Here are some basics to remember about processing tomatoes.
• Picking the right tomato: Choose tomatoes that are ripe but still firm with good color and preferably with unblemished skin. They should feel heavy for their size. Round, uniform tomatoes are easier to process than crinkled varieties.
• Average yield: Three pounds of fresh tomatoes are enough to produce 1 quart of canned tomatoes. A bushel (53 pounds) will yield 15 to 20 quarts of crushed tomatoes or 10 quarts of tomato juice.
• Nutrition: Tomatoes retain most of their vitamins when canned. One cup of raw diced tomatoes has about 32 calories. Tomatoes are high in vitamins A and C as well as antioxidants. In particular, tomatoes are very high in lycopene, which helps repair cell damage and protect the body against cancer.
• How to peel a tomato: The easiest method uses boiling water. First, score the tomato with an “X” opposite the stem end. Immerse the fruit in boiling water for 15 seconds or until the skin begins to crack. Lift out with a slotted spoon, then plunge the tomato into ice water. The skin will then slip right off in your hand.
• Freezing whole: Small tomatoes, up to 2 inches in diameter, may be frozen whole with the skin on. When ready to use, remove the frozen tomato from the freezer and run under warm water. The skin will crack and slip off.
• Acidity: Many modern, heirloom and yellow tomatoes have very low acid. That makes them sweeter, but also creates potential for bacterial growth in processing. For food safety, tomatoes needed to be acidified during canning. It also preserves their color. Add 1 tablespoon bottled (not fresh) lemon juice per pint. Bottled lemon juice is used because its acidity is consistent. Citric acid, available in supermarket baking sections, can be used instead. Use 1/4 teaspoon per pint, 1/2 teaspoon per quart.
• No aluminum: Because the acidity in tomatoes reacts with aluminum, use stainless steel or enamel cookware when working with tomatoes.
• How long to process: Canned tomatoes are usually processed in a hot-water bath, which means the jars are boiled with the food inside. (That creates a vacuum that “seals” the jar and keeps bacteria out.) But the processing time varies, depending on several factors. Were the tomatoes packed into the jars raw or hot? Were the jars topped off with water or tomato juice? Tomatoes raw-packed with juice take 85 minutes for pints or quarts to process in a hot-water bath. Hot-packed crushed tomatoes with no added liquid take 35 minutes to process.
• To raw pack: Sterilize jars. In the bottom of each jar, put bottled lemon juice (1 tablespoon for pint jars, 2 tablespoons for quarts). Then add tomatoes. They can be crushed, diced or whole. If packing whole, squeeze the peeled tomatoes into the jar. Use a non-metal spoon or wooden chopstick to squeeze out air bubbles. Add more juice from the tomatoes or water to cover the fruit and fill the jars, leaving 1/2-inch head space.
• To hot pack: Use a large kettle on medium heat. Start with a few tomatoes and keep adding more fruit as the pot heats up. Once all the tomatoes are in the pot, bring to a boil for 5 minutes. Then fill the clean jars, leaving 1/2-inch head space (room for the tomatoes to expand during processing).
• Tomato juice: Wash and core 6 pounds very ripe tomatoes (no need to peel). Simmer in a large kettle for 20 minutes until very soft. Put through a food mill or sieve. Let stand in a bowl until the light watery liquid rises to the top; discard that top layer and save the rest. Makes about 1 quart juice. May be frozen for later use.
• www.pickyourown.org: Besides offering locations of pick-your-own tomato farms, this website has a wealth of tomato recipes and tips.
• Master Food Preservers: Part of the UC Cooperative Extension, these local experts are here to help and answer questions. Go to cesacramento.ucdavis.edu or call (916) 875-6913. Master food preservers have a free 15-page guide to preserving tomatoes at http://anrcatalog.ucdavis.edu.
• National Center for Home Food Preservation: Based at the University of Georgia, this center sets the standards, backed by the USDA. Find many recipes and tips at http://nchfp.uga.edu/.
• Ball brand: With more than 125 years of experience, the Ball brand canning experts have put many recipes and tips online at www.freshpreserving.com.