And Now…The Chilling Conclusion!

Last month we started to investigate the idea of freezing one’s jeans as a means to kill invading bacteria and thus essentially “cleaning” your pants. What mainly bothered us about this idea was how so many people could accept it and promote it without really questioning the facts behind it.

Like any good scientists, after copious research we developed some hypotheses:

  1. Freezing jeans (in a conventional freezer) won’t actually kill any bacteria living on them
  2. The bacteria on jeans will freely grow again when removed from the freezer
  3. There is no difference between freezing jeans for a day versus a week
  4. The actual amount of bacteria present on a regular pair of jeans is negligible, so you probably don’t need to worry about it; and
  5. Matt will still not be OK with unwashed jeans

To facilitate the experiment, I wore the same pair of jeans every day for about 2 weeks straight. I considered even wearing them to bed, but this seemed like over dedication. A second victim volunteer wore another pair for 1 week. Matt declined to participate.

Kitchen Agar!!!

Seeing as this was the first time either of us had made agar plates in a kitchen, we were pretty impressed with how well they turned out.

Using sterilized cotton swabs (dipped in sterile water), samples were taken from the inside of the jeans on the upper thigh (a high-friction site), as well as from the leg of the individual.

Genevieve's Pants! (and toes)

Pants of our volunteer. And more toes

In total, we had 9 different samples:

  1. positive control (swab from inside the mouth of a child –> full of bacteria)
  2. negative control
  3. swab from Genevieve’s left pant leg
  4. swab from Genevieve’s right pant leg
  5. sample from Genevieve’s right thigh
  6. swab from volunteer’s pants
  7. sample from volunteer’s thigh
  8. and 9.  samples from jeans after freezing

Inoculated plates were incubated at a temperature of around 33°C/91°F for 3 days to facilitate visual growth.

Sure your incubator can hold 97 +/- 0.0005 degrees, but can it make coffee?

Labelling things in the freezer is important.

After the samples were collected, the dirty jeans were placed in sealed plastic bags with as much air removed as possible. One pair (Genevieve’s) were left in the freezer for 24 hours while the other pair remained frozen for a week.

And finally RESULTS!!!

At first we were worried because NOTHING was growing on any of the plates.  And while this could have indicated no bacterial growth what-so-ever, proving our point through a lack of observable results just seemed anti-climactic.

So we did what any self-respecting scientists (with well documented impatience issues) would do: we established a positive control by sampling the known bustling bacterial haven of a child’s mouth.

Our negative control sample. Possibly a tiny bit contaminated??

Positive control. DEFINITE contamination!

                                                          Alright, so bacteria is found were we expect it to be found.

Wait – “I blame Matt” in the mouseover text? I’m offended Genevi.

Hurt even?

Wounded, Genevi.


Bacteria from Genevieve's leg; ...............pants before freezing;.................. and after 24 hours in the freezer

And there you have it. Apart from the debatable presence of a tiny colony on the negative control, it shows that any bacteria growing on the plates came from the sample source, not the sampling method; meaning that if the freezer were capable of killing bacteria and sterilizing jeans, the “after” samples would have no colony forming bacteria at all. Evidently this is not the case after 24 hours…

Bacteria from volunteer's leg;....................pants before freezing;........................and after 1 week in freezer

…or even after a week. This might be a small scale test, but the results are hard to argue: freezing your jeans does not kill bacteria, it only makes them colder. I dare say that all our hypotheses are strongly supported (number five is confirmed) by these findings. At the risk of repeating ourselvesalways read critically and  question ‘scientific’ advice from the internet. Yes, even ours. And here’s why:

Ideally this experiment would have included samples from different areas on the jeans (like behind the knees, lower leg, perineum) and we would have tested more than two pairs and tested them after washing and done a statistically significant number of runs. But we only had 9 Petri dishes. Oh the limits of thrifty science (we do accept donations). However, if you happen to have access to some agar and dirty jeans and if you have some spare time, give our results a little more robustness by repeating the experiment. Share your results in the comments! We would love that!

I think it’s safe to conclude, as others have, that freezing your denim will not, in fact, rid it of any bacteria that might be currently freeloading. If you want to remove the microbes wash them in hot, soapy water. If however, you are not bothered by the bugs (and really, there’s so few actually residing there) and you value the longevity of your expensive threads – freezing them might make them smell a little fresher.  But overnight is definitely sufficient. A week in the freezer is overkill (minus any actual killing). Also, I bet that just hanging them up outside would work too.

A special “thanks” to Y’Amy for helping us get the needed equipment and agar for this experiment, and to “anonymous friend” for not washing your pricey pants in the first place and making me question it.

And also to Scott Pilgrim!
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One Response to And Now…The Chilling Conclusion!

  1. Pingback: To Freeze or Not to Freeze (seriously, this is an actual question) | Quick! To The Lab!

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