Canning tipsMany national and state university extension services do not recommend steam canning because of the difficulty of determining the exact heat attained (though it usually is higher than that of the boiling water bath) and the proper time needed to process foods[v]. Yet, many home canners swear by steam canners because they’re quick and easy to use. It takes quite a while for a large kettle of water to come to a boil, but the steam canner uses much less water and is ready sooner. Full water bath canners are extremely heavy, while steam canners are lightweight and easy to handle. Tomatoes take about 45 minutes to process in a steam canner, and fruits such as pears, peaches, apples’ or grapes about 20 to 30 minutes. If you choose to use a steam canner, follow the instructions very carefully and remember that steam canners are never the right choice for canning vegetables or meats[vi]. Regular pressure cookers are not recommended for canning because their thinner walls and smaller size do not allow for correct build-up and reducing time of the pressure, thus failing to destroy all harmful organisms. Use pressure canners that are specifically intended for that purpose. Do not allow the pressure to drop during canning. If the pressure drops below the recommended level, increase the heat to bring the canner back to the proper pressure and start the timing process all over again from the beginning. Even if your product is a little overcooked, that’s far better than spoiled. If you live at an altitude higher than 1,000 feet above sea level, read your canner’s instructions on increasing time or pressure level. Be sure to vent the canner with steam exiting for the specified length of time to prevent air becoming trapped in the closed canner, as trapped air lowers the pressure and results in under-processing. Use quart or pint-sized Mason jars, not old mayonnaise or pickle jars for processing. Mason glass is thicker and tempered to withstand the needed heat and pressure without cracking. Wide-mouth or regular openings are fine. Use new lids and clean rings that are round, not warped or rusted. Half-gallon jars are not recommended for home canning. Be as clean and careful as possible in preparing your jars and your food. Wipe the jar rims with a clean cloth or paper towel before putting lids on. Follow all instructions carefully.
[i] http://nchfp.uga.edu/publications/usda/GUIDE%201%20Home%20Can.pdf [ii] http://extension.usu.edu/utah/htm/fcs/food-preservation-canning/canning-101 [iii]http://nchfp.uga.edu/publications/usda/GUIDE%201%20Home%20Can.pdf
Our extension office teacher on canning said always buy and use new lids, not the ones that originally come with the jars, as too many of them often have fine bends in the metal, resulting in improper seal. She recommends never using a lid twice because the rubber is thinner than it used to be and may not make a proper seal the second time it is used.