The simple answer is that expired milk is discarded and not used for anything, such as cheese, sour cream, or yogurt. As for the rumor that chocolate milk is made from sour milk, it's not true. No amount of added boiling and flavor could eliminate the sour taste of spoiled milk. Shelf-life milk is pasteurized at ultra-high temperatures, which will be labeled on the package as “UHT milk” or “ultra-pasteurized milk”.
Unopened and stable milk on the market can generally last between two and four weeks after the expiration date if stored in a cool, dry space, Healthline reports. In addition, non-perishable milk is packaged in special plants that use completely enclosed equipment to ensure that everything is kept very clean.