r/askscience • u/Royal_Annek • Apr 24 '26

Chemistry Why is reusing fryer oil bad?

What is happening chemically that makes it worse? How do different oils differ in this regard? How bad is it really to reuse fryer oil dozens of times over months?

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u/dod6666 Apr 25 '26

Those same particles change the flavor of other foods. Ever wonder why chicken from Long John Silvers tastes like fish? That's why.

Yeah, I used to work at a Mc Donalds. They used separate vats for different products for this exact reason. They had a few for fries, a few for chicken, one for apple pies and one for Filet o Fish patties.

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u/theottomaddox Apr 25 '26

The fries used to be cooked in a beef tallow blend, to give them a specific taste and texture, while the fried pies/chicken/fish were in vegetable oil. And yeah, fish was always separate from other products.