Stainless Steel Ball Valves are used in commercial

Stainless Steel Ball Valves are used in commercial and industrial applications for a full range of liquids and gases. It features a bottom-loaded blowout-proof stem, PTFE seats and stem thrust bearing, a stainless steel ball and stainless steel body with mounting pads for actuation.
Stainless steel ball valves are almost a necessity in homebrewing.  These are most commonly used on your kettle, allowing you to control the flow of your liquids during transfers.  Using stainless steel is recommended, as these will come in direct contact with your wort, and using anything other than stainless could leave a metalic taste in your beer.  Stainless steel is also easier to keep clean, and will last longer.