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Rotten potatoes have a distinctive unpleasant odour, and I can't find any definitive answer as to what the chemical involved is. I was thinking it might be Butyric acid, from the fermentation of the starch, but according to Wikipedia:

Butyric acid is present in, and is the main distinctive smell of, human vomit.

And those puppies don't smell like vomit. They're more like rotting flesh – the reason I'm asking is that I've spent half the day looking for a dead animal that the cat brought in or something, only to discover that the horrible smell was coming from the potato box.

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    $\begingroup$ Just as a side note, you can delay the putrification of your potatoes by putting them in the refrigerator crisper drawer. They will literally last at least 10 times as long in the refrigerator. And trust me I have tested this Theory multiple scientific ways & the refrigerator does the job..! Please do not get the mean idea of messing with your friends by putting a potato under the driver seat or another enclosed area where they might like to hang out in. You will not be able to hold in your Chuckles and you will get busted by your friends.! $\endgroup$
    – Bill Watson
    Commented Jun 2, 2019 at 7:57

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My first guess was that it was putrescine and other polyamines---but the smell of putrefying potatoes actually comes from methyl mercaptan, dimethyl sulfide, and dimethyl trisulfide. Check it:

enter image description here

Source: A. Kamiya, Y. Ose, Study on offensive odor (Report IV): A Consideration of Putrefaction and Offensive Odor of Solid Waste, Journal of Japan Society of Air Pollution, 18(5), 1983, pp 453-463.

Notice that the headspace composition changes quite a bit with time. Most of the headspace chromatography studies I found dealt with early detection of disease organisms in infected potatoes, rather than potatoes in full putrefaction mode. You'll also find many references to solanine poisoning from potatoes; solanine is a toxic glycoalkaloid, is nonvolatile, and has nothing at all to do with the foul smell and toxic gas produced by putrid potatoes.

Methyl mercaptan ($\rm CH_3SH$) has an odor described as "rotting cabbage" by ATDSR; it's one of the major contributors to the smell of farts (oh, sorry, "flatus" if we're being polite). It has an odor detection threshold as low as 1 ppb.

Dimethyl sulfide ($\rm (CH_3)_2S$) is responsible for the smell of the sea (in low concentrations); it too has a cabbagy smell.

Dimethyl trisulfide ($\rm CH_3SSSCH_3$) is present in relatively smaller amounts but it has an even stronger odor. The detection threshold is around 1 part per trillion, and it is apparently a strong insect attractant.

The gases produced by rotting potatoes are quite toxic (see Rotting potatoes in basement kill four members of Russian family).

(To keep the notes below in context, in my original answer I said that a plot point in "The Walking Dead" was that zombies couldn't smell delicious humans if they were wearing coats smeared with rotting flesh. I suggested that when the zombie apocalypse arrives, packing your pockets with putrid potatoes might work, too. Now I'm not so sure. Can zombies distinguish between polyamines and sulfur compounds? Perhaps they're stench connoisseurs.)

enter image description here

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    $\begingroup$ There is a fact which is important when describing/discussing strong odors of sulfurous compounds: the odor can vary very much by concentration and with time spent in an atmosphere with such odor. It can switch from bad to pleasant at some concentration, or the odor vanishes completely. A common example is the extreme pungend stink of craft cellulose plants, which vanishes at the second or third breath takin. Otherwise such plants were not possible even in rural areas. $\endgroup$
    – Georg
    Commented Jan 23, 2015 at 21:09
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    $\begingroup$ @Fred Hi, can you please share the links to those paid research papers that you were talking about, which are actually working on the early stages of potato rot. I am studying these papers for acedamic purposes. Also, I couldn't comment on the above thread as I am new here. $\endgroup$
    – Jai Aggarwal
    Commented Mar 8, 2016 at 7:10
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It is a combination of potato and a fungus or bacterium that causes a potato to rot and produce the offensive odor. A major contributor to the odor is dimethyl disulfide which has been identified as a key component of the emitted volatiles (see here)

enter image description here

Although the above reference doesn't mention it (at least not in the abstract) dimethyl disulfide is often accompanied by hydrogen sulfide, dimethyl sulfide and dimethyl trisulfide, the trisulfide being particularly odiferous.

Not only is the odor of rotting potatoes extremely unpleasant, but it has been reported to be lethal. Certainly eating rotten potatoes can be lethal (solanine poisoning).

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  • $\begingroup$ Thank you for this! I wonder, though, if this study wasn't geared towards early detection of disease rather than advanced decomposition? They seemed to be focusing on headspace gases that were produced directly by the organisms. I couldn't read the paper from where I am right now because it's behind a paywall. $\endgroup$
    – Fred Senese
    Commented Jan 23, 2015 at 13:39
  • $\begingroup$ @FredSenese Yes, these authors have published several papers on early potato rot detection methodologies. My assumption was that rot is a relatively simple process involving a simple pathogen and a potato, and composition of the volatile mixture won't show much variation with time, but I don't "know" that. I was also wondering about your answer. Everything living contains putrescine, more in animals, less in plants; but not everything dead smells like putrescine. Do you have any data or reference that supports your answer of putrescine vapor in the air around rotting potatoes? $\endgroup$
    – ron
    Commented Jan 23, 2015 at 16:05
  • $\begingroup$ True. And alas, I don't. I haven't done a thorough search. My answer was just a hypothesis, not a definitive answer. Maybe I'll pop a rotten spud into our headspace GC sometime. All of the papers I've seen in a quick go with Google Scholar focus on early detection, rather than advanced decomposition. For example, this one onlinelibrary.wiley.com/doi/10.1046/j.1365-3059.2001.00594.x/… makes no mention of sulfur compounds at all over innoculated samples. $\endgroup$
    – Fred Senese
    Commented Jan 23, 2015 at 16:58
  • $\begingroup$ @FredSenese wrote, "makes no mention of sulfur compounds at all over innoculated samples"?? Benzothiazole was the largest signal seen in the headspace of the tubers inoculated with pathogens, it was not present in the sterile water inoculated tuber headspace. $\endgroup$
    – ron
    Commented Jan 23, 2015 at 17:17
  • $\begingroup$ Oh, oops! I meant it makes no mention of your sulfur compound. $\endgroup$
    – Fred Senese
    Commented Jan 23, 2015 at 17:19

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