I've just bought some wheat, rice and almond milk in Prague, CZ. The thing is that this rule applies only if it's not known that it is a metaphor - e.g. there is a "rum drink" that is not a rum and it used to be called "tuzemsky rum" (local rum), now it's "tuzemak" (abbreviation of the first word); similar situations was with different kinds of fruit jams. At the same time, almond milk... well, everyone knows almond tree is not a cow.
