So I just heard about putting a carrot in the deep fryer so as to pick up the burnt junk and keep the oil clean for longer. I tried it. It works! Now I'm wondering how it works, and what other veggies or whatnot can be substituted in place of the carrot?
As to the science behind why this works, I can only guess.
However, as to other things you can try for this trick, I managed to find some references from old cookbooks about using slices of potato for clarifying their deep-fryer oil. Other suggestions were a slice of bread or lemon peel. Weird — but interesting.
When you have finished frying, clarify the oil by frying a piece of bread, a strip of lemon peel, or a slice of potato in it.
I am wondering if the mechanic behind this is the same as that used to clarify wine in the winemaking process. Some wines have a predilection to get cloudy with colloidal material, or just tiny particulates held in suspension. If a wine does not clarify on its own through gravity/sedimentatin, you can add ingredients to it that will by one mechanic or another join with the particals, and allow them to fall out of solution. Some of these reactions are ionic, some are absorbative, some just are gunky and sticky to the particles.
Examples are a clay from wyoming, I can't remember the exact name. egg yolk issinglass (it comes from fish guts)
I wonder if the potato and carrot have something that binds to the particles in the oil in a similar fashion.
I'm not sure where you got the idea, but it most likely does not work at all - the carrot does not clean the oil, the sugars in it are just getting caramelized by the heat, so the carrot gets darker and darker because it gets burned.
I suspect it can even be the reason why the oil was getting darker towards the end. If this trick worked, everyone would be using it for decades by now (especially fast food chains).
There are other techniques which seem to work, such as the gelatin technique.