Canned tomatoes preserve the bounty of summer.
Canned tomatoes play a role in many recipes, from spaghetti sauce to soup. Select ripe tomatoes for canning and remove skins, cores and any bruised portions. Some farmer's markets sell boxes of canning tomatoes; these are usually smaller specimens not pretty enough for salads or sandwiches, but perfect for cutting up and canning. You can preserve tomatoes by canning them with either a water bath or a pressure canner.
Principles of Canning
Canning preserves food by heating it to a temperature that kills bacteria, molds, yeast and other organisms that can cause the food to spoil. Canning stops enzymes that further ripen the food and creates a vacuum in which new harmful organisms can't grow. Properly canned foods will keep for a year or more when stored in a cool, dry place. Cleanliness is very important in canning to ensure that you don't introduce new organisms into the food. Sterilize all jars, lids and equipment used in the canning process.
Water Bath Method
Water bath canning heats canned foods by boiling them in a large kettle with a lid. The water surrounds the jars, heating the food within. Water bath canning heats the food in the jars to approximately 212 degrees, or the boiling point of water. This is sufficient to kill bacteria in fruits and vegetables that contain a lot of acid, such as tomatoes and pickles. Most canned tomato recipes call for adding a teaspoon or so of lemon juice or vinegar to the tomatoes to increase their acid content and ensure that they are safe for consumption.
Pressure Canner
A pressure canner heats water in a tightly sealed pot. The building steam in the pot creates pressure, raising the temperature past the boiling point of water. These higher temperatures are necessary to kill botulism toxin. A toxin that lives in the ground, botulism toxin is killed by the acid in vinegar, lemon juice and tomatoes, but can live in other, less acidic vegetables. If you ingest any botulism toxin, you could die. While a pressure canner isn't necessary for canning tomatoes, some people prefer this method as an extra method of safety. If you can tomatoes in mixtures with other vegetables or meats, you should always use a pressure canner, since the addition of other ingredients lowers the acidity of the recipe.
Choosing Your Method
If you only want to can tomatoes and don't own a pressure canner, you can use a water bath canner. Add a little lemon juice to your tomatoes to ensure that the acid level is high enough to inhibit botulism. Water bath canners use more water than pressure canners, since the water in the water bath canner must cover the jar, while you only need 2 to 3 in. of water in the bottom of the pressure canner. Pressure canners, however, are usually very heavy, and expensive to purchase.
Tags: botulism toxin, ensure that, lemon juice, pressure canner, bath canner, bath canning
