There are certain types of cheese that have an unpleasant odour – e.g. Limburger or some Camemberts.
No matter in how many layers of plastic bags I enclose the cheese before storing it in the fridge, the smell will always become pungent. Sometimes it’s so strong that the stench is capable even of escaping the fridge.
**How is it possible that the odour is able to escape both packaging and fridge?**
Side question – is human nose particularly sensitive to these smells?
In: Chemistry
Tldr: two reasons: defects in the wrapping, and smelly molecules actually making it through the plastic itself.
The wrapping is not as perfect as you think. It’s leaky in places.
Small modules are able to travel through plastic food wrapping istelf, though. This isn’t just because of the defects in the welded seams of the wrapping but because of two other phenomena that allow the volatile smell molecules to go through the actual plastic:
1. Some molecules are ‘soluble’ in the plastic itself. They have an affinity for it and are attracted to it and if they are small enough will get into the wrapping and exist between the molecules of the plastic.
2. A difference in concentration of the smelly molecule: much much more exist on the cheese side than on the outside. This creates a pressure on the smelly molecules to continue diffusing through the plastic and out the other side; those that have dissolved into the fabric of the plastic, are pushed along by other molecules also wanting to dissolve into the wrapping.
Second part of the question has to do with how inherently smelly something is. It’s called olfactory yield. Some molecules are actually much smellier than others. Some organic acids and sulphur containing compound found in food are just very smelly.
The smelliest molecule I know of is one found in grapefruit, called grapefruit mercaptan. I once calculated that if you put a single miniscule drop into an Olympic swimming pool of water, you would be able to smell grapefruit.
Edit. I wasn’t going to mention any physical chemistry laws in this ELI5 but I’ve just seen your username.
The solubility of the smelly molecules is the plastic is governed by…. HENRY’S law.
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