Not sure if this is the correct category for this but I was reading the book "Brew Ware" by Stevens, and Mosher and they mentioned copper as being a yeast nutrient and suggested cutting a small peice of copper tubing and throwing it into your boil kettle with the wort. I guess this makes sense considering most traditional breweries have/had copper kettles. Just wondering if anyone actually does this on a regular basis. Thought I'd give it a try next time I come across a small piece of copper.