When I made my very first version (not on this page though) I mixed various metals, and hence forgot all about metal-chemistry. So there was brass, bronze, stainless steel, metal-clamp and then plastic all neatly joined into a stainless steel pot. It was a metallic taste disaster as less tolerant metals down the metal-chain released there ions.
Hence, not to go to much into chemistry of metals it important to hold only one type of metal (preferably stainless steel) combined with heat-tolerant plastic. Generally the white plastic fermenters can be fund tolerant till 110´C and the silicone tubing’s are rated at 100´C.
If you wish to learn a bit on toxicology of home brewing in general and in regards of those materials we might use, please see below links:
From “Basic Brewing Radio”:
November 14, 2013 – Homebrew Toxicology
Paul, a homebrewer and toxicologist, answers your concerns about materials and chemicals we use in our favorite hobby.
December 12, 2013 – Homebrew Toxicology Pt. 2
Toxicologist Paul joins us again to follow up on your questions about possible toxic materials in homebrew.
February 27, 2014 – Homebrew Toxicology Pt. 3
Toxicologist Paul joins us for the third part of our exploration of whether our ingredients, processes, or equipment are hazardous.