Canning tomatoes is a time-honored tradition, a way to capture the taste of summer and enjoy it year-round. But when it comes to preserving these garden gems, one question always arises: Should you pressure can or water bath tomatoes? The answer isn’t always straightforward and depends on several factors. Understanding the science behind canning, the acidity of your tomatoes, and the recipes you’re using is crucial for ensuring a safe and delicious final product. This comprehensive guide will walk you through everything you need to know to make the right choice.
Understanding the Science of Canning
Canning is all about creating an environment where harmful microorganisms, particularly Clostridium botulinum (the bacteria that causes botulism), cannot survive. These bacteria thrive in low-acid, anaerobic (oxygen-free) environments, like the inside of a sealed jar. To prevent botulism, we need to either eliminate these bacteria or create an environment where they cannot grow.
High-Acid vs. Low-Acid Foods
The level of acidity in food is measured using pH. Foods with a pH of 4.6 or lower are considered high-acid, while those with a pH above 4.6 are considered low-acid. High-acid foods can be safely processed in a boiling water bath canner because the high acidity inhibits the growth of Clostridium botulinum. Low-acid foods, on the other hand, require pressure canning to reach temperatures high enough to kill the bacteria.
Tomatoes, while often perceived as acidic, can actually vary in their pH levels. Most tomatoes fall on the borderline between high and low acidity, making the canning method a critical decision. The variety of tomato, growing conditions, and even ripeness can affect their acidity.
Water Bath Canning Tomatoes: When It’s Safe
Water bath canning involves submerging sealed jars of food in boiling water for a specific amount of time. The boiling water temperature (212°F or 100°C at sea level) is sufficient to kill molds, yeasts, and some bacteria in high-acid foods.
Boosting Acidity for Water Bath Canning
Because of the variability in tomato acidity, it’s crucial to increase the acidity of your tomatoes before water bath canning. This is typically done by adding lemon juice, citric acid, or vinegar to each jar. The recommended amount of lemon juice is usually 1 tablespoon per pint jar or 2 tablespoons per quart jar. For citric acid, use 1/4 teaspoon per pint or 1/2 teaspoon per quart. When using vinegar, always opt for a 5% acidity vinegar and follow tested recipes carefully.
The addition of these acids ensures that the pH of the tomatoes is low enough to safely inhibit the growth of Clostridium botulinum during storage. Always use precise measurements of the acidifying agent. Guessing can be dangerous.
Acceptable Tomato Products for Water Bath Canning
You can safely water bath can certain tomato products when properly acidified. These include:
- Whole or crushed tomatoes
- Tomato juice
- Tomato sauce (when following a tested recipe that specifies acid addition)
Remember, even with acidification, you must strictly adhere to tested recipes from reliable sources like the USDA Complete Guide to Home Canning, university extension services, or reputable canning recipe books.
Pressure Canning Tomatoes: The Sure Bet
Pressure canning uses a special appliance that creates a pressurized environment, allowing the temperature inside the canner to rise above the boiling point of water. This higher temperature (240°F or 116°C) is necessary to kill Clostridium botulinum spores in low-acid foods.
When to Choose Pressure Canning
Pressure canning is the safest option for preserving tomatoes, especially if you are unsure about their acidity or if you are adding low-acid ingredients to your tomato products. If you are making recipes that include vegetables like onions, peppers, or celery, pressure canning is essential because these ingredients lower the overall acidity of the mixture.
Always pressure can tomato salsas, tomato soups (especially those with milk or cream), and any tomato-based recipe that includes significant amounts of low-acid ingredients.
Proper Pressure Canning Techniques
Pressure canning requires meticulous attention to detail. Follow these guidelines for safe and effective pressure canning:
- Use a pressure canner that is in good working order and has been tested for accuracy.
- Follow the manufacturer’s instructions for your specific canner model.
- Adjust the processing time and pressure according to your altitude.
- Vent the canner properly before pressurizing.
- Maintain a steady pressure throughout the processing time.
- Allow the canner to depressurize naturally after processing.
- Carefully inspect the jars for proper sealing.
Never shortcut the processing time or reduce the pressure. Doing so can compromise the safety of your canned goods.
Choosing the Right Method: A Summary
Here’s a breakdown to help you decide which method is appropriate:
- Water Bath Canning: Suitable for plain tomato juice, crushed tomatoes, or whole tomatoes when properly acidified with lemon juice, citric acid, or vinegar, and following a tested recipe.
- Pressure Canning: The safest option for any tomato product, especially those containing low-acid ingredients like onions, peppers, or other vegetables. Essential for salsas and tomato soups.
Factors Affecting Acidity
Several factors can influence the acidity of your tomatoes, impacting your choice of canning method.
- Tomato Variety: Some tomato varieties are naturally more acidic than others. Roma and other paste tomatoes tend to be more acidic than beefsteak or heirloom varieties.
- Ripeness: Overripe tomatoes may have lower acidity levels.
- Growing Conditions: Soil conditions, weather, and the use of fertilizers can all affect tomato acidity.
- Additions to the Jar: Adding anything other than acidifying agents, such as herbs, spices, or water, can dilute the acidity and affect safety.
Safe Canning Practices: Beyond the Basics
Regardless of whether you choose to water bath can or pressure can, always follow these general safe canning practices:
- Use only tested recipes from reputable sources.
- Use only canning jars and lids designed for home canning.
- Inspect jars for cracks or chips before filling.
- Wash jars in hot, soapy water and rinse thoroughly.
- Heat lids in simmering water before applying them to jars.
- Leave the correct headspace in each jar (usually 1/2 inch for tomatoes).
- Remove air bubbles from the jars before sealing.
- Wipe the jar rims clean before applying lids.
- Process jars for the recommended time based on your altitude.
- After processing, let the jars cool completely before checking the seals.
- Label and date your jars.
- Store canned goods in a cool, dark, and dry place.
If a jar does not seal properly, reprocess it immediately or refrigerate and use the contents within a few days. Never eat food from a jar that shows signs of spoilage, such as bulging lids, unusual odors, or mold.
Addressing Common Concerns
Canning can seem intimidating, but with proper knowledge and attention to detail, it’s a safe and rewarding way to preserve your harvest.
Altitude Adjustments
Altitude affects the boiling point of water. At higher altitudes, water boils at a lower temperature, which means you need to increase the processing time for both water bath and pressure canning to ensure that the food reaches a safe temperature. Consult altitude adjustment charts in reputable canning guides for specific recommendations.
Recipe Variations
Never deviate from tested canning recipes. Changing the ingredients or proportions can affect the acidity and safety of the final product. If you want to experiment with flavors, do so after opening the jar and before serving.
Jar Size Considerations
Processing times vary depending on the size of the jar. Follow the processing times specified in the recipe for the specific jar size you are using. Do not assume that you can simply increase or decrease the processing time proportionally for different jar sizes.
In Conclusion: Canning Tomatoes with Confidence
Choosing between pressure canning and water bath canning tomatoes requires careful consideration of the tomato acidity and the ingredients in your recipe. Pressure canning is generally the safer option, especially when dealing with mixed vegetable recipes, salsas, or if you are unsure about the acidity of your tomatoes. Water bath canning is acceptable for plain tomato products like juice, crushed tomatoes, and whole tomatoes, provided they are properly acidified and you follow a tested recipe.
Ultimately, the most important thing is to prioritize safety by following tested recipes from reputable sources and adhering to proper canning techniques. With the right knowledge and equipment, you can enjoy the delicious taste of homegrown tomatoes all year long, knowing that you have preserved them safely.
FAQ 1: What is the main difference between pressure canning and water bath canning for tomatoes?
The core difference lies in the temperature reached during processing. Water bath canning achieves a temperature of 212°F (100°C) at sea level, sufficient for high-acid foods. Pressure canning, on the other hand, reaches temperatures of 240°F (116°C) or higher, necessary to destroy botulism spores in low-acid foods. Tomatoes are borderline in acidity, making the choice between methods crucial for food safety.
Because tomatoes are a low-acid food, using a water bath canner could cause serious illness. In order to safely use a water bath canner, you must acidify the tomatoes. Pressure canning provides a higher level of food safety, regardless of added acids.
FAQ 2: Why is acidity important when canning tomatoes?
Acidity is crucial because it inhibits the growth of Clostridium botulinum, the bacteria that produces the deadly botulism toxin. High-acid environments prevent these spores from germinating and producing the toxin. Foods with a pH of 4.6 or lower are generally safe to process using a water bath canner.
Tomatoes often fall close to this pH level, making them a potential risk. Therefore, acidifying them with lemon juice, citric acid, or vinegar is essential when using a water bath canner to ensure safety. Pressure canning circumvents this issue by reaching temperatures high enough to destroy botulism spores, regardless of the food’s acidity.
FAQ 3: How do I acidify tomatoes for water bath canning?
To properly acidify tomatoes for water bath canning, you need to add a specific amount of acid to each jar. For each quart of tomatoes, add 2 tablespoons of bottled lemon juice or ½ teaspoon of citric acid. For pints, use 1 tablespoon of bottled lemon juice or ¼ teaspoon of citric acid. Always use bottled lemon juice for consistency in acidity.
The acid should be added directly to the jars before filling them with tomatoes. This ensures even distribution of the acid throughout the contents of the jar. It’s crucial to follow these acidification guidelines precisely, as insufficient acid can lead to unsafe canned goods.
FAQ 4: Can I skip the acidification step if I am pressure canning tomatoes?
While pressure canning can destroy botulism spores regardless of acidity, some modern recommendations still suggest adding acid even when pressure canning tomatoes. This is primarily to help preserve the color, texture, and flavor of the tomatoes, as acidity plays a role in these qualities.
The National Center for Home Food Preservation recommends adding ¼ teaspoon of citric acid per pint jar or ½ teaspoon per quart jar, even when pressure canning. It is important to know that acidifying your tomatoes is not a requirement when pressure canning.
FAQ 5: What type of tomatoes are best for canning?
Roma and other paste tomatoes are generally considered the best for canning due to their meaty texture and lower water content. This results in a thicker, richer sauce with less cooking time. They also tend to have fewer seeds, which can affect the quality of the final product.
However, you can successfully can other varieties of tomatoes as well. Just be aware that juicier tomatoes may require a longer cooking time to achieve the desired consistency. Consider removing excess water or pulp before canning if using a more watery tomato variety.
FAQ 6: What are the processing times for pressure canning and water bath canning tomatoes?
Processing times depend on the size of the jar, the density of the contents (whole, crushed, or sauce), and your altitude. Always consult a reputable canning guide, such as the USDA Complete Guide to Home Canning or the National Center for Home Food Preservation, for specific times. For example, crushed tomatoes may require longer processing times than whole tomatoes.
Generally, pressure canning times are shorter than water bath canning times. Water bath canning for pints typically requires 85 minutes at 0-1,000 feet above sea level. Times are longer for higher altitudes. Be sure to adjust processing times based on altitude.
FAQ 7: What are some signs that canned tomatoes have spoiled?
Several signs indicate spoilage in canned tomatoes, making them unsafe to consume. Bulging lids or lids that are not tightly sealed are major red flags. Also, listen for a hissing sound upon opening the jar, which suggests gas production from bacterial activity.
Other warning signs include discoloration, mold growth, an off-putting odor, or a cloudy appearance of the liquid inside the jar. If you observe any of these signs, discard the tomatoes immediately without tasting them. “When in doubt, throw it out” is the golden rule for safe canning.