The spices in some of the hot foods that we usually eat are oily, and I think your school science teacher must have taught you that oil and water don’t mix. In this case, the water just rolls over the oily spices.
So what can you do to calm your sour tongue? Just go and eat a piece of bread. The bread will absorb the oily spices. Another solution is to drink milk. Milk contains a substance called “casein” which will bind to the spices and carry them away. and on the other hand, alcohol also dissolves oily spices.