I'm making a soup and the last step calls for adding ermilk...?

its a cold cuber lime soup. i've tasted what i have so far and its VERY tart. the last step before chilling it, is to cool it (which its doing right now) and then add ermilk. my question is, the soup is already PLENTY tart for my taste, so, won't the ermilk, being essentially tart milk, make it even MORE tart? or does ermilk do some magical thing i'm unaware of where it lessens the tartness of foods? if it does what i think, and makes the soup even more tart, then i will just substitute the ermilk with extra coconut milk from the earlier steps instead...that should work too, right?