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When it comes to sterilizing canning jars, the process for sterilization depends a great deal on the method being used in canning and how long the process takes. Someone using a water bath canning method for jars, for example, only needs to sterilize the jars if the canning process will take less than 10 minutes, or more depending on altitude. When sterilization is necessary, it can be done by submerging the jars in boiling water, and keeping them clean and warm until ready. Someone using a pressurized canner, regardless of time, does not need to worry about sterilizing canning jars.
While all jars used in canning should be cleaned, there are some situations in which a canner should consider sterilizing the jars prior to use. This sterilization can typically be done quite easily, by placing the jars right side up in a large pot, usually the one being used for water bath canning, and covering them with hot water. This water is then brought to a boil and remains at a boil for 10 minutes to ensure proper sterilization. Anyone considering sterilizing canning jars at altitudes higher than 10,000 feet (about 3.05 kilometers) should add one minute for every 1,000 additional feet (about 305 meters).
Once the jars are sterilized, they should be removed from the hot water and placed to the side. Prior to sterilization, the jars should be cleaned either by hand or in a dishwasher. Once the jars are sterilized, then they should be kept clean and hot; one of the easiest ways to do this is for a canner to keep the jars in a hot dishwasher until they are ready for use.
After sterilizing canning jars, a canner should be careful to keep the lip around the edge of the jars clean during use. Using a funnel to fill jars can make this process easier, and once a jar is filled to the appropriate level for canning, the lip should be wiped off with a rubber spatula and a clean towel. This ensures the lid of the jar can form a proper seal during canning.
The process of sterilizing canning jars is not always necessary, though the jars should be cleaned and kept hot prior to use. This requirement for sterilization depends on the recipe being followed and the time required by that recipe for the actual canning process. In water bath canning, if the recipe itself calls for the canning process — once the food is in the jar — to last for 10 minutes or longer, then sterilization prior to canning is typically not required. This time depends on altitude, however, in the same way as the standalone sterilization process.
Anyone who is doing pressurized canning, rather than water bath canning, also does not need to worry about sterilizing canning jars prior to their use. Once again, however, they should be cleaned thoroughly and kept warm or hot before canning. The high heat and pressure of the canning process sufficiently sterilizes the jars during this type of canning, regardless of how long the canning process takes.