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Excerpt from the Popular Kitchen Series magabook Canning & Preserving with permission from its publisher, BowTie magazines, a division of BowTie Inc. Purchase Canning & Preserving.

Many problems can arise with canning. Here are a few common canning problems that you might encounter:

• Canning jars that don’t seal. Tiny nicks on the canning jar rim can prevent sealing; so can food residue left on the rim when a jar is filled, food that overflows because of insufficient head space or excess air left by too much head space in the jar. Solutions to this canning problem: If a canning jar doesn’t seal, remove the lid and reprocess the contents within 24 hours. Use a new jar if the old one is nicked, and always use a new canning jar lid.
• Loss of liquid during processing. Liquid can escape from the jars during pressure canning if the pressure fluctuates during processing or suddenly drops when the processing is complete. Air bubbles trapped in a canning jar’s contents also can cause liquid loss. Solutions to this canning problem: To prevent air bubbles, slide a chopstick or non-metallic knife between the canning jar and the food, and press it gently back and forth.
• Food that darkens at the top of the jar. Air bubbles or too much head space can cause food to oxidize and darken. This discoloration generally is not a sign of spoilage if the canning jar is sealed. Solutions to this canning problem: To prevent darkening, use the head space specified in each recipe. Generally, low-acid foods require 1 inch of head space; high-acid foods require ½ inch; jams, jellies, juices and pickles require ¼ inch.
• Undesirable color changes. Chemical reactions resulting from contact with iron, zinc or copper can cause the food to change color. Solutions to this canning problem: To prevent this change in color, select cookware made from nonreactive materials, such as stainless steel and plastic, and make sure your water is soft. Color changes might occur if you can unripe produce and over-process it. Some vegetables, including cauliflower, change color because of harmless natural substances that the vegetables contain.
• Cloudy liquid. Starch in unripe vegetables, additives in salt or minerals in water can cause clouding. Solutions to this canning problem: Use only ripe vegetables, pickling or canning salt (which has no additives), and use soft water when canning. If you did all of the above and still have cloudy liquid, the food might be spoiled because of incorrect processing.
• Floating fruit. Fruit can float to the top of the canning jar if it is lighter than the syrup it is packed in, if air is trapped in the jar or if the jar is packed incorrectly. Solutions to this canning problem: To prevent floating, hot-pack fruit in lighter syrup, pack it a closely as possible without crushing it, release air bubbles by running a plastic knife in the jar, and make sure the fruit is covered with liquid before closing the jars.