Which one goes sour fastest cows milk or soy milk and why

Is this HOMEWORK?

I would say Soy milk. It taste like crap any time.

Soy milk has no why. Cow milk does. That answers the Q.

When it come to Soy milk, I could never answer why.

Dairy milk usually goes first because soy is a plant product which has a little bit longer shelf life than a product made by an animal... The enzymes in cow milk are still trying to make cream and butter fat which is what you see when you let milk go bad and turn sour... you just can't drink it because it has already gone through pasturization and homoginization process... either way they are both nasty when old...