Eeew

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Moe C on 7 Oct 2025 at 15:24

I made an onion, parmesan loaf today. It sounded good, smelt good, and tasted like old socks. I'll try toasting it, but don't hold out much hope. 

only for sulphur smell onions old socks
 

 

 

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The "sulphur smell" that can be found in onions and old socks is caused by volatile organosulfur compounds, which contain sulfur

. While the specific chemical pathways are different, the unpleasant smell in both cases is a product of biological breakdown and chemical reactions. 

Sulfur compounds in onions

Onions belong to the Allium genus, and the strong smell is a chemical defense mechanism. 

  • When an onion is cut or damaged, its cells are broken, and an enzyme called alliinase mixes with sulfur compounds, like isoalliin, that were previously kept separate.
  • This reaction creates new, unstable, and volatile sulfur compounds called thiosulfinates and sulfenic acids.
  • The reaction happens immediately upon cutting, which is why the characteristic pungent smell of onions is released.
  • When cooked, these compounds change, which is why onions become sweeter and less pungent. 

Sulfur compounds in old socks

Socks and feet can develop a sulfurous smell from a combination of bacteria and sweat. 

  • Sweat provides a warm, moist, and nutrient-rich environment for certain bacteria to thrive.
  • Bacteria on the skin of the feet, such as Kytococcus sedentarius, break down dead skin cells and oils.
  • In the process, these bacteria release waste products that include volatile sulfur compounds, which produce the "rotten egg" smell.
  • A medical condition called pitted keratolysis, which can cause severe foot odor, is also linked to an overgrowth of these sulfur-producing bacteria. 

Common chemical link

While onions and socks don't produce the exact same suite of chemicals, the shared smell comes down to volatile organosulfur compounds. This class of molecules is notorious for its low odor threshold and potent aroma, and includes the culprits responsible for skunk spray, flatulence, and the smell of natural gas added for safety. 

Our strong evolutionary aversion to these smells comes from a need to avoid rotting food and other harmful substances. The smell serves as a warning, though humans have learned to appreciate some sulfur compounds in our cooking. 

Although the article blames the onions, I'm blaming the cheese. A toasted slice today was much better. 🤪

By old socks, I meant "cheesy", and although parmesan isn't a strong cheese, there are cheeses that could pass for "old socks" (I've heard). The outcome might have been different if I'd used real parmesan instead of the shaker can stuff, but I wanted it dry.

P.S. You know, some people can't eat coriander/cilantro because it tastes like soap. I don't know if I have that gene or not, but coriander tastes like rotten eggs to me. 

We call Romano cheese “ baby throw up” cheese 😳. It’s definitely smelly. Toasted sounds yummy. c

The pregrated is full of preservatives and cellulose . Ugh. Could be it. I’d just use a good grated cheese.

Hopefully Ian chimes in he’s the “ cheese mon “ with bread dough combinations that are cheesy / oniony and are always winners. 

Parmesan, I believe, has butyric acid in it. Can be associated with some not nice flavours. As a cheese to compliment other flavours and in small amounts it works well. But in large amounts and with onion I can imagine it might not work very well.

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Moe C on 8 Oct 2025 at 16:40

Thanks for further explanation, Abe. I'll try another cheese next time.

But some more than others. As a general rule the more pungent and aged the higher the concentration. 

Why not go for a sweeter variety onion, chopped up and caramelised, with a light(er) less pungent cheese? 

Think that will make a good combo. 

One of my favorite chemistry sites is Andy Brunning's Compound Interest. He has some posts (with graphics) that might be of interest:

The eye-watering chemistry of an onion

The Chemistry of Body Odours

The Chemistry of Camembert

The last one isn't parmesan-specific, but some of the compounds are the same. Here is a more in-depth study, if you're interested:

Identification of Aroma Compounds in Parmigiano-Reggiano Cheese by Gas Chromatography/Olfactometry

The other aspect of chemicals is how surprised you would be to find that a lot of odd and smelly compounds that, in small amounts, are responsible for the odor and flavor of foods. Take a look at Table 1 and especially Tables 2–4 in the Parmigiano-Reggiano article.

So too what goes into perfume. Look up "ambergris". To spare everyone I won't go into detail what it is and what it smells like but it is used in perfumes for its musky odor. 

If you are walking along the beach and happen to find this ambergris then you'll strike it rich. Perfume companies will pay a fortune for it. It is rare to come across it but I believe it has happened.  

Yes, lots of things in cooking when used in the correct quantities are just compliment other flavours. Salt for intance. And then there are things like Asafoetida which is very pungent but when paired with the correct ingredients it enhances. Cooking/Baking is a science. 

If you think ambergris is an unusual source for perfumery, then you really don't want to know about castoreum!

Haha being married to a Chemistry professor has its pluses. He’s always telling me the why of odors and flavors. 

It’s amazing how food scents come out of the bodies pores. I once ate a very heavily garlic forward dish in Atlanta. For days afterwards the “ fragrance “ came out so that everyone in my house could smell me! Very off putting to say the least. 

I have found that using Lava soap on armpits removes all traces of old deodorant and buildup of bacteria which causes the BO . It contains a small amount of pumice which is all that’s needed. A cheap and very easy healthy treatment far better than the deodorants filled with who knows what.