Hello Linda,
Using a microwave to sanitize glass jars is a common shortcut among home cooks, but there are several critical safety rules and food preservation guidelines you should know before attempting it.
First and most importantly, you must never put metal lids, rings, or jars with metal wire bails into a microwave, as metal will spark and can cause a fire or damage your appliance. Any metal components should be sterilized separately in a small saucepan of simmering water on the stovetop.
Second, never microwave dry glass. Dry glass does not absorb microwave energy well, which creates thermal stress and can cause the glass to crack or explode. If you use the microwave method, wash your jars thoroughly in warm, soapy water, rinse them, and leave about an inch of water at the bottom of each jar. Microwave them on high power for about 45 to 60 seconds, or until the water boils and generates steam throughout the jar. Always use clean oven mitts or jar tongs to remove them, dump out the residual water, and fill the jars while they are still warm so the glass does not experience thermal shock from hot jam.
Lastly, from a professional culinary and food safety standpoint, microwave sterilization is not officially recommended by food safety authorities for shelf-stable home canning. Microwaves heat unevenly and may leave cool spots where mold spores or bacteria can survive. If you are making a quick refrigerator jam that will be consumed within a few weeks, this quick steam method is generally fine. However, if you plan to store your jam in the pantry for months, boiling the jars in a water bath for 10 minutes remains the safest and most reliable method.
I hope this helps you make the most of your sale fruit, and happy jam making!
