First, some background. I've been using a setup very similar to this -
Almost identical actually. 120V 1500W high-density element in a 7.5 gallon aluminum pot.
I've successfully used this setup on 2 extract and 5 all-grain brews without incident. Then last night happened....
Shortly after I put my wort chiller (immersion) into the pot towards the end of the boil I noticed a slight burned smell. I didn't think much of it (I brew in my kitchen on the stovetop), but it continued to get worse, then I noticed intense steam (possibly smoke) coming from the kettle. Next thing I know the GFCI trips.
I was basically done with the boil so I went ahead and chilled. The wort definitely smelled scorched/burned and had a slight smoke taste (guess I will have a Smoked Saison now...), but the really bizarre part was how the element looked.
Once I scraped off the black burned material the element looked like it had copper on it, almost like it had electroplated itself. The element also clearly looked like it overheated significantly (used to be shiny silver, now looked like metal that had gotten extremely hot).
Anyone have any experience similar to this? I have several possible theories:
1) I was using a grain bill high in Rye and had a hell of time getting this thing to sparge. Ended up with a very cloudy (presumably protein-rich) wort. Did protein accumulate on the element eventually causing it to overheat?
2) Some sort of bizarre reaction with the wort chiller