December 5th, 2011

One reason that I avoid cleaning, besides being lazy and having better things to do, is that deep down I feel that I am perpetuating filth, not annihilating it. Sometimes the act of cleaning feels so dirty. One reason for this is the sponge. I do not understand the sponge at all. It is counter-intuitive to me. You have this object that absorbs, which makes me feel that germs (and everything bad you’ve wiped the sponge over) are festering inside of the sponge. Keep it a month or more, they say? That’s a month or more of festering! Heat it in the microwave, a trick they prescribe? It smells like sautéed microbes. And now that it’s absorbed a month’s worth of everything you wanted to get rid of, then sweated half of that out into your cooking apparatus, spread it around on other things you want to clean, and make them dirtier.

I have an innate sense of mistrust. I remember being a young child as my mother ran a hot bath for me. I thought about how she could, if she wanted to, drown me in the scalding water. I had no reason to think this; my mother is very nice. Trust nobody, not your mother, not a sponge. Because of this, I can’t seek help in conducting this research on the sponge. I’ll have to do it myself. And then with some curmudgeonly scientist’s method, I’ll have to test it, and prove the good or evil of the sponge once and for all.


After some preliminary research, I am ready to conduct an experiment using the scientific method. I read online that there are three methods for cleaning a sponge:

Soaking with bleach supposedly kills 37%-87% of bacteria.

Microwaving for a minute will allegedly murder 99% of bacteria.

Washing your sponge in the dishwasher is thought to obliterate 99.9998% of bacteria.

But I can’t trust the word of wikihow. I must employ the scientific method, and control all of my variables. For the past ten years, I have worked with students in Chicago Public Schools to conduct science experiments and science fair projects. Resisting the lure of the fancy three-fold display board, I wanted my students to develop true inquiry-based projects and to CONTROL THEIR VARIABLES! I wanted my students to observe, question, research, hypothesize, test according to a controlled procedure, collect data, analyze data, and draw conclusions.

One time a fourth grade team of scientists was testing the affect of gender on the ability to throw a ball. Several boys threw balls and several girls threw balls, and the distance the ball traveled was measured and compared. A usually quiet student, Enrique, noticed that the data seemed skewed. Indeed, Ashya (whose super far distances were outliers) was using a different ball! The scientists decided to retest that set of data, because they determined that the ball was a variable and had thrown off the results. Ah, a method to the madness!

After ten years of forcing students to engage in the scientific method, it is time for me to do the same, to test the affect of these three cleaning methods on the bacteria in a sponge. I will follow the method as I have prescribed it.



Which cleaning method is most effective at removing bacteria from a sponge: the soak method, the microwave method, or the dishwasher method?

I think the dishwasher method will remove the most bacteria from a sponge. I think this because the dishwasher cycle is longer than the soak method or the one minute microwave method. Also, I observe that dishes that come out of the dishwasher are clean, and I usually don’t get sick when I eat off of them, so they probably don’t contain too much bacteria. I observe that items I microwave get heated, but they don’t get clean.

Four new sponges, the exact same brand.
Four petri dishes.
A stove.
A pot.
A microwave.
A dishwasher with cleaning tablets.
A tub for soaking.
A camera.
Regular kitchen surfaces, dishware, and utensils.

1. Open all four new sponges. These sponges will be used for:
a) soak method, b) microwave method, c) dishwasher method c) control (do not clean this sponge before sampling)

2. For three months, wipe surfaces and dishware with all four sponges. Take care to use each sponge as equally as possible by cleaning surfaces and items in quadrants, with attention to area and volume of food. Also control the washing and squeezing of the sponges. Observe and note any noticeable differences in the appearance or smell of the sponges.

3. Create four agar plates. Boil one teaspoon of agar flakes in one cup of water. Reduce to a simmer, and allow agar to dissolve (about five minutes). Put dissolved agar in a jar and swish it around so it’s evenly distributed. Allow it to decrease in temperature. Once warm but not hot, pour a small amount of agar into each petri dish. Be careful to only open a small part of the top of the dish so as not to allow too much air inside. Quickly close the top of the dish. Briefly tip the dish upside down to avoid condensation on the lid. Allow the petri dishes to sit at room temperature. The agar plates will be ready when the agar has solidified into a gelatinous substance.

4. Conduct all three cleaning methods:

4a. The Soak Method (Soak in 10% bleach, 10% water for 3 minutes)

4b. The Microwave Method (Wet the sponge and microwave for 2 minutes)
Warning: Allow to cool before squeezing!

4c. The Dishwasher Method (Place sponge in dishwasher for one complete cycle)

Note: Sponge 4 is a control sponge. Do not clean this sponge.

5. After three months, cut the sponge down the middle and about a half an inch from the end. Wipe each inner part of the sponge over the surface of the agar in the petri dish.

6. Wrap the petri dishes in a dishcloth, and store them in a warm, dark place, such as a cabinet. After three days, observe.


These results are very shocking and confusing. They do not match my hypothesis at all! The petri dish with the most bacteria is the dishwasher method dish, which is the method I thought would be most effective at killing bacteria. The second most bacteria-ridden dish belongs to the microwave, which I hypothesized would be the second most effective. Soak and control methods had almost no bacteria in the dishes, making my results the reverse of what I hypothesized.






If I were to trust this data, I would never clean my sponge. I would become paranoid about something new- that perhaps microwaves and dishwashers grow bacteria on sponges (and… what else…?!).  I’m more apt to mistrust my results, because I know that my implementation of the scientific method may have been flawed.


How was it flawed? What variables was I not able to control or what additional variables may have come into play? First of all, my method of using the sponges evenly for three months was inherently flawed. I tried to divide objects into quadrants when cleaning them, but because we don’t eat evenly in quadrants, and because sometimes guests and other impostors used the sponges during those months, measured cleaning was impossible to achieve. Also, this was my first time making agar plates, and though I tried to wash my hands well when making them and open and close the lid quickly when pouring in the agar, it’s possible that some wayward bacteria got into the petri dishes in the process. Another mistake I made was that I microwaved the sponge for a minute dry, wet the sponge, then microwaved for two more minutes. Maybe the dry microwaving increased the bacteria in the sponge (and by the way, it’s also a fire hazard- oops). Finally, my method for wiping the sponge on the agar is questionable. I cut the sponges and wiped the inside area on the agar’s surface. Perhaps it would have been more accurate to wipe the original surface of the sponge instead. So what will I do? Go on feeling paranoid as I sponge surfaces? Become obsessive compulsive about appliances? Try it all over again? Inconclusive!


While holding high expectations of our students, it’s easy to become disgruntled about the work they produce. For many years I have felt that students could do better science fair projects. I should have conducted my own experiment long ago in order to understand- it’s hard! Many times we ask our students to do things that we haven’t done ourselves, or haven’t done since we were in school. Though this experiment was time consuming (and may not even be over yet), it helped me understand the nuances and challenges of the scientific method. The So Crazy It Just Might Work episode of This American Life explores the passion and diligence required to pursue experimentation for the long haul.

Will I keep pursuing this? Should I start over with four fresh sponges? Or should I learn to live with uncertainty (and bacteria)? What do you think?


13 comments to “Sponges”

  1. I think you should keep pursuing, but next switch to alternatives to sponges. Invent the “new sponge.” Maybe our hands are the best means? I give you a ton of credit for going through this long haul of an experiment. Also, yes, we teachers make our students do things we haven’t done, or wouldn’t necessarily do. It’s good perspective to be on their side of the fence. Thx for testing this out – the results were shocking!

  2. My mom always taught me to pour boiling water over a sponge, let it sit until it cools off, then wring it out. The boiling water should kill everything. (Right?) I use the dishwasher method, too, and if you have a high-heat cycle, the heat would (in theory, at least) kill mucho bacteria. Also, perhaps this is important, I don’t use sponges to wipe up anything bacteria-ish (I use paper towels and disinfectant spray – in fact, I use this method for all counter-cleaning in general), but only to wash dishes.

  3. I’ve always felt that sponges were somehow “icky” and don’t use them. Your experiment has now raised the bar on my trusty “dishrag” which I am now eyeing with distrust. Am I reduced to sacrificing a tree and using paper towels with wild abandon? This is causing a major dither to begin. Thanks, I think. LOL Found you thru Lottie+Doof

  4. Thanks for sharing your own distrust and methods. Do you ever worry about using too much disinfectant, including hand sanitizer? What if we lose our resistance to fighting off bad bacteria by constantly warding off ALL bacteria?

  5. Cool shit Katie. Hey, Reemer & I would like you to experiment and scientifically explore what has more uses: radishes or human toes? My hypothesis is that toes are useless and evolution is gonna do away with them. She hypothesizes radishes are useless. Go figure.

  6. Wow. I am impressed. You have a very high level of commitment to scientific research. Once again, where do you find the time? To validate your data…more trials are a must! I expect a full report in 6+ months. I also hate sponges and toss them out when they get stinky.

  7. You’re all going to keep me busy with inventing sponges, retrials, toes, and radishes. Thanks for the assignments!

  8. Shannon Murphy says:
    December 17th, 2011 at 4:56 pm

    What if instead of using four sponges you cut a single sponge into four quarters prior to employing your different sanitizing methods?

  9. Oh geez, Shannon, that is so smart. It seems so obvious. I feel like a moron for not thinking of that before!

  10. I bought microfiber car-washing sponges at Home Depot a year ago. Whenever I do normal laundry, I wash the sponges, too. I trust a washing machine and dryer more than any of the methods here. Something to try in the future, perhaps.

  11. My friend introduced me to Norwex, they sell microfiber cloths that are embedded with silver. When they dry, the silver kills 99.9% of bacteria in the cloth! I’d love to do my own tests with them, although I trust the lab work I know they’ve done, too. I even started selling it to spread the word!

  12. I always thought my sponges are clean. I clean them in the washing machine on the sanitize cycle with bleach. The cycle runs for about 2 hrs and gets very hot. Therefore, I am pretty confident tat I kill all bacteria present since it is kind of a combination of 2 methods. Then I dry them in a very hot dryer, to kill even more germs. When they start falling apart, I buy more.

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