The vibrant flavors of summer tomatoes are a treasure, and preserving them through canning allows you to enjoy that taste year-round. But can you just grab any tomato from the garden or grocery store and transform it into jars of homemade goodness? The answer, while seemingly simple, is nuanced and requires a closer look at tomato varieties and their characteristics. Not all tomatoes are created equal when it comes to canning.
Understanding Tomato Acidity and Safety
Acidity is the cornerstone of safe home canning. Tomatoes naturally possess acidity, but the level varies significantly between different types. This acidity is crucial because it inhibits the growth of Clostridium botulinum, the bacteria that causes botulism, a potentially fatal form of food poisoning. In low-acid environments, these bacteria can thrive and produce toxins.
The United States Department of Agriculture (USDA) provides guidelines for safe home canning, emphasizing the importance of acidity. They recommend that tomatoes have a pH of 4.6 or lower to be safely canned using a boiling water bath method. Tomatoes with a higher pH (lower acidity) require pressure canning, which reaches higher temperatures that can kill botulism spores.
Measuring Tomato Acidity
While you can’t accurately measure the pH of your tomatoes at home without specialized equipment, it’s essential to understand which varieties are naturally more acidic. Generally, certain types of tomatoes are known to have lower pH values and are therefore considered safer for water bath canning.
The Role of Added Acid
To ensure safety, it’s often recommended to add acid to canned tomatoes, regardless of the variety. This is typically done using bottled lemon juice, citric acid, or vinegar. Adding acid guarantees that the pH is sufficiently low to prevent botulism. The USDA provides specific recommendations for the amount of acid to add per jar size.
Tomato Variety Characteristics and Canning Suitability
Different tomato varieties possess unique characteristics that affect their suitability for canning. Factors like flesh density, water content, and sugar content play a role in the final product’s texture and flavor.
Paste Tomatoes: The Canning Champions
Paste tomatoes, like Roma, San Marzano, and Amish Paste, are often considered the best for canning. These tomatoes have a meaty flesh, low water content, and fewer seeds, making them ideal for creating thick, rich sauces and purees. Their denser texture also holds up well during the canning process, resulting in a less watery final product.
San Marzano tomatoes are particularly prized for their exceptional flavor and are a favorite among home canners. Their elongated shape, firm flesh, and sweet, slightly acidic taste make them perfect for creating authentic Italian sauces.
Slicing Tomatoes: Proceed with Caution
Slicing tomatoes, such as Beefsteak, Brandywine, and Big Boy, are larger and juicier than paste tomatoes. While they can be canned, they require extra precautions. Their higher water content can lead to a thinner sauce, and their lower acidity may necessitate the addition of more acid.
When canning slicing tomatoes, it’s often recommended to remove some of the excess water by simmering the tomatoes for a longer period before canning. This helps to concentrate the flavors and create a thicker consistency.
Cherry and Grape Tomatoes: Not Ideal, but Possible
Cherry and grape tomatoes are small and sweet, but their high water content and small size make them less suitable for canning into sauces or purees. However, they can be pickled or roasted and then canned in oil, offering a unique and flavorful preserve. If you choose to can them whole or halved, always add the recommended amount of acid and follow USDA guidelines carefully.
Heirloom Tomatoes: A Mixed Bag
Heirloom tomatoes are known for their diverse flavors, colors, and shapes. However, their acidity levels can vary widely, making it crucial to research the specific variety before canning. Some heirloom tomatoes are naturally more acidic and can be safely canned with added acid, while others may require pressure canning.
It’s always best to err on the side of caution when canning heirloom tomatoes. Consult reputable sources and consider testing the pH of a batch before processing a large quantity.
Canning Methods: Water Bath vs. Pressure Canning
The method you choose for canning tomatoes depends on their acidity. Water bath canning is suitable for high-acid foods, while pressure canning is necessary for low-acid foods.
Boiling Water Bath Canning
Boiling water bath canning involves submerging jars of food in boiling water for a specific amount of time. The boiling water creates a vacuum seal, preserving the food. This method is safe for tomatoes that have been properly acidified.
Ensure that the jars are fully submerged in the boiling water and that the processing time is adjusted based on your altitude. Altitude affects the boiling point of water, and higher altitudes require longer processing times.
Pressure Canning
Pressure canning uses a specialized pressure canner to create a high-pressure, high-temperature environment. This method is necessary for low-acid foods like meats, vegetables, and some tomato varieties. Pressure canning effectively kills botulism spores.
Follow the manufacturer’s instructions for your pressure canner carefully. Vent the canner properly and maintain the correct pressure throughout the processing time.
Steps for Safe Tomato Canning
Regardless of the tomato variety you choose, following safe canning practices is paramount.
- Select ripe, unblemished tomatoes: Choose tomatoes that are firm, free from bruises, and at their peak ripeness.
- Wash and prepare the tomatoes: Wash the tomatoes thoroughly and remove the cores. You can peel them by blanching them in boiling water for 30-60 seconds and then plunging them into ice water. The skins should slip off easily.
- Prepare the jars and lids: Wash the canning jars in hot, soapy water and rinse them well. Sterilize the jars by boiling them in water for 10 minutes. Heat the lids in hot (not boiling) water to soften the sealing compound.
- Add acid: Add the recommended amount of bottled lemon juice, citric acid, or vinegar to each jar. The USDA provides specific guidelines for the amount of acid to add based on jar size.
- Fill the jars: Pack the tomatoes into the jars, leaving the appropriate headspace (usually ½ inch). Remove any air bubbles by running a non-metallic spatula around the inside of the jar.
- Wipe the jar rims: Wipe the rims of the jars with a clean, damp cloth to ensure a good seal.
- Place the lids and rings: Place the lids on the jars and screw on the rings fingertip tight.
- Process the jars: Process the jars in a boiling water bath or pressure canner according to USDA guidelines. Adjust the processing time based on your altitude.
- Cool and store the jars: Remove the jars from the canner and let them cool completely on a towel-lined surface. As the jars cool, you should hear a popping sound, indicating that a vacuum seal has formed. Check the seals by pressing down on the center of the lid. If the lid doesn’t flex, the jar is sealed. Store the jars in a cool, dark place.
Addressing Common Concerns
Even with careful planning, issues can arise during the canning process. Understanding these potential problems can help you troubleshoot and ensure safe, high-quality canned tomatoes.
Jar Seal Failures
Sometimes, jars fail to seal properly. This can be due to a variety of factors, including improper headspace, damaged jar rims, or insufficient processing time. If a jar doesn’t seal within 24 hours, you can reprocess it with a new lid or refrigerate the contents and use them within a few days.
Liquid Loss During Canning
Some liquid loss during canning is normal, but excessive liquid loss can indicate a problem. This can be caused by overpacking the jars, insufficient headspace, or fluctuating temperatures during processing. To minimize liquid loss, ensure proper headspace, avoid overpacking, and maintain a consistent temperature.
Changes in Color and Texture
Canned tomatoes may experience some changes in color and texture. The tomatoes may become slightly softer and the color may fade slightly. These changes are normal and don’t necessarily indicate spoilage. However, if the tomatoes develop an unusual odor or appearance, discard them.
Conclusion: Canning with Confidence
While the question “Can any type of tomato be canned?” has a complex answer, the key takeaway is understanding acidity and following safe canning practices. By choosing appropriate tomato varieties, adding acid when necessary, and adhering to USDA guidelines, you can confidently preserve your harvest and enjoy the taste of summer tomatoes all year long. Always prioritize safety and consult reputable sources for the most up-to-date information on home canning. Whether you’re using paste tomatoes for a rich sauce or experimenting with heirloom varieties, the satisfaction of creating homemade canned tomatoes is well worth the effort.
Can I can any tomato variety safely, or are some better than others?
While technically you can attempt to can most tomato varieties, some are significantly better and safer for canning than others. The key factor is acidity. Tomatoes naturally have a pH that borders on being low-acid, making them susceptible to botulism if not canned properly. Lower-acid varieties, like some heirlooms and yellow tomatoes, are particularly risky and require added acid, such as lemon juice, citric acid, or vinegar, to ensure safety during the canning process.
Ideal canning tomatoes are those with higher acidity and a meaty texture. Roma and San Marzano tomatoes are popular choices due to their naturally higher acid content and lower water content, which contributes to a thicker sauce. These varieties tend to hold their shape better during canning and provide a more concentrated flavor. Always follow tested and approved canning recipes, regardless of the tomato variety you choose, and adjust the acidity levels as recommended, especially if using less acidic tomatoes.
What happens if I don’t add enough acid when canning low-acid tomatoes?
Insufficient acidity in canned tomatoes creates a dangerous environment for Clostridium botulinum, the bacteria that produces botulism toxin. This bacteria thrives in low-oxygen, low-acid conditions, which is exactly what canned goods provide if not properly processed. Botulism is a severe paralytic illness that can be fatal. Symptoms can appear anywhere from hours to days after consuming contaminated food.
Therefore, adding the correct amount of acid is non-negotiable when canning tomatoes, particularly low-acid varieties. Approved canning recipes provide specific instructions for adding acid, based on the type of tomato and canning method. Always measure the acid precisely, using a reliable measuring tool. Err on the side of caution and add the recommended amount, even if your tomatoes seem naturally acidic. This ensures the safety and longevity of your canned goods.
Is it safe to can tomatoes using the open-kettle method?
No, the open-kettle method of canning is not considered safe for tomatoes or any other food. This outdated method involves cooking food in a pot, spooning it into sterilized jars, and then sealing the jars without any further heat processing. While it might seem convenient, it doesn’t generate enough heat to eliminate harmful microorganisms, including Clostridium botulinum spores, that can survive in the jars.
Modern canning methods, such as water bath canning and pressure canning, provide a consistent and controlled heat process that effectively destroys harmful bacteria and creates a vacuum seal, preventing spoilage. These methods are thoroughly tested and scientifically proven to ensure the safety and long-term preservation of canned goods. Always use approved canning methods and recipes from reputable sources like the USDA or your local extension office.
Can I reuse old canning jars and lids?
Canning jars can be reused indefinitely, as long as they are free from chips, cracks, and other damage. Inspect each jar carefully before each use. Nicks or imperfections in the rim of the jar can prevent a proper seal, leading to spoilage. Wash and sterilize the jars thoroughly before filling them with your tomato mixture.
However, lids cannot be reused for canning. The sealing compound on the underside of the lid is designed for a single use. Once it has been used and heated, it may not create a proper seal on subsequent uses. Reusing lids can lead to seal failure, spoilage, and potentially dangerous foodborne illnesses. Always use new, unused lids for each batch of canned tomatoes.
Do I need to peel tomatoes before canning them?
Whether or not to peel tomatoes before canning is a matter of preference, but it is generally recommended. Tomato skins can become tough and bitter during the canning process and may separate from the tomato flesh, creating an undesirable texture in the final product. Peeling tomatoes is a simple process that can significantly improve the quality of your canned goods.
The easiest way to peel tomatoes is to blanch them briefly in boiling water. Score the bottom of each tomato with an “X,” then immerse them in boiling water for 30-60 seconds, or until the skins begin to loosen. Immediately transfer the tomatoes to an ice bath to stop the cooking process. The skins should then slip off easily with your fingers. Leaving skins on is not unsafe, but it can affect the texture and appearance of your canned tomatoes.
What’s the difference between water bath canning and pressure canning tomatoes?
The primary difference between water bath canning and pressure canning lies in the temperature reached inside the jars during processing. Water bath canning uses boiling water (212°F or 100°C at sea level), which is sufficient for high-acid foods like jams, jellies, and properly acidified tomatoes. The high acidity prevents the growth of Clostridium botulinum spores.
Pressure canning, on the other hand, uses steam under pressure to achieve higher temperatures (typically 240°F or 116°C), which are necessary to destroy Clostridium botulinum spores in low-acid foods. While properly acidified tomatoes can be safely processed in a water bath canner, some recipes may recommend pressure canning for larger jars or specific tomato products, depending on the recipe and the added ingredients.
How long will properly canned tomatoes last?
Properly canned tomatoes, processed using approved methods and stored in a cool, dark, and dry place, can last for at least one year and often longer. The ideal storage temperature is between 50°F and 70°F (10°C and 21°C). Avoid storing canned goods in areas subject to extreme temperature fluctuations, such as near a furnace or in direct sunlight.
While the tomatoes may remain safe to eat for several years, the quality (flavor, texture, and color) may gradually decline over time. It’s best to use canned tomatoes within 12-18 months for optimal quality. Always check the seal of each jar before opening. If the lid is bulging or the contents appear discolored or have an unusual odor, discard the jar without tasting it. Botulism toxin is odorless and tasteless.