Polymerised oil
Heated oil cross-links into a hard varnish. The same reaction gives a cast iron pan its seasoning and an air fryer its brown film.
In detail
An oil heated in air does not merely evaporate or burn; it reacts with oxygen and cross-links into a solid, tenacious polymer film. Understanding that as one process explains two things that look opposite. On a cast iron pan the film is the point — seasoning is deliberately polymerised oil bonded to the metal, providing release and corrosion protection, and it is rebuilt when it wears. On an oven wall, an air fryer basket, an extractor filter or a grill pan the same film is the problem, and it is why detergent fails: a surfactant emulsifies oil, and this is no longer oil. What removes it is either a strong alkali, which converts fat into soap chemically, or pyrolysis, which is what an oven's self-clean cycle does by heating the deposit until it turns to ash. That is also why the deposit gets harder to remove the longer it is left and the more heat cycles it sees — each one advances the polymerisation. The sticky brown film on a kitchen surface near a hob is the same chemistry at low temperature: airborne cooking aerosol, settling and slowly oxidising.
Why
- Oven cleaner is explained by Polymerised oil
- Pyrolytic (self-clean) cycle is explained by Polymerised oil
- Soleplate is explained by Polymerised oil
- Hob surface is explained by Polymerised oil
- Lipase is explained by Polymerised oil
- Air fryer is explained by Polymerised oil
- Air fryer heating element is explained by Polymerised oil
Sources for this page
Sources
How to Clean seasoned cast iron
Lodge Cast Iron (Lodge Manufacturing Company) · Manufacturer documentation
Relied on for: That seasoning is oil bonded to the iron by heat, that it provides the cooking surface, and that it is maintained by drying and re-oiling. (states this directly)
Use and Care & Installation Guide: Self-Cleaning Electric Range
GE Appliances · Manufacturer documentation
Relied on for: That the self-clean cycle removes soil at high temperature leaving white ash to be wiped away. (states this directly)