system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5, why is that that milk stays good in the fridge until the expired date, but if I make a recipe like soup and it has milk in it, the soup supposely go bad faster because of this ingredient and doesn’t even last a week in the fridge?

Update: thank you so much for taking some of your time to explain me this!!
gpt
Milk goes bad because of bacteria in it, that ferment the milk. The milk that you buy from the supermarket is pasteurised   (heated to 60 deg for a long time) to kill most of the naturally occuring bacteria. Some bacteria still remain but they grow very slowly due to the cold temperature of the fridge. Together, the pasteurization and refrigeration, make the milk last longer.

When you put milk in something else, that something else (like vegetables in soup) has not been pasteurised / sterilized and has bacteria. These bacteria spoil the milk.