The Right Care for Your Dishwasher and Microwave

Dishwasher getting vinegar treatmentFor the dishwasher or microwave to get our attention, it usually has to stop working.  But that shouldn't be the case. If we don't treat our appliances with care, they are likely to mistreat us. Does a dishwasher need cleaning? If so, why and how? What shouldn't be heated in a microwave? Below are responses to these questions and other important matters concerning these appliances from 3 scientists who serve on our site's Advisory Board and from companies that manufacture these appliances.


The Dishwasher: Mostly about Cleaning


Here's the one and only safety message I found in my dishwasher instruction booklet (worded differently):  If you're eager to avoid an electrical shock, a fire, and/or death (as the vast majority of us are), be sure that your dishwasher is properly grounded.  The dishwasher ground wire should be attached to the ground connector in the terminal box or plugged into a grounded 3-prong outlet.  Further instructions regarding either method: don't use an extension cord.  Further instructions if the dishwasher cord is plugged in: don't remove the ground prong, and don't use an adapter. 


Now, on to the matter of cleanliness. Your dishwasher needs your help in staying clean. It may sound incongruous to tell you that the machine that cleans your dishes and silverware needs cleaning itself, but it makes sense because food particles and chemicals in hard water can affect the dishwasher's ability to clean well.  Here are some suggestions from our Advisory Board scientists:


Advice from food process engineer Dr. Timothy Bowser:


  • Dishwashers can accumulate food and trash in the trap or strainer going to the drain (if your dishwasher has this feature). Strainers need to be removed, emptied, and cleaned periodically.
  • If food pieces have accumulated in any other areas inside your dishwasher, clean them out by hand.
  • Mineral deposits can build up in your dishwasher, especially if you are using hard water. A good cleaner will help to remove deposits and keep the interior surfaces of your machine clean and spot-free. 


Advice from food scientist Dr. Joe Regenstein:


  • ŸThe screen at the bottom of a dishwasher can accumulate waste, which needs to be removed.
  • In hard water situations, there can be a build-up of scale (calcium chloride).


Advice from food scientist Dr. Catherine Cutter:


  • Vinegar gets off some of the scale from hard water deposits.  Place one cup of vinegar on the top shelf, and run the dishwasher with just the vinegar and water.  The vinegar treatment will also help to get glassware looking brighter. You can run the dishwasher with nothing in it except the cup of vinegar or add glassware that shows scale. The idea is to distribute the vinegar onto the surfaces to remove the scale. It’s antimicrobial as well!
  • Be careful about following cleaning advice from internet articles until you check with the manufacturer of your dishwasher.  Note Dr. Cutter's responses to the suggestions mentioned in "Your Dishwasher is Filthy--Here's How to Clean It": "I watched the video. My dishwasher doesn’t have this kind of filter. In fact, when we had the dishwasher serviced last month, the repairman had to dismantle the entire dishwasher to get to the filter (which turned out to be clogged and damaged). Also, I would be cautious about recommending the vinegar and baking soda bombs that they made in the video. It’s important to check with the manufacturer of the dishwasher and make sure these types of chemicals won’t damage the machine or void the warranty."
  • The dishwasher may need cleaning and disinfecting around the inside edges of the door since this is a great spot for mold growth.  Wash with warm soapy water, then disinfect with a disinfecting wipe or spray.  (Do not reverse the order.  Washing with soap must precede disinfecting.)


 The Microwave Oven: How to Avoid Explosions and Burns


Safety tips from microwave manufacturers:


  • Metal utensils and foil can cause arcing (sparks).  Arcing is likely to occur when metal touches the sides of the oven.  It's best to avoid using silverware, twist-ties, poultry pins, or gold-rimmed dishes in the microwave.  When heating a packaged frozen dinner in a foil tray, be sure that the foil does not touch the sides of the microwave. [Dr. Regenstein points this out: "Ideally, the product will have microwave instructions, which often include keeping the product in the outer box.  Some of these boxes are specifically designed to help a microwave work better."]
  • Don't try to cook or reheat a whole egg (peeled or unpeeled) in the microwave.  It could explode due to pressure building up inside the yolk.  (I know of two people who had this type of accident, and one of them was me! It was messy.) 
  • Don't heat food in glass containers even after the lid is removed (for example, on baby food).
  • Don't use these in the microwave: paper bags (except for popcorn bags designated for microwave use), Styrofoam plates and cups (because these can melt and leave harmful chemical residue on your food), plastic storage and food containers (that are meant for the refrigerator or freezer and may melt in the microwave).  [Note: Some plastic containers are marked as microwave safe.]
  • Don't use the microwave to try to defrost a frozen beverage in a narrow-necked bottle, especially a carbonated beverage.  Pressure can be build up, causing the container to burst. This can happen even if the cap is off the bottle.
  • Beware of superheated water. Liquids (especially water, coffee, or tea) can be overheated, thus reaching temperatures that are higher than the boiling point.  Then, these liquids could boil over when the container is moved or a utensil is inserted.  To avoid this, don't overheat these liquids, stir when about halfway through heating, allow the container to remain in the microwave for a short time before removing it, and be careful when inserting a spoon into the hot beverage.  For more information about this dangerous rare phenomenon, go to the Snopes article "Boil on Troubled Waters."
  • In general, food products sealed in plastic should be slit or a corner lifted to allow steam to escape (unless the package says not to do so).
  • Microwave popcorn in a bag only if the bag it comes in states that this is safe. 


Note:  Your microwave booklet probably contains a lot more safety tips.  If you haven't looked at it for a long time, reread it!


Microwave safety tips from Dr. Bowser:

  • ŸClean the oven regularly to prevent bacteria buildup.  Do not use metallic scouring pads or steel wool.
  • Do not heat foods containing flammable liquids in your microwave.
  • Products that have natural skins (like grapes, whole-kernel corn, or potatoes) may explode or   erupt suddenly when the inner material expands or water evaporates and bursts through the skin. The solution is to pierce the skin to allow the inside materials and/or steam to escape during heating. [Editor's note: Some other foods that should be pierced before microwaving are hot dogs, sausages, tomatoes, apples, chicken livers and other giblets, and egg yolks.]
  • Some foods tend to unexpectedly explode or erupt during or after microwaving. I have experienced this with foods that have heated unevenly and have a hot spot that is unstable (e.g. tomato sauce).  [Editor's note: Stirring foods at least once when they're only partially heated is a good idea. If your microwave has a “rotator” in it, use it. If not, you might want to consider buying one. Microwaves do NOT heat evenly; therefore, during the cooking process, don't keep the food in the center of the microwave all the time; move the container around once or twice.]


Your Shelf Life Advice editor's thought:  Don't let children use the microwave until they're old enough to understand how to use it safely.  Remind them that what they're removing from the microwave could be very hot; it should be done with two hands and two potholders. 


For more information about microwave safety, go to this Shelf Life Advice page:


Additional links to information on microwave usage (including using plastic in the microwave) can be reached by typing "microwave" into the search box on the Shelf Life Advice home page.





Timothy J. Bowser, Ph.D. , Oklahoma State University, Dept. of Biosystems and Agricultural Engineering


Catherine N. Cutter, Ph.D., Pennsylvania State University, Dept. of Food Science


Joe Regenstein, Ph.D., Cornell University, Dept. of Food Science


Microwave Oven User Manual by Haier


Microwave Oven for General Electric oven


Installation Instructions, Undercounter Dishwasher by Kenmore



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