I can smell a urine like odour from some coffees. I don't seem to be alone in this as there are multiple reports on the internet of people having the same experience.

I have read from a few posts that results of the Maillard reaction create ketoamines that could be causing it.

What's the science behind this?


  • $\begingroup$ Actually I have similar experiences. Often, after drinking caffeinated beverages or coffee-flavoured pastries, I observe greenish tinge of colour in my urine and a familiar coffee-like smell. This question may also fit well on Biology StackExchange. $\endgroup$ Dec 21, 2018 at 14:43
  • 5
    $\begingroup$ @TanYongBoon well, coffee-smelling urine or urine-smelling coffee is not exactly the same thing ... $\endgroup$
    – mannaia
    Dec 21, 2018 at 15:00
  • 2
    $\begingroup$ @mannaia That is true. Actually, I have never drunk urine-smelling coffee before. It would be weird to think that coffee could smell like urine. Unless... One drinks a lot of coffee, such that one's urine smells like coffee. Then, one can assert that "my coffee smells like my urine"... And that would be correct :) $\endgroup$ Dec 21, 2018 at 15:05
  • $\begingroup$ There are surely plenty of molecules in coffee and surely lots of them contain nitrogen. Ammonia and amines are most likely formed or released upon roasting. Coffee is good because it comes in a huge number of reach and complicated aroma. As stated in other places here urine doesn't smells particularly unless for specific states of the body or dietary reason. $\endgroup$
    – Alchimista
    Dec 22, 2018 at 16:11

1 Answer 1


This answer is purely speculative in nature fueled by high school science and a research paper

From medicalnewstoday

Urine does not usually have a strong odor to. However, occasionally, it will have a pungent smell of ammonia.

Googling coffee + ammonia led me to this little article Filter coffee nanoparticles to turn ammonia sensors.

The article says that the researchers at IISC Bangalore were using coffee powder for detecting ammonia because coffee powder contains carbon and nitrogen in abundance and they've used that to make carbon nanotubes whatnot.

Then I hit gold when I found the research paper itself
- Understanding the ammonia sensing behavior of filter coffee powder derived N-doped carbon nanoparticles using the Freundlich-like isotherm.

The detecting technology is based upon adsorption which is a surface phenomenon basically the adsorbate(ammonia) gets concentrated only at the surface of the adsorbant(coffee powder).

Now, there are two types of adsorbtion.

  1. Chemisorption
  2. Physisorption

Now comes the speculation I'm assuming that the process over here is physisorption because physisorption is inversely proportional to temperature.

How it works?.

Filter coffee is essentially a powder this provides a large surface area for adsorbtion.

Intially when the coffee in your kitchen at room temperature some amount of ammonia gets adsorbed on it. Now, when you make the coffee it is exposed to high temperatures and as you can recall I just discussed that in physisorption the amount of gas adsorped on the surface is inversely proportional to temperature so the hot coffee can hold less amounts of ammonia on its surface as compared to the room temperature coffee.

So that's how ammonia is released on making coffee. Presumably.

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    $\begingroup$ Intriguing, but where does the ammonia come from in the first place? $\endgroup$
    – orthocresol
    Dec 21, 2018 at 16:46
  • $\begingroup$ The atmosphere? $\endgroup$ Dec 21, 2018 at 16:47
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    $\begingroup$ If urine is stinking ammonia that's a sign someone is close to death. If in your atmosphere there's so much ammonia that coffee is stinking then better get out of there. $\endgroup$
    – Mithoron
    Dec 22, 2018 at 0:59
  • $\begingroup$ Interesting speculation though $\endgroup$ Dec 22, 2018 at 13:20

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