"When not to capitalize. Personal, national, or geographical names, and words derived from such names, are often lowercased when used with a nonliteral meaning. For example, the cheese known as "gruyère" takes its name from a district in Switzerland but is not necessarily from there; "swiss cheese" (lowercase s) is a cheese that resembles Swiss emmentaler (which derives its name from the Emme River valley). Although some of the terms in this paragraph and the examples that follow are capitalized in Webster's, Chicago perfers to lowercase them in their nonliteral use."
Chicago Manual of Style 16th Edition