Properly managed heat sterilization has a great deal to do with the quality of canned food. If the temperature is too high or the time of sterilization too long, the result is a product with poor color, soft texture, and less flavor. Tomatoes canned in the pressure canner are an example.
After heat sterilization, a quality canned food will have liquid covering the solid food in the jar. The lid must allow air, but not liquid, to escape during heat sterilization. A low liquid level in the jar may indicate the lid did not function properly, pressure was allowed to fluctuate in the pressure canner, or the canner wasn’t cooled completely before opening, or raw pack was used. Foods not covered with liquid will have poorer quality.
Jars must be air-cooled naturally after heat sterilization to maintain quality as well as for safety. Delayed cooling in tightly enclosed areas, such as cardboard cartons, will decrease quality of the product.
Storage conditions are vital to quality of canned foods. If stored in a light, rather than a dark place, light-sensitive colors will darken gradually. Some colors, such as carotenoids in tomatoes and carrots will gradually fade with prolonged storage.
Storage temperatures between 40 to 50° F (4.5° to 10° C), if the spot is dry, are best for quality retention. Quality losses are increased when canned foods are stored at higher temperatures. For example, about a third of the vitamin C is lost if foods are stored a year at temperatures of 80° F (26° C) or higher.
Storage temperatures between 50° to 70° F (10° to 21° C) are acceptable.
Properly canned and stored foods should be safe to eat for more than two years. However, for top quality, it is best to can only the amount to be used in one year.
Top quality home canned foods have rich, jewel-like colors, characteristic of the food canned. Colors are those of well-prepared foods ready to be served, rather than fresh uncooked foods or over-cooked foods. Light-colored foods should retain their color with no signs of darkening at tops of jars. Fruits should look neither under-ripe and hard, nor over-ripe and mushy. Vegetables ought to look young and tender, rather than old and starchy. Vegetables and fruits should be free of stems, cores, seeds, or pieces of skin, and be of uniform size, shape and color.