Butyric acid.. stinks?

Its name comes from the Latin word butyrum, meaning butter, because it was first extracted from rancid butter by the French chemist Michel Eugène Chevreul. It’s a fatty acid, which means it’s one of the building blocks of fats. The fat molecule made from butyric acid makes up 3-4% of butter.

It’s generally found in dairy products, and is a product of anaerobic fermentation. Hence the links to butter and parmesan cheese. And.. as well known, butyric acid is what gives vomit that distinctive, smell-it-a-mile-off, odor.

And this is why we’re so good at detecting it. Humans can pick this stuff up at 10 parts per million. Evolution has trained us to detect and avoid this stuff because it’s very probably a sign of disease and potential infection (gone-off food, vomit, faeces etc).

Funnily enough though, it does have its uses. There are molecules called esters which can be made from butyric acid which actually smell rather nice. In particular there’s one that has a lovely apple-pineapple smell, and another that smells of apricots and pears. As a result, these much nicer-smelling substances are used as food and perfume additives.

Butyric acid also helps to prevent salmonella bacteria from taking hold in animal husbandry, and as result it’s used as a feed additive. And perhaps not surprisingly it’s been used, along with a cocktail of other stinky stuff, in stink bombs.

So even the stinkiest of molecules has it’s uses, and maybe it’s not so bad after all. Makes you wonder how anyone ever developed a taste for parmesan cheese though, doesn’t it?