Expiration Date on Milk
What does the expiration date on milk cartons mean?
I have different experiences with the date:
- There is still about a week before the expiration date but the milk has gone bad
- It is 1-2 days after the expiration date but the milk doesn't smell or taste bad
In both case, the milk was kept in the fridge.
There is a lot of variability in how fast milk will go bad.
- How long the milk has been opened
- Pasteurized vs ultra-pasteurized
- Temperature the milk is kept at
- Thermal cycling: how long and how often is it kept above 40º
- Where in the fridge it is kept. The door will have more thermal cycling than a shelf, higher shelves tend to be warmer than lower ones.
All of these influence how long milk stays good. The big date on the top is used by grocers to determine when it can't be sold. If you look closer there will be text to the effect of, "Use within 7 days after opening". This isn't a guarantee. Leaving the carton out while you cook will allow it to go bad faster, as will keeping it in the door. Also if your fridge is too warm for some reason, things will spoil faster.
I'm of the opinion that how long it's been opened has more impact than the date itself.