Smell molecules escaping
Why Does a Fridge Smell of Everything at Once?
Every food quietly releases molecules, and a sealed cold box gives them nowhere to go.
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Step 1 of 5
Smells are molecules that have gone airborne.
Any food constantly loses a few of its lightest molecules to the air. Those are what your nose catches — smell is always physical.
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Step 2 of 5
A sealed fridge lets them build up.
In a room those molecules disperse into thousands of litres of air. In a fridge they stay in a small sealed volume and concentrate.
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Step 3 of 5
Fat absorbs them and keeps them.
Many smell molecules dissolve in fat far better than in water. Butter and milk soak up whatever is drifting around and hold on to it.
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Step 4 of 5
Cold slows the process but does not stop it.
Chilling reduces how many molecules escape each hour, which is why a fridge smells less than a warm cupboard would. Days are long enough anyway.
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Step 5 of 5
Covering beats deodorising.
Bicarbonate absorbs some smells, but a closed container stops them leaving in the first place, which works far better.
Airtight really does mean airtight — most plastic wrap over a bowl lets plenty of smell molecules through.
The short version
Foods release smell molecules that build up in a sealed fridge, and fatty foods soak them up and keep them.
Try it yourself
Put a peeled onion beside butter in the fridge overnight in an open dish. Taste the butter in the morning.
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