system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why does milk become spoiled when left in the heat but not when heated?
gpt
Milk is spoiled by bacteria. Most bacteria grows fastest in a warm environment. Leaving milk to warm up over a long period of time gives the bacteria the warmth it needs, and plenty of time to multiply. When you heat milk quickly the bacteria doesn't have enough time to grow to substantial numbers and spoil the milk.