There’s something about diner coffee that is comforting, despite the fact that it's not that good. This is due to factors like bean type and methods of roasting and brewing.

How long coffee sits is another factor. Diners serve coffee hot, and depending on when you order it, it may have been sitting on a warmer for a long time, which changes its flavor.

Depending on when you order your coffee, it may be poured from a brand-new pot with a pleasant, fresh taste, or a pot that's been sitting, resulting in that slightly sour flavor.