I manage an academic microbiology research lab. My question is why do our microwaves keep breaking? We have to replace them about every other year. I'm hoping a microwave expert can give us advice on how to adapt our process that will make our equipment last longer.

We only use the microwave for one thing, to melt agar. We prepare agar media (similar to gelatin in water) in glass bottles, cook and sterilize them in an autoclave (basically a giant pressure cooker). We then let the bottles cool and solidify to store them on the shelves, and when needed, microwave the bottles to re-melt the agar so we can dispense it into Petri dishes. If allowed to cool, the bottle will re-solidify and then it can go back into storage; put it back in the microwave and it melts again. 

At full power, the agar melts too quickly, and can boil over and blow out into the microwave cabinet. This makes a huge mess and of course can gum up the vent mesh in the interior (as you see here in this old photo). Instead, we set it to 50% power, run it for longer (about ten minutes) and this usually prevents boiling over, but not always. The bottles are only ever filled halfway (so a one-liter-capacity bottle only holds 500ml of working media), to reduce boiling-over. 

This process generates a little steam, not a lot - no more than reheating a bowl of soup. We need an interior that is tall enough to hold the 1L bottles, so the machines have all been fairly powerful. We use the microwave this way a few times a day... I estimate the microwave is operating 4 hours a week at 50% power. That's probably more than typical home use, but not significantly more, imo. 

My best guess is that some agar that has boiled over enters the magnetron or some other electrical component as it blasts through the mesh venting. The failure results in a grinding noise and a sparking sound from the magnetron (I presume). 

Admittedly, some students "forget" to clean the microwave when their media has boiled over, and if no one 'fesses up, I have to clean it. To do this I just microwave a wet sponge and then wipe it out. 

I'm hoping someone can give me advice on how to preserve the microwave better. If we could cover the mesh with a breathable material like a paper towel or cheesecloth to protect the internal mechanisms, that would be easy. Is that ok in a microwave? Or maybe the problem is something else? 

I'm here for any ideas or advice. Luckily a 150$ microwave is a minor expense compared to other science equipment, but I hate knowing that we are burning through machines that should last much longer, and contributing to landfill waste. TIA! 



Microwave help for a research lab - they keep breaking