What is the best way to sterilize a cleaning cloth?

I think it is fine to use one Norwex cloth, e-cloth, or cotton washcloth for the whole day of wiping up the kitchen as long as you didn't use it to wipe up raw meat. I suggest hand washing it between uses and hanging it up to dry. However, at night (or after wiping up raw meat), I recommend retiring that cloth until it can be properly cleaned. Then get a new, clean cloth out the next morning and start each day with a fresh one. But what is the best way to really get the germs out of the cloth? 

Washer and Dryer

The easiest way to clean a cloth would be to put in a hot washer and a hot dryer. Surely, washing on hot and an hour in a hot dryer will kill all the germs, right? I've always assumed that. However, I needed to actually test it. 

 First, I drew 3 circles on each cloth with permanent marker and put 1mL of dirty water (made with mud from the back yard) onto each circle.


I tested a Norwex cloth and a cotton washcloth. 


I pressed one dirty spot from each cloth onto an agar plate as the dirty controls. 



Then I washed the cloths on the hot normal cycle in my 1 year old HE Samsung top loader. After the cloths were done in the washer, I pressed the second dirty circle from each cloth onto an agar plate. Then the cloths spent an hour in my  Samsung dryer on the sanitize setting. After coming out of the dryer, I put 1mL of sterile water onto the 3rd circle of each cloth and pressed that onto an agar plate (because the cloth needs to be wet to efficiently transfer germs to the plate). The plates were incubated for 24 hours. 


Much to my dismay, the cloths were still not germ-free even after going through the washer and dryer! This experiment has been repeated many times. In fact, it has spawned a whole month of washer/dryer laundry experiments and you can see those results on my laundry page. If you have a cloth that can handle chlorine bleach, then it will USUALLY get very clean in the washer and dryer. However, some cloths like Norwex and Silvertize say NOT to use chlorine bleach. I have sense gotten a new Whirlpool front loader that has a sanitize cycle. Washing your cloths on a hot sanitize cycle does not do as well as bleach but is probably fine. You can see my laundry page for more information about that. 

Here are the results of an experiment where I compared hand washing to machine washing of two Norwex cloths. I put the 1mL of germ water (with lots of dirt and bacteria) onto the circles on each cloth. I hand washed one cloth for a total of 4 minutes using hot (120 degree F) tap water and Norwex detergent. The machine washed cloth was done in hot water with Tide Free and Clear detergent. Then I dabbed the "clean" cloths onto agar plates. 


As you can see, the machine washing did better than the hand washing, but it was not STERILE like I had hoped. Some cloths, like Norwex and Silvertize, say not to use chlorine bleach on their cloths. If you use regular cotton cloths for cleaning then you can use chlorine bleach in the laundry and that usually does an outstanding job killing germs. See my laundry experiments for more info on washing with chlorine bleach. 

BOILING

Boiling is more labor intensive than the washer and dryer, but it would certainly kill all the germs, right? Laura Ingalls describes in detail how they boiled all their laundry once a week in her "Little House on the Prairie" books. I always assumed that if a germ was in boiling water for a mere 2 seconds, then it would die. So, I did an experiment where I drew 3 circles on my cloths with marker. I put 1mL of dirty water on to each circle. I pressed one spot from each cloth onto an agar plate for the dirty control. Then I boiled the cloths for 2 minutes, 5 minutes, or 10 minutes. I stirred occasionally while the cloths were boiling because they would balloon up, and I had to push them back under the water.  

After the cloths were boiled, I let them cool briefly on my drying rack and then pressed the formerly dirty circles onto an agar plate. The plates were incubated for 24 hours. I tested Norwex, e-cloth, and cotton cloths over the course of a few experiments. 



I don't know about you, but I am STUNNED that any bacteria could survive 2 minutes of boiling! There were even a few colonies that survived 5 minutes of boiling! So, boiling does a great job sterilizing a cloth, but it is best to boil for a full 10 minutes. 

Soaking in HOT water

One Norwex consultant suggested that I just soak the cloths in very hot water instead of boiling them. So, I boiled water and then took the pot off the burner for a few minutes to cool it a little. Then I soaked the cloths (that had dirty water on them) for 10 minutes. 

For this experiment, the cloths were soaked for 10 minutes in water that went from 200 degrees F down to about 160 degrees F during that 10 minute period. I am shocked that there were still some live germs on the cloth. 


In this experiment, the cloths soaked in water that went from 180 degrees F down to 160 degrees F during the 10 minute soak. There were a TON of live germs. It is mind boggling? Don't we only need to cook chicken to 170? How can this be?


I wondered what the heck was going on. Were there tiny bubbles on the cloth protecting the bacteria? Perhaps it was the STIRRING that was making the difference. In the boiling experiments, the cloths were constantly moving around. However, in these experiments, the cloths were just soaking without being agitated at all. So, for this next experiment, I stood at the stove and stirred for the entire 10 minute period. (It was a huge pain to stand there and stir for 10 minutes. If it is not homemade chocolate pudding, it just isn't worth it.)


As you can see, almost all the bacteria died when the cloths were soaking in the hot water (200 degrees F down to 160 degrees F) for 10 minutes when I stirred. So, agitating is a whole lot more important than I originally thought. I still don't fully understand all of these results, though. For now, I'd suggest just boiling for 10 minutes any cloth that you want to sterilize with occasional stirring. Feel free to consult the manufacturer of your favorite cloth to find out if the cloths can withstand repeated boiling. 

Microwaving


Microwaving would be an easy way to sterilize the cloths so I decided to test that. I made germ water that contained dirt from the back yard (so it is a totally reasonable amount of bacteria that you would likely encounter while cleaning regularly). I got the cloths wet and rung them out. Then I folded the cloths over twice and put 4 mL's of germ water on each cloth. I put 2 mL's on the top of the cloth and 2 mL's on the inside, because I wanted to see if the microwave would "cook" the different layers evenly. After microwaving, I let them cool for a minute and pressed the dirty spots onto an agar plate. I tested 2 different Norwex cloths and a cotton cloth in these experiments. 


I microwaved them on a paper plate. 


I covered the cloth with a paper plate too. 

I microwaved for various time periods. As you can see, 1 minute and 2 minutes were not long enough to kill all the bacteria. I also took the temperature of the cloths after 2 minutes using my meat thermometer and they were about 180 degrees F. 

3 minutes was not long enough to kill everything. 

5 minutes did not quite kill everything either. 

So, microwaving certainly killed a lot of germs, but I was never able to get the completely sterile cloth that I got with 10 minutes of boiling. I was afraid to microwave the cloth longer than 5 minutes. I wasn't quite sure if anything bad would happen. 

Just to compare, here is what grows when I press a piece of Bounty paper towel onto an agar plate (after wetting it with sterile water.) 

Nothing grows. A roll of paper towel is pretty sterile. 


CONCLUSION


I think the Norwex cloths and e-cloths are great to clean with. I love how they glide over the surface. I've tested and shown that Norwex and E-cloth pick up more germs than even a Clorox wipe! But at night, mine goes into the laundry basket, and the next day I get out a clean cloth. Of course, if you wipe up raw meat or raw chicken, that cloth needs to be immediately retired to the laundry or boiled. If you feel comfortable using the same cloth for several days, that is up to you. But know that the cloth is most likely full of bacteria. If you are interested in purchasing Norwex cloths, you can buy them here. E-cloths are available on amazon.
It is certainly a lot harder than I expected to get the germs out of any cloth. 10 minutes of boiling is ideal but washing on hot in the washer and dryer is more convenient and, hopefully, good enough. My laundry experiments showed that if your washer has a sanitize cycle that might be good enough. Using chlorine bleach in the laundry usually does a great job but some cloths can't handle bleach. Of course, now that I know how difficult it is to get all the germs out of a cloth, I will personally be wiping up raw meat, vomit, or diarrhea with paper towel and not even attempting to clean that stuff out of a cloth. I will still be using my e-cloths and Norwex for most of my regular cleaning, though. Please realize that while the cloths are great, they are not magic. Be smart, you should not be wiping up raw chicken and then wiping off the baby's highchair tray because you think the cloths couldn't possibly transfer germs.