Finding tiny white flakes in your milk can be alarming, especially when the expiration date hasn’t passed. But an unopened carton can sometimes develop harmless particles for several reasons. In colder temperatures, natural milk fat can separate and form small white pieces, particularly in non-homogenized milk. Tiny bits of dried milk residue from the carton’s seal can also break loose when you pour.

Temperature changes can play a role, too. If milk becomes extremely cold during transportation or storage—especially if it gets close to freezing—the fat and other milk components may separate and create visible specks. These changes don’t automatically mean the milk has spoiled.

However, the expiration date isn’t a guarantee that milk is safe. Improper refrigeration or exposure to warmer temperatures can cause milk to spoil before the printed date. Check the smell and texture: fresh milk should have a mild, slightly sweet smell and a smooth consistency. A sour odor, thick texture, clumps or obvious curdling are signs that it should be discarded.

When you notice flakes, pour a small amount into a clean glass and examine it carefully. If the milk smells normal, looks otherwise smooth and the flakes disappear after gentle mixing, separation may be the explanation. If anything seems unusual—particularly a sour smell or significant curdling—it’s better not to take chances.

The expiration date is only one clue. How the milk was stored and what you see, smell and feel are also important when deciding whether it belongs in your fridge or the trash.