Occasionally, a canning jar may break during processing. If this is discovered when you take the jars out of the water bath canner after processing, carefully remove the broken jar and its contents. It is less likely, but if you suddenly see fruit (or whatever food you are canning at the time) floating around in your canner during the processing time, you'll know a jar broke. You can go ahead and fish out any big pieces that you can get at and still let the processing time finish for your other jars. Careful! It is hot! Either way, be sure you are careful when you empty your canner of the water. Usually a jar simply cracks and there are no small pieces, but…just in case, be watchful for small glass pieces. Being careful to not expose the jars to extreme temperature changes during canning is the best preventative for jars breaking, as is using a proper rack or something on the bottom of the canner to prevent jars from bouncing around in the water.