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. However, the success of the germ-killing totally depends on your particular washer and dryer and the heat. If you are washing on cold, then your cloths still have lots of germs. If you have a washer that only gets up to about 120 degrees F, it won't kill many germs. You can see how dirty most people's "clean" laundry is on my laundry experiments page. 

However, I use my Whirlpool duet HE front loader on a hot sanitize cycle with extra rinse and steam boost (2 hour cycle) and it does very well killing germs. I also use the sanitize setting on my dryer. 

I press the cloths onto agar plates like this to test them. 


Results from Whirlpool duet sanitize cycle and sanitize cycle in dryer




Here are results from my old HE Samsung top loader that I do not recommend getting at all. I washed a dirty Norwex and a dirty cotton cloth on a hot cycle and dried them in my same Samsung dryer on sanitize. They did not get nearly as clean as my new Whirlpool washer gets them. 
So, my cloths get clean enough in my washer with the great sanitize cycle. I have noticed that they get cleanest in a small load of just the cleaning cloths. My other laundry experiments show that larger loads have more germs even on the same sanitize cycle. So, if you wash your cleaning cloths on the hottest, longest sanitize cycle in a tiny load of just your cleaning cloths and then put them in the dryer, they probably won't be perfectly sterile, but I think they will be fine. 

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 recommend using a clean cloth each day and retiring it to the laundry at night. Wash them in the hottest, longest sanitize cycle that you have in the washer and dryer, or boil them to kill the germs. Of course, my laundry experiments show that using chlorine bleach is second best (after boiling) for killing germs, but lots of fabrics can't handle bleach. 
 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. E-cloths are available on amazon.