Can you explain the expression a drop of scotch?

The expression "a drop of scotch" refers to a small amount of Scotch whisky, typically consumed neat (without ice or water). It is often used in a figurative sense to indicate a minimal or insufficient quantity, as in the phrase "he doesn't know a drop of scotch about the subject." In this context, "a drop" is used to emphasize the speaker's perception of the person's lack of knowledge or expertise in a particular field. However, "a drop of scotch" can also refer literally to a small amount of whiskey poured into a glass for actual consumption.