Should you or your dishwasher do the first rinse?

DishwasherFor years, I was a member of the clean plate club.  No, I don't mean I ate everything on my plate but rather that I cleaned my dishes (and silverware and cooking utensils) pretty thoroughly before loading them into my dishwasher. Yep, that's what I did until one surprising evening (while I was loading my dishwasher) a dishwasher repairman appeared on my kitchen TV screen. "Don't rinse!" was his message. He swore up and down that dirty dishes clean up better than well-rinsed ones.  I heard it on TV, so it must be right, right?  But I'm not quick to give up my long-standing assumptions, even if they're erroneous. So I listened, and then I researched.


Here's what the repairman on TV said in defense of not rinsing., a position later confirmed by another repairman who came to my house after I reported that my washed dishes felt sticky.  He agreed with the repairman/TV star: Dishwasher detergent needs some food particles to work on, he explained. It will not further clean already clean items.


When seeking an answer to this important question, who could be a more reliable source of information than a dishwasher repairman? Google, I thought.  There, I found a long list of links on this topic including one from Angie's List. At this site, I read that, although some manufacturers and repairmen say too much human pre-rinsing adversely affects cleaning, others say pre-rinsing, while a waste of water, won't downgrade the cleaning.  Furthermore, not rinsing may lead to gook collecting in the dishwasher mechanism, which can clog up the machine and lead to expensive repairs. However, the majority of google articles took the no-rinsing or minimal rinsing position. 


 Being a very thorough researcher, I next turned to our Shelf Life Advice advisory board scientists for their take on the question.   What did they do in their own kitchens? What do they advise the public to do? Here are the scientific responses I got:


From food scientist Dr. Catherine Cutter: "I would still rinse dishes before putting them in the dishwasher. My thinking is two-fold—first, you want the soap/detergent to work effectively. Removing some of the soil with a quick rinse will allow for better solubility of the soap with the organic load. Second, my dishwasher repairman showed me what happens when you have too much food on the plates: it builds up in the bottom of the dishwasher, and can clog the flow of water, impacting the cleaning ability."


From food scientist Dr. Joe Regenstein: "I sort of side with the non-rinsing position, but I worry about baked- on food particles. If there's a water shortage in your area, don't rinse.  Otherwise, do a quick rinse and only do more if food is caked on. This is often a problem with pots but not often with dishes. The key is to experiment: don’t rinse, and see how the plates look.  If nothing remains, why rinse? Also, remember to clean out the “stuff trap” where particles left on dishes and utensils end up." [Note: Not all dishwashers have this feature.]


From food process engineer Dr. Timothy Bowser,:  "If you are going to run the dishwasher immediately, scrape well and let the dishwasher do the rinsing and washing. Don't duplicate efforts!


However, I like to get dishes fairly clean before leaving them unwashed in the dishwasher for any significant length of time. Here are my reasons:


1. Less food for microbes to grow on.


2. The dishwasher will clean better. Less organic matter means that the soap will be more effective.


3. Food residues are normally easier to remove when fresh or wet.


4. Scraping dishes keeps food matter out of the sewage system, which will reduce the work and improve the effectiveness of the sewage treatment system. This one is a no-brainer for any food processing plant that pays for sewage treatment based on soil loads. The first step in cleaning at a food plant is removal of materials that can hopefully be processed into a product or useful by-product. The next step is usually water rinsing.


5. Water is very precious. Keeping food residues out of the water and reducing wastewater are great goals that help save this valuable resource. Scrape well before rinsing. Find a way to use the scrapings for pet food, compost, or in some other environmentally friendly manner."


So, we learn from Dr. Bowser that many factors may be more important than having shiny dishes. Never before did I consider the global environmental  implications of dishwashing.


Dr. Regenstein points out that one should actually consider the whole environmental issue of whether a dishwasher should be used at all.  "Why not just wash the dishes the old-fashioned way and not use electricity?' he suggests. Washing dishes in a pan of  soapy water (rather than a dishwasher) also minimizes water use."


In most household situations, the scientific consensus among our Board members favors a quick rinse before loading the dishwasher.


Whether all of the above does or doesn't you the definitive answer you were seeking, by now you've probably turned your attention to another significant rinsing question--whether or not to rinse raw poultry. This answer, which also demands that you give up a long-standing assumption, is "No!"  If you don't believe me, check out "Stop! Don't Rinse That Raw Chicken!" It will tell you why not.


Shelf Life Advice visited the dishwasher topic before.  If you can bear to read more about it,

go to "The Right Care for Your Dishwasher and Microwave."


By the way, here's a useful piece of advice (from a dishwasher repairman and a scientist) to cure a dishwasher's annoying habit of  creating sticky dishes:  Pour 1-2 cups of distilled white vinegar into the dishwasher, and run it on high. 




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


Catherine Nettles Cutter, Ph.D., Pennsylvania State University, Department of Food Science


Joe Regenstein, Ph.D., Cornell University, Dept. of Food Science  "Do You Need to Rinse Dishes Before Placing in Dishwasher?"


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