In Chapter 23 of To Kill a Mockingbird, when Aunt Alexandra forbids Scout to bring Walter Cunningham to the house to play with her, she stresses that the Finches are different from the Cunninghams because Walter is "trash." Angered by her aunt's cruel remark, Scout is led in her "fury" to her bedroom. There Jem attempts to explain that a family's background makes all the difference in their society. For, while Atticus pats his foot when men play the fiddle on the radio, just as country folk do, and "he loves pot liquor better'n any man"--meaning that he eats what the Southern poor people do: the liquid left after boiling turnip or collard greens, which are often ingested with cornbread--Atticus is yet not on the social level of the Cunninghams. He is from a well-bred family that has traditionally been better educated and less in-bred (note the reference to "double cousins") than the sharecropper families of the area. This socio-economic difference is something that the innocent Scout does not understand.
The "pot liquor" Jem refers to is not alcoholic. It is the liquid left in a pot - later used for gravy or broth - after meat or vegetables have been cooked. Jem makes his observation as he and Scout try to make sense of the social structure in Maycomb. Earlier, acting magnanimously, Scout had floated the idea of inviting Walter Cunningham to lunch, an idea which Aunt Alexandra torpedoed by remarking that Finches were not the social equals of people like the Cunninghams. Aunt Alexandra's prohibition reduces Scout to tears and Jem takes her upstairs. There, after she calms down, Jem sketches his version of the town's social structure: "There's four kinds of folks in the world. There's the ordinary kind like us and the neighbors, there's the kind like the Cunninghams out in the woods, the kind like the Ewells down at the dump, and the Negroes." And between them, he remarks, is an ancient distrust and antipathy. Atticus may love to drink the broth from a pot, or tap his foot at Old Time fiddle music, but these are superficial resemblances to a class of people about which the Finches had nothing in common. Bewildered by the yawning, but incomprehensible class divisions in his own town, Jem observes at the close of the chapter that he now understands why Boo Radley "stayed shut up in the house all this time . . . it's because he wants to stay inside."