Step 1: First Way
Step 2: Second Way
Step 3: Third Way
You will need to add salt to the 2 drinks and see which one reacts to it.Pepsi will let off gas when salt is added.So with this,you will know which is which..
Step 4: Forth Way
Nothing gets better than this.When you see the pepsi just blows up when you add a mentos to it.This is so far the best way to distinguish pepsi and coffee.Just remember to clean the place after that or ants will be marching!