Certain foods, foods with a high starch content in particular swell more than others and require more headspace. Too much headspace and the jar won't seal properly ,and, the pickles at the top of the jar may be discolored or spoiled. If too little headspace is allowed, the food may be forced under the lid, leaving a residue on the sealing surface and possibly prevent the lid from sealing.

 

As a general rule, leave a 1/4 inch headspace for juices, jams, jellies, pickles and relishes.1 inch headspace for low-acid foods, 1/2 inch headspace for acid foods, fruits and tomato. Remove the air bubbles by running a rubber scraper or nonmetal spatula between the food and the pickle jar. Wipe sealing edge of pickle jars with a clean, damp paper towel. Add lids and tighten screw bands.

The acidity of food influences processing. Foods are grouped as "acid" and "low-acid" for purposes of selecting the correct processing method. Acid protects against the growth of unwanted organisms, such as botulinum a/k/a botulism. Thus, heat treatments need not be as intense for foods in the "acid" group as opposed to foods in the "low-acid" group.
 

When preserving low acidic foods, such as tomatoes, the USDA recommends that acid should be added to lower the pH level. This can be done by adding 1 tablespoon of lemon juice or 1/4 teaspoon citric acid per pint of product.
 

 

To process pickles in a boiling water canner, fill canner halfway with water and preheat to 180 F for hot packs or 140 F for raw packs. Load sealed jars into the canner rack [Jar rack] and lower with handles or load one jar at a time with a jar lifter onto rack in canner. Cover canner and turn heat to high. Add water if needed to a level of 1 inch above jars. When water boils vigorously, lower heat to maintain a gentle boil and process pickle jars for the time given in manufacturers instructions.  

To process using low-temperature pasteurization treatment, place pickle jars in a canner filled halfway with warm (120 F to 140 F) water. Add hot water to a level 1 inch above jars. Heat the water and maintain 180 F water temperature for 30 minutes. Use a candy or jelly thermometer to be certain that the water temperature is at least 180 F during the entire 30 minutes. Temperatures higher than 185 F may cause unnecessary softening of pickles. This treatment results in a better product texture but must be carefully managed to avoid possible spoilage of your pickles. Use only when recipe indicates.

After processing is completed, remove jars from canner with a jar lifter and place on a towel or rack. Do not retighten screw bands. Cool jars 12 to 24 hours and remove screw bands. Check lid seals. If the center of the lid is indented, the jar is sealed. Wash, dry, label and store sealed jars in a clean, cool, dark place. If the lid is unsealed, examine and replace jar if defective, use new lids, and reprocess as before. Wash screw bands and store separately. Pickles are best if used within a year but are safe as long as lids remain vacuum sealed.