> There’s a secondary argument about oxidation — seed oils go rancid at high heat, producing potentially harmful compounds. This idea is chemically real and worth being thoughtful about (don’t reuse frying oil repeatedly). But the evidence that oxidation at home-cooking levels causes measurable harm in humans isn’t there. Even if oxidation at home-cooking levels doesn't cause harm, which I suspect that it does though…
I work in an area that involves, among many other things, analysis of cooking oil in factories. It might be hard to pin down the terminology of "reused" frying oil, because many of the frying processes are continuous. The raw material goes through a vat of hot oil on a conveyer and comes out the other end dripping with oil The quality of the oil is continuously monitored, and new oil goes in while old oil goes out in…
Vodka is made almost exclusively in industrial-scale continuous fractionating columns. The concept of it being “distilled N times” is farcical. (But technically defensible because you can map the output of the fractionating column to any arbitrary N via equivalence relationships.)