Dear WO'N: I have often heard complaint about food kept in refrigerator too long
hving an :off flavor".
My dictionary as sixth meaning of "off" as an adjective gives:
not up to what is usual, normal, standard, etc. !an off day"

Just as wine was discovered by accident, cheese etc. was undoubtedly found by accident.
Milk would have been so valuable, it would not have been thrown away just because it was
"rotten".