents during processing and creates a proper vacuum seal as the jars cool.
Insufficient headspace can cause food to boil over during processing, potentially contaminating the sealing surface and leading to seal failure. Excessive headspace can result in insufficient vacuum formation, also compromising the seal. Always measure the headspace carefully using a headspace tool or a clean ruler to ensure the proper amount.
What are the recommended processing times for pressure canning diced tomatoes?
The exact processing times for pressure canning diced tomatoes depend on the type of canner you are using (weighted gauge or dial gauge) and your altitude. For weighted gauge canners, pint jars are typically processed for 20 minutes at 10 pounds pressure (for altitudes up to 1,000 feet) or 15 pounds pressure (for altitudes above 1,000 feet). Quart jars generally require 25 minutes at the same pressure levels.
For dial gauge canners, pint jars are processed for 20 minutes at 11 pounds pressure (for altitudes up to 2,000 feet) or at higher pressures as indicated by altitude adjustments in your canner’s manual. Quart jars require 25 minutes at the same pressure levels. Always consult your canner’s manual or the USDA Complete Guide to Home Canning for precise processing times and pressure adjustments based on your altitude and canner type.
How do I add acidity to diced tomatoes before canning?
Adding acidity to diced tomatoes before canning is essential to ensure safe preservation. You must add either bottled lemon juice or citric acid to each jar before filling with the tomatoes. The recommended amount is 1 tablespoon of bottled lemon juice or ¼ teaspoon of citric acid per pint jar, and 2 tablespoons of bottled lemon juice or ½ teaspoon of citric acid per quart jar.
It is critical to use bottled lemon juice, as its acidity level is consistent, unlike fresh lemons, which can vary in acidity. Add the lemon juice or citric acid directly to the bottom of the clean jars before adding the diced tomatoes. This ensures that the entire contents of the jar reach a safe acidity level during the canning process.
What are some common mistakes to avoid when pressure canning diced tomatoes?
One common mistake is failing to add the required amount of acid (lemon juice or citric acid) to each jar. This is a critical step for safety, and skipping it can lead to the growth of botulism bacteria. Always double-check that you’ve added the correct amount to each jar before sealing.
Another frequent error is improper headspace. Insufficient headspace can cause jars to boil over, preventing a proper seal, while excessive headspace can result in insufficient vacuum. Finally, not adjusting processing times or pressure for altitude is a significant mistake. Processing times are crucial for killing botulism spores, and improper adjustments can compromise the safety of your canned tomatoes.
How do I know if my jars of diced tomatoes have sealed properly after pressure canning?
After the jars have cooled completely (usually 12-24 hours), check the seals by pressing down on the center of the lid. If the lid flexes or moves up and down when you press on it, the jar has not sealed properly. A properly sealed lid should be concave (slightly curved inward) and should not move when pressed.
Also, gently tap the lid with a spoon. A clear, ringing sound indicates a good seal, while a dull or flat sound may suggest a faulty seal. If a jar fails to seal, you can either reprocess it with a new lid within 24 hours or store the tomatoes in the refrigerator and use them within a few days. Never consume food from jars with signs of spoilage, such as bulging lids, off odors, or mold.