why does mixing milk of the different temperature make it go bad faster?

Question

I’ve seen this rule for pumped milk: never add a new portion of warm milk to the portion pumped earlier and kept in the fridge, until the new milk cools down to the same temperature. Adding warm to warm is also fine. Why?

In: 2

Answer 1

The temperate GREATLY affects the rate at which chemical reactions happen, including the reactions that keep bacteria alive and allow them to soil foods. When adding warm to cold, you are raising the temperature of the stuff rhat was cold, which may include potential pathogens/organisms that will spoil the milk. By allowing the new milk to cool you remove the risk of activating anything that was already present, but dormant because of the cold.