What is the rule for capitalization when the normally capitalized word describes a noun.
For instance is it Swiss cheese or swiss cheese?
What about the sentence “I had a fifth of bourbon then added scotch also.”
Would scotch be capitalized?
There is no one covering capitalization rule that applies in all situations. “Swiss cheese” is capitalized, while “scotch” is not. “Bavarian cream” is capitalized while “french fries” is not.
EDIT: Consider, however, that the use you offer for “scotch” is not adjectivial, as “Swiss” is in “Swiss cheese”.
I would capitalize anything used as an adjective (Swiss cheese, French fries, Italian vinaigrette), but not as a noun or verb (china, to japan furniture).
“Scotch” is an adjective that can describe only whiskey, not people, who are Scottish; it is therefore lowercased even when used as an adjective (scotch whiskey).
I would capitalize when the adjective actually is used to descibe the national origin of a more general category of food, but leave it uncapitalized when it is part of the name of the product. So “french fries” and “scotch” (mmm… 
) because with french fries, there is no other type, and they aren’t from France, and with scotch, like matt-mcl says, it is not the current name of any country or ethnicity. I would say “swiss cheese,” too, since it is not actually made or consumed in Switzerland for the most part, but you could debate me on that one. However, I think “Italian vinaigrette” and “Canadian bacon” are proper because there are other types of bacon and vinaigrettes.
ETA (or it would be if Guests could edit): You picked a funny example in the OP because bourbon and scotch actually both relate to places.
Either is understandable and both are in common usage, so whichever you like.