Before canning food in a glass jar, it is very important to sterilize each and everyone of them. If you can food in a jar that is not sterile, the bacteria and germs will contaminate the food. All that effort of canning, which is hard work, will be down the drain.
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It's hard enough to have enough stove top and pots and pans to submerge and boil dozens of pint, quart or even 1/2 gallon canning jars.
Wash each and every jar by hand or in the dishwasher. If you do use the dishwasher, make sure that all the residue is rinsed clean.
Allow the jars to dry.
Arrange the glass canning jars in the oven on clean oven racks.
Turn the oven on 225 degrees Fahrenheit.
Allow the jars to cook in the oven for at least 20 minutes before using them.
Leave the jars in the oven, (oven still turned on) until you begin to fill them with the food you are canning. That is unless it's a cold pack item. Most foods are hot when you can them. If you put cold food in a hot glass jar, it can cause the jar to burst. The same goes with putting hot food in a cold glass jar.
When you remove the jars, they will be hot to touch. To keep the jars sterile and keep from burning yourself, use a clean jar handler. This is a very wide tong looking kitchen utensil.