Removal of skins from thin-skinned foods such as tomatoes and peaches is important. A short blanching time in boiling water loosens the skins, and a short cooling time in cold or ice water stops the cooking of the food. Because water leaches out vitamins, dilutes color and flavor, and results in a mushy product, do not allow foods to soak unnecessarily in either hot or cold water.

Air is an enemy of light-colored foods, and should be kept from the peeled or cut food. This can be done with a commercial antioxidant (ascorbic acid), lemon juice, or a simple solution of two tablespoons each of vinegar and salt per gallon of water. Peel or cut food directly into such a solution for maximum protection from air. When enough food for a canner load is prepared, drain and rinse the food for best flavor.

The packing method used is one of the most important factors in quality canned products. Foods that are heated before being put in jars have better quality than foods packed raw in jars. Heating destroys enzymes and removes much of the air from food tissues.

Enzymes must be destroyed quickly for top-quality food. Removal of air not only shrinks the food, but leads to better color, flavor and nutrient retention, and too, fruits are less likely to float. Hot packed jars also have higher vacuums, thus less oxidation can take place.

Tomatoes and tomato juice are less likely to separate if tomatoes are cut and heated at once. Cutting activates enzymes in tomatoes which then change the pectins in the tomatoes and causes separation. Heating right after cutting inactivates the enzymes and minimizes separation.

Sugar, salt and vinegar play important roles in quality canned foods. While sugar is not needed to safely can fruits, it contributes to better color, flavor and texture. Likewise, vegetables may be safely canned without salt, but when salt is used, better flavor results. Salt is essential for slow process pickles; vinegar is needed for quick process pickles. Canning or pickling salt should always be used. Iodized salt will inhibit proper fermentation and react with the starch in some foods, causing them to turn pink or blue.

Sugar concentration in sirups is important to appearance of the fruit. With a light sirup, fruits are less likely to float than with a heavier sirup. And with a light sirup, fewer calories are added. Then too, the cost is less than with a medium or heavy sirup.

Headspace

Using the proper amount of headspace pays off in quality products. Adequate headspace is needed so food has enough room for expansion during heat sterilization.

Generally, more headspace is needed for foods heat-sterilized in a pressure canner than those in a boiling water canner, because of increased expansion of foods at the higher temperature.

With too little headspace, liquid is more likely to cook out of the jars during heat sterilization. This increases the danger of seal failure due to food particles that may be trapped at the interface of the sealing surface. With too much headspace, air remaining in the jar can cause darkening of the food, oxidized flavor, and lower vitamin retention, especially in food at the top of the jar.

Pressure canning low-acid foods is receiving increased emphasis today, mainly based on the greater safety of this technique. The method also offers an additional advantage that is little known to home canners—improved quality and nutrient retention.

Generally an 18° F (10° C) rise in canner temperatures increases the destruction of bacteria tenfold. At the same time, chemical changes that affect color, flavor, texture and nutrients of the food are only doubled.

This means that for every 18° F (10° C) increase in canning temperature, bacteria are destroyed five times faster than are vitamins, flavor, color and texture. Accordingly, in contrast to boiling water canning, heat sterilizing in a pressure canner at 240° F (116° C) (10 p.s.i.) destroys bacteria about 17 times faster than chemical changes are effected, accounting for better nutrient and quality retention of pressure canned low-acid foods.

Be cautious about interpreting this as an advantage in pressure sterilizing acid foods. This technique can increase quality and nutrient losses because of the total time the jars of food will be near or above boiling water temperature.

For example, with tomatoes it takes about 5 minutes until steam begins to escape, 10 minutes to exhaust the air, about 5 minutes to build up pressure, 5 minutes for heat sterilizing at 240° F (116° C) and 30 to 45 minutes cooling before opening the canner. That adds up to about 55 to 80 minutes at temperatures near or above 212° F (100° C), as compared to the recommended 35 minutes for heat sterilizing in a boiling water canner. Assuming the average product temperature is elevated above 212° F (100° C) about half of this total time, the loss in quality could be at least doubled.

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.

Freezing

Freezing, like canning, does not improve food quality. Top quality fresh fruits and vegetables are essential for premium frozen products. Quality factors include a suitable variety for freezing, optimum maturity, and freshness of the product. Even with high quality, fresh produce, it is imperative to freeze foods on the day when they are at their peak of maturity or ripeness for eating fresh.

Selection, sorting and trimming of produce and the quality control steps as related to color, flavor, and nutrient retention described for canning high quality fruits and vegetables apply equally to preservation by freezing. However, most vegetables must be blanched before packaging and freezing to prevent slow but accumulating effects of enzyme activity and autoxidation. These effects, if not prevented, will cause discoloration, oxidized flavors (sometimes described as tasting grassy or hay-like), and increased loss of vitamins, especially A and C. Proper blanching recommendations are contained in the USDA Home and Garden Bulletin No. 10, Home Freezing of Fruits and Vegetables.

The quality of packaging materials used is reflected in overall quality of the frozen product. Packaging materials must be moisture-vapor-proof. This means there is no transfer of liquids or vapors from the inside to the outside, or from the outside to the inside of the frozen packages.

In addition, fruits and vegetables must be packaged in containers with as little air inside as possible. Air left inside will oxidize the food, causing deterioration of color, flavor and nutrients.

Proper sealing is essential for packaging quality frozen foods. If the seal itself is not moisture-vapor-proof, it becomes the weakest part of the package and poorer quality results.

Adequate labeling helps assure that each package of food is used while at top quality. Packages kept too long will be of poor quality. Even with the finest produce and use of the best preparation and packaging procedures, retention of quality in frozen food is affected by how quickly food is frozen, the temperature of food stored in the freezer, and how long it is frozen before eating.

For top quality, avoid freezing per day, more than two pounds of fresh packaged food per cubic foot capacity of your home freezer. Food packages to be frozen should be spread one package deep over the bottom or other areas designated by your freezer manufacturer. The freezer should be regulated to a uniform temperature between 0° F (-18° C) and minus 5° F (-21° C). A freezer temperature fluctuation of more than 5° F should be avoided if possible. Freezing too slowly, temperatures above 0° F, and temperature fluctuations in freezers increase the ice crystal size in frozen food, lower the quality and shorten the shelf life of food. Frozen foods should be used according to the guidelines in the 1974 Yearbook of Agriculture, Shoppers Guide.

Quality frozen fruits and vegetables should have the natural color, texture and flavor of the individual food. There should be a minimum of ice crystals inside the package and no sign of freezer burn.

Frozen foods should be higher in ascorbic acid and thiamin than canned foods. Vitamin C, including that leached into the juices, approaches 90 percent of the value of raw fruits.

Drying

Quality fruits and vegetables can be sun-dried or dried inside using an oven or a food dehydrator. As with other methods of preservation, quality of the final product will depend greatly on quality of the fresh food being dried. Drying does not improve the quality of any food.

A top quality dried product reflects suitable pre-treatment before drying, and adequate drying under proper conditions. Also, appropriate storage after drying is vital to keep moisture from re-entering the dried product.

Fruits may be dried more easily than vegetables, because of their high sugar content and since not as much moisture must be removed to get a quality product. When properly dried, fruits should be leathery and pliable, and have a color characteristic of the fruit. Excessive darkening indicates a less desirable, poorer quality product.

Vegetables must be dried until they are brittle. The color should be characteristic of the vegetable and not excessively dark.

To sum up, nutrient content of foods depends on natural differences, control of deterioration, and handling techniques of food preparation as well as preservation. Therefore, overall nutrient content of a specific fruit or vegetable, whether fresh or preserved, may be about the same.

Top quality, garden fresh foods, served in season, provide the greatest satisfaction when served fresh as table-ready food. Individual preferences for market fresh, frozen canned, or dried food will differ. Since nutrient content is nearly the same, the choice is up to the consumer. Even more important is the choice of vegetables and fruits for a good diet.

For Further Reading:

Food editors of Farm Journal, How to Dry Fruits and Vegetables at Home, Countryside Press and Doubleday & Company (Dolphin Books), 1975. $2.95.

Hamilton, Louise W., Kuhn, Gerald D., Rugh, Karen A., with the food editors of Farm Journal, Home Canning—The Last Word, Countryside Press and Doubleday & Company (Dolphin Books), 1976. $2.95.

US. Department of Agriculture, Home Canning of Fruits and Vegetables, H&G Bul. No. 8, on sale by Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. 45¢.

U.S. Department of Agriculture, Home Freezing of Fruits and Vegetables, H&G Bul. No. 10, on sale by Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. 75¢.