How can you tell when breast milk is too old after sitting out all day cooled?

Follow Guidelines: Un-used breast milk can be stored at room temp (66-72 deg. F) for up to 10 hrs; in refrigerator (32-39 F) for up to 8 days; in freezer for up to 4 months. Following a feeding, discard any left-over breast milk after 2 hours due to risk of bacterial contamination. More info can be found at: http://www.llli.org/docs/0_babupdate/07babupdatemilkstorage.pdf